Plant Biology / BIOL 3306

1.1. Syllabus and logistics

1.2. Why Plants?

• Why Plants?
  

  Plants aren’t the most diverse group

  • Global diversity of eukaryotes (described / estimated)
    

    Plants

    300,000 / 400,000

    Vertebrates

    65,000 / 80,000

    Invertebrates

    1.6 million / 7 million ?

    Fungi

    50,000 / 70,000

  • But they are the most abundant
    

    Plants comprise ≈ 90% of the terrestrial biomass on the planet!

  • Note   B_note
    
    • Estimates based on ?
• The world runs on plant energy
  
  • Plants are the primary producers and food source for much of the planet
  • all wildfire burns plant material
  • our industrial energy economy runs on fossil plant material

1.3. Plant form

• Wouldn’t it be great to be able to photosynthesize?
  
• Animals that photosynthesize? Elysia viridis
  

  

  • Notes   B_note
    

    This sea slug can retain chloroplasts of the algae it eats. There is some debate on how useful but most recent evidence suggests that the slug can obtain carbon from this source. There is also evidence of horizontal gene transfer.

    Refs:

    http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120874

• Key aspects of plant form
  
  • Sessile
    

    Plants stay in one place, extend their roots and shoots to harvest diffuse resources, and make their own food through photosynthesis

  • Modular
    

    The structure of a plant’s body is dynamic, because most plants exhibit indeterminate growth, in which they grow throughout their lives

• A herbaceous Angiosperm
  

  Phylogenetically: This is a land plant, vascular plant, seed plant, flowering plant.

  

• Many solutions to every problem
  

  

  • Notes   B_note
    

    Even within a single community there are annuals and perennial, woody and herbaceous plants. Some will have very thick leaves and some very thin. Some are tall and some short.

• Example: dealing with drought
  

  

• Example: dealing with drought
  

  

• Example: dealing with drought
  

  

• Example: dealing with drought
  

  

1.4. A history of plants

• Oxygen in the atmosphere
  

  

• Origins of photosynthesis
  
  • First autotrophs: at least 3.4 billion years ago
  • Photosynthesis in its current form (O₂ producing), evolved ≈ 2.7 billion years ago in cyanobacteria.
• What are the plants?
  

  

• Overview phylogeny of the plants
  

  

• Green plants and specifically, the land plants are the focus of this course
  

  

2.1. Cell overview

• The plant cell
  

  

• Prokaryotic vs eukaryotic cells
  

  	Prokaryotes	Eukaryotes
  Cell length
  Nuclear envelope
  DNA
  Organelles
  Cytoskeleton

• Recent find: Acetabularia jalakanyakae
  

  

• The plant cell
  

  

  • Exercise   B_note
    

    Review Table 3-2 in text and mark those items that differ from animal cells.

2.2. Internal components

• Endomembrane system
  
  • Endoplasmic reticulum
    

    Lipid synthesis, calcium regulation, other functions

  • Golgi apparatus
    

    Membrane system involved in synthesis and secretion of polysaccharides

  • Vesicles
    

    Membrane-bound, enclosed substances for transport

• Endomembrane system
  

  

• Organelles surrounded by one membrane
  
  • Vacuole
    

    Mature plant cells often have one large vacuole that is 90%+ of the cell. Why?

  • Peroxisome
    

    Important in metabolism, especially dealing with byproducts of photorespiration.

  • Lecture notes on vacuoles and peroxisomes   B_note
    
    • Mature plant cells often have one large vacuole that is 90%+ of the cell. Why?
    • Contains “cell sap” (mostly water). Pressure in this vacuole pushes against cell wall and keeps cell rigid and plant from wilting.
    • Contains mostly water, but also solutes such as Ca2+, K, Cl-, NA+, HPO42- (cell sap)
    • Can contain pigments (anthocyanins). Fall color in leaves.
    • Can store toxins and secondary metabolites used in defense (eg nicotine). Toxic to plant!
    • glyoxysomes (specialized peroxisomes) help convert stored fats to sucrose in seed germination. Plant and fungi specific!
    • peroxisomes are self-replicating but must import materials no DNA)
• Organelles surrounded by two membranes
  

  And have their own DNA

  • Plastids
    

    Chloroplasts, leucoplasts, and chromoplasts.

  • Mitochondria
    
  • Nucleus
    
  • Lecture notes on plastids   B_note
    
    • Chloroplasts are site of photosynthesis
    • Chromoplasts lack chlorophyll (can develop from chloroplasts). Synthesize carotenoids responsible for some flower and fruit colors.
    • Leucoplasts are unpigmented. Most important are starch synthesizing amyloplasts. Also plastids that store fats or proteins.
    • proplastids are the undifferentiated forms (eg in seeds).
    • plastids must reproduce by division.
    • mitochondria - similar and often congregate where energy is needed in cell (eg at membrane involved in active transport).
    • Both plastids and mitochondria have DNA that codes for some, but not all of their own polypeptides. Semi-autonomous.
    • plastids can change into one another.
• Chloroplast
  

  

• Chloroplasts
  

  The site of photosynthesis

  • Light energy converted to short term ATP and NADPH in the thylakoid stacks (grana)
  • ATP and NADPH and CO\(_2\) converted to sugar in the stroma
• Chromoplasts of a red pepper fruit
  

  

2.3. Cell wall and cytoskeleton

• Cytoskeleton
  

  Protein filament types: actin filaments and microtubules

  Active in organizing cell growth and division and cytoplasmic flow.

• Cytoplasmic streaming exmaple
  

  https://www.youtube.com/watch?v=BB5rvjZzgFU

• Primary cell wall
  

  Deposited before and during cell growth.

  

• Cell wall components
  
  • Cellulose (polysaccharide) bundles are interlocked with hemicellulose, pectins, and glycoproteins.
  • Cutin, suberin, and waxes can be part of the cell wall
• Cellulose extrusion
  

  

• Cellulose extrusion
  

  

• Secondary cell wall
  

  

• Pits and plasmodesmata
  

  

• Pits and Plasmodesmata
  

  

3.1. Modular growth

• Key aspects of plant growth
  
  • Unlike animals, plants have partially differentiated meristems throughout their body and throughout their life
  • Plants are modular
  • Plant growth is indeterminate
  • Plants are sessile but can use growth as their behavior instead of motility
  • Plants have three vegetative organs: stems, leaves, and roots
• Modular shoot growth
  

  

• Repeated modules
  

  

• Huge variation in size
  

  

• Huge variation in size
  

  

• Shoot apical meristem
  

  

• Root apical meristem
  

  

3.2. Tissue types

• Primary meristems and tissues
  

  Apical meristems produce daughter cells that partially differentiate into primary meristems.

  • Primary meristems
    
    • Protoderm: produces the epidermis
    • Ground meristem: produces ground tissue system
    • Procambium: produces the vascular tissue
• Cell differentiation
  

  

• Distribution of major tissue types
  

  

• Ground tissue system
  

  Parenchyma cells

  In leaves, contain chloroplasts. In other organs, may store starch. Totipotent

  Collenchyma cells

  Typically Long and thin, support plant body. Primary cell walls of uneven thickness.

  Sclerenchyma cells

  Fibers and sclerids. Thick secondary cell wall. Usually dead at maturity.

• Parenchyma cells: leaves
  

  

• Parenchyma cells: roots
  

  

• Transfer cells (parenchyma)
  

  

  • Lecture notes   B_note
    

    Transverse section near tip of phloem tissue in leaf in a sow thistle. Facilitates solute transfer.

• Collenchyma cells
  

  

  • Lecture notes   B_note
    

    Living at maturity. Surround leaf and petiole veins. Strings of celery are collenchyma tissue. Unevenly thickened primary cell walls. These are from rubarb petiole (part you eat).

• Scerenchyma cells: fibers
  

  

  

• Yucca fibers
  

  

• Yucca fibers
  

  

• Yucca fibers on leaf margin
  

  As well as around vascular bundles

  

  • Lecture notes   B_note
    

    See TTU MS Thesis by Anthony Eagan, 1969

    https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwicwLGK04SBAxVxk2oFHfhvC2MQFnoECAIQAQ&url=https%3A%2F%2Fttu-ir.tdl.org%2Fbitstream%2Fhandle%2F2346%2F11000%2F31295015504862.pdf%3Fsequence%3D1&usg=AOvVaw13m5TYgADXrswBd-GbB6HC&opi=89978449

• Yucca fibers: baskets and rope
  

  

• Scerenchyma cells: sclerids
  

  

4.1. Vascular tissue system

• Distribution of major tissue types
  

  

• Xylem tissue
  
  • Tracheary elements (dead at maturity):
    

    tracheids

    Long, narrow, only pits

    vessel elements

    can be wider, perforation plates + pits, stack together

  • Other xylem cells:
    

    Xylem can also contain parenchyma cells (alive), fibers, and sclerids.

• Tracheid and two vessel elements
  

  

• Vessel elements
  

  

• Formation of vessel elements
  

  

• Phloem tissue
  
  • Sieve elements (alive with protoplast):
    

    sieve elements

    General term and term for simplest type found in non seed plants

    sieve cells

    with associated albuminous cells (found in gymnosperms)

    sieve tube elements

    with associated companion cells (found in angiosperms)

  • Other cell types in phloem:
    

    parenchyma, fibers, sclerids

• Sieve tube element and companion cell
  

  

• Sieve tube element and companion cell in barley
  

  

• Sieve tube elements in squash
  

  

• Sieve tube elements in squash
  

  

4.2. Dermal tissue system

• Epidermis
  
  • Covers exterior of all plant parts
  • Hinders water loss (cuticle)
• Stomata
  

  

• Trichomes and root hairs
  

  

7.1. Root Overview

• Taproots and fibrous roots
  

  

  • Lecture notes   B_note
    

    Two plants that you can find growing wild around Lubbock in the shortgrass prairie. Liatris punctata and Aristida purpurea

    In monocots, the original primary root is short lived and the root system mostly develops from adventitious roots – roots that develop from the stem. This is the same thing as when a shrub with a drooping branch forms roots where the branch touches the ground.

    Most of the root length and area is in the fine roots / feeder roots.

    Some roots have been measured very deep (53 m in mesquite in arizona in a mine), 68 meeters for a Kalahari shrub.

• Root external overview
  

  

  • Lecture notes   B_note
    
    • Root and shoot are balanced and balance depends on environment
    • Lateral roots do not form at nodes
• Review: Distribution of major tissue types
  

  

• Root growth
  

  

  • Lecture notes   B_note
    
    • regions: cell division, cell elongation, maturation
    • Root hairs develop behind region of elongation, older parts of roots lose hairs (die)
    • phloem develops early – growing tip needs carbon source, xyelm mautres behind this
    • Endodermis and casparian strip develops as maturation occurs
• Root cap and apical meristem
  

  

• Root cap - sensing gravity
  

  

• Growth without the root cap
  

  figs/rootnocap.mov

  • Lecture notes   B_note
    
    • central portion of root cap senses gravitropism
• Root cap and border cells
  

  

• Root hairs are single cells
  

  

  • Lecture notes   B_note
    
    • example study of a rye grass plant estimated that root hair total length was over 10,000 km. and 401 m² length.
• Root hairs
  
  • text   B_ignoreheading BMCOL
    

    Can get between soil particles to extract water and minerals.

  • figure   B_ignoreheading BMCOL
    

    

7.2. Internal morphology

• Root cross section: eudicot
  

  Epidermis, (exodermis), cortex, endodermis, vascular cylinder

  

  • Lecture notes   B_note
    
    • Phloem to outside, xylem inside as in shoots
    • Non vascular cells inside the vascular cylinder are the pericycle (parenchyma)
    • Lateral roots arise inside the pericylcle! and burst through.
• Root cross section: monocot
  

  

• Symplast and apoplast
  
  • Symplast
    

    Everything within the cell membrane

  • Apoplast
    

    Almost everything outside the cell membrane (xylem, water space in cell walls, water-filled spaces between cells).

• Casparian strip
  

  

• Casparian strip
  

  

8.1. Primary growth structure continued

• Rootcap, colummella, and quiescent center
  

  

• Exodermis
  

  

  • Lecture notes   B_note
    

    In most angiosperms, another layer of cells from casparian strips: the exodermis. Can prevent water loss. This can be continuous and fully suberized in plants form arid environments, or can be patchy and discontinuous. Passage cells are thin cells in exodermis that allow cross mebrane transport (especially Ca and Mg).

    More on Casparian strip. It is not just suberin. But other waxes as well as lignin as in secondary cell walls.

• Vascular arrangement: eudicots
  

  

• Vascular arrangement: monocots
  

  

• Endogenous branching
  
  • text   B_ignoreheading BMCOL
    

    Lateral roots break out through cortex.

  • figure   B_ignoreheading BMCOL
    

    

• Endogeneous branching
  

  

8.2. Secondary growth

• Completed primary growth
  

  

• In older root, epidermis dies
  

  Note aerenchyma!

  

• Origin of vascular cambium
  

  

• After formation of secondary phloem
  

  

• Epidermis and cortex being sloughed off
  

  

• After one year’s growth
  

  

8.3. Other roots

• Pneumatophores
  

  

• Prop roots in maize
  

  

• Aerial roots in epiphytes
  

  

• Aerial roots in epiphytes
  

  

• Storage roots: sweet potato, Ipomea batatas (Convolvulaceae)
  

  

• Cross section of Ipomea
  

  

• Modified roots: buttress roots
  

  

9.1. Primary growth

• Phytomeres
  

  

• Apical meristem: Tunica-corpus organization
  

  

• Coleus (Plectranthus spp, Lamiaceae)
  

  

• Coleus shoot tip
  

  

• Stem elongation
  

  Intercalary meristem

9.2. Vascular tissue arrangement

• Stem tissue organization
  

  

• Example: Tilia americana (Malvaceae)
  

  

• Example: Tilia americana (Malvaceae)
  

  

• Example: Tilia americana (Malvaceae)
  

  

• Example: Medicago sativa (Fabaceae)
  

  

• Example: Medicago sativa (Fabaceae)
  

  

• Example: Zea mays (maize)
  

  

• Example: Zea mays (maize)
  

  

9.3. Vascular connections

• Vascular connections
  

  

• Leaf and stem traces in an elm (Ulmus, Ulmaceae)
  

  

  • Lecture notes   B_note
    
    • Vascular bundles leading to brances or leaves cross the cortex and enter the branch of leaf.
    • Stem bundle and associated leaf traces are called a sympodium
    • Leaf traces: Often a median trace flanked by two lateral traces.
• Phyllotaxis (leaf arrangement)
  
  • Alternate
    
    • spiral (most common)
    • distichous
  • Opposite and whorled
    
    • opposite dicussate
    • whorled

10.1. Vascular connections

• Vascular connections
  

  

• Leaf and stem traces in an elm (Ulmus, Ulmaceae)
  

  

• Bristlecone pine - live vs dead vascular cambium
  

  

• Bristlecone pine - live vs dead vascular cambium
  

  

10.2. Leaf nomenclature and variation

• Leaf parts
  
  • text   B_ignoreheading BMCOL
    
    1. leaf apex
    2. Midvein
    3. Secondary vein
    4. Blade (portion between veins is lamina
    5. Leaf margin
    6. Petiole
  • figure   B_ignoreheading BMCOL
    

    

• Sessile leaves of a Moricandia species (Brassicaceae)
  

  

• Simple leaves
  

  

• Compound leaves
  

  

10.3. Leaf modifications

• Short-shoot long-shoot architecture
  

  Example: Fouqueria splendens (Ocotillo)

  

• Long shoot growth
  

  

• Petiolar spines forming from leaf midrib
  

  

• Short shoots
  

  

• Tendrils: Pea (Fabaceae)
  

  

• Cactus spines (Cactaceae)
  

  

  • Lecture notes   B_note
    

    Species: 1. Cylindropuntia imbricata, 2. Cylindropuntia prolifera, 3, 4. Cylindropuntia alcahes, 5, 6. Austrocylindropuntia vestita.

• Cactus spines (Cactaceae)
  

  

  • Lecture notes   B_note
    

    Cacti have small leaves on the main swollen stem, then spines which are modified leaves on a short shoot, so appearing in the axil of the usually deciduous leaf.

• Leaves on Opuntia (Cactaceae)
  

  

• Leaves on Opuntia (Cactaceae)
  

  

• Plant sharp parts
  

  Spines

  Modified leaves or part of leaf (eg modified stipules in Acacia and Prosopis)

  Thorns

  Modified stems

  Prickles

  Outgrowths of the cortex and epidermis

• Thorns on Ziziphus obtusifolia (Rhamnaceae)
  

  

• Prickles on Rosa
  

  

• Stipular spines ion Prosopis glandulosa (Fabaceae)
  

  

• Leaf variation: traps
  

  

• Bulb: Allium cepa (Amaryllidaceae)
  

  

  • Lecture notes   B_note
    

    Storage in fleshy leaves

11.1. Stem modifications

• Stem energy storage: Solanum tuberosum (Solanaceae)
  

  

• Stem photosynthesis Asparagus officinalis
  

  Cladophylls in asparagus (Asparagaceae)

  

• Stem water storage: Adenium obesum (Apocynaceae)
  

  

  • Lecture notes   B_note
    
    • Species native to Arabian peninsula
    • Also stems of many cacti.
• Corm: Crocosmia spp (Iridaceae)
  

  

  • Lecture notes   B_note
    

    Thickened stem with papery leaves covering it.

11.2. Leaf morphology

• Leaf anatomy overview
  

  Mesophyll

  specialized for photosynthesis. Palisade parenchyma and spongy parenchyma

  Epidermis

  Stomata, cuticle, trichomes

  Vascular bundles

  Smaller veins have bundle sheath cells, larger may be embedded in more sclerified tissue.

• Leaf anatomy
  

  

  Kelvin Ma 2014.

• Transverse cross section Syringia vulgaris (lilac, Oleaceae)
  

  

• Syringia vulgaris
  

  

• Transverse cross section Syringia vulgaris
  

  

• Paradermal section Syringia vulgaris
  

  

• Lower epidermis Syringia vulgaris
  

  

• Variation: a xeriphyte
  

  Nerium oleander (Apocynaceae)

  

  • Lecture notes   B_note
    

    Native to Mediterranean basin, planted widely around highways in US

• Variation: xeriphyte
  

  Nerium oleander (Apocynaceae)

  

• Variation: Nymphaea odorata (Nymphaceae)
  

  

• Variation: Nymphaea odorata (Nymphaceae)
  

  

  • Lecture notes   B_note
    
    • Water lily
• Maize stomata with subsidiary cells
  

  Stomata in grasses occur in rows

  

• Grass leaves: sugercane
  

  Kranz anatomy

  

• C3 grass: Poa annua
  

  

• C3 grass: Poa annua
  

  

• Pine needles (Pinus sylvestris, Pinaceae)
  

  

11.3. Leaf development and plasticity

• Leaf development
  

  

• Sun vs shade leaves
  

  Leaf size and shape is plastic, especially in response to light

  

• Sun vs shade leaves
  

  

  

• Aquatic and terrestrial leaves in Callitriche spp.
  

  

• Leaf abscission
  

  

12.1. Flower development

• Flower development from apical meristem
  

  Neptunia pubescens (Fabaceae)

  

• Flower development from apical meristem
  

  Neptunia pubescens

  

• Flower development from apical meristem
  

  Neptunia pubescens

  

• Flower development from apical meristem
  

  Neptunia pubescens

  

  • 5 stamen primordia
• Flower development from apical meristem
  

  Neptunia pubescens

  

• Flower development from apical meristem
  

  Neptunia pubescens

  

• Neptunia pubescens
  

  

  Photo by Bob Peterson

• Neptunia pubescens
  

  

12.2. Secondary growth

• Seasonal growth cycles
  
  • Plants are often characterized as
    
    • annuals
    • biennials
    • perennials (herbaceous or woody)
• Puya raimondii (Bromeliaceae)
  

  

  By Pepe Roque - Own work, CC BY-SA 3.0,

• Deciduous vs evergreen perennials
  

  Deciduous

  lose leaves during cold season (winter-deciduous) or dry season (drought-deciduous)

  Evergreen

  Have some leaves all year. But leaf lifespan can be very short (a month) or long (multiple years)

• Secondary growth
  
  • increases girth of plant body
  • occurs after primary growth and usually in second year/season of growth
  • occurs from two lateral meristems: The vascular cambium and the cork cambium
• Vascular cambium of stem
  

  

13.1. Vascular cambium

• Initials of the vascular cambium
  

  

• Periclinal divisions increase girth
  

  

• Sambucus canadensis transverse section
  

  

13.2. Periderm

• The cork cambium
  

  Makes the periderm composed of three parts

  • The cork cambium itself
  • Forms cork to the outside - suberin and wax layers, dead at maturity)
  • Forms phelloderm to the inside (resembles cortical parenchyma from primary growth)
• Tilia americana year one
  

  

• Tilia americana year two
  

  

• Tilia americana year three
  

  

• Lenticel in Aristilochea spp (Aristolochioideae)
  

  

  • Lecture notes   B_note
    

    Lenticels allow gas exchange.

• Bark, heartwood, sapwood
  

  

• Bark sloughs off
  
  • Older cork often sloughs off the outside of the tree
  • Older secondary phloem dies and sloughs off as well
  • How does the tree then keep producing periderm?
  • The cork cambium reforms deeper in stem over time!
    
• Tilia americana Multiple periderms example
  

  

• Cork oak
  

  

• Cork oak
  

  

  By Cazalla Montijano

• Cork oak
  

  By Alessandro Vecchi

• Leaf scars and terminal bud scars
  

  

• Bark variation: paper birch (Betula papyrifera)
  

  

  • Lecture notes   B_note
    

    Horizontal lines are lenticels

• Bark variation: shagbark hickory (Carya ovata)
  

  

• Bark variation: black oak (Quercus velutina)
  

  

13.3. Wood

• Wood types
  

  Softwoods

  Wood from conifers, a group of gymnosperms that includes the Pinaceae, Cupressaceae, Taxaceae and a few others.

  Hardwoods

  Most angiosperm (excluding the monocots!) wood

• Conifer wood: Pinus strobus (Pinaceae)
  

  

• Pit pair in Pinus strobus
  

  Margo-torus type pit common in conifer tracheids

  

• Angiosperm wood: Ulmus americana (Ulmaceeae)
  

  

• Ring-porous vs diffuse-porous angiosperm wood
  

  Quercus rubra (Fagaceae)

  

  • Lecture notes   B_note
    

    Ring prorous – large vessels in early wood only

• Ring-porous vs diffuse-porous angiosperm wood
  

  Liriodendron tulipifera (Magnoliaceae)

  

• Growth rings in Pinus longaeva
  

  

• Cross dating tree rings
  

  

• Branch bases are buried by secondary growth
  

  

• loose knots
  

  

  • Lecture notes   B_note
    

    If the branch dies and is engulfed, then there is no continuous connection between trunk and branch. cork rots off and we have a loose knot.

15.1. Phylogenies

• Phylogeny
  

  A phylogeny (“evolutionary tree”) is a branching diagram depicting evolutionary relationships among biological entities.

  

  • note   B_note
    
    • Phylogenies just depict evolutionary relationships and do not directly imply anything about morphology, traits, etc
    • Phylogenies can be rooted (usually how I will depict them in class) or unrooted. A rooted phylogeny implies a direction in which time operates along each branch. An “unrooted” phylogeny means that the true most ancestral node might by any of the internal nodes
• Phylogenetic terms
  

  

  • note   B_note
    
    • Phylogeny (the tree)
    • branch
    • node
    • leaf (or tip): corresponds to a taxon
    • polytomy (node with more than two descendant branches)
    • monophyly / monophyletic (group that contains all the descendants of a common ancestor and no others)
    • clade: a monophyletic group. We call two species that form a clade “sister species”
    • paraphyly / paraphyletic (non-monophyletic group that excludes descendents of common ancestor)
• Branches can be rotated around nodes without changing relationships
  
• Modern taxonomies attempt to name only monophyletic groups (clades)
  

  

15.2. Taxonomy and Phylogeny

• Naming
  

  Genus and specific epithet

  • Below species there can be
    

    subspecies

    eg Pinus contorta subsp. latifolia

    variety

    eg Cercocarpus montanus var. montanus

• Categories above genus
  

  Family

  (end in -aceae). Eg Poaceae

  (no term)

  Others: order, class, division (=phylum), kingdom…

  • But ranks have no real meaning!
    

    The name “Anthophyta” has meaning (=the angiosperms), but not the fact that it is a phylum/division

• Monophyly vs non monophyly
  

  

• How do we make phylogenies?
  

  We use traits to INFER the phylogeny

• Cladistics
  

  Use shared traits and assume parsimony

  

• Traits and phylogenies
  
  • Some traits define a monophyletic group. Homologous structures are those that have a common evolutionary origin.
  • analogous structures may be superficially similar but arose independently (eg fleshy stems and spines in Cactaceae, Euphorbiaceae, and Asclepidaceae.
• Convergent evolution
  

  Cactaceae Echinocactus texensis

  

• Convergent evolution:
  

  Euphorbiaceae: Euphorbia tetragona

  

• Molecular systematics
  
  • Many more more “traits” available (individual loci)
  • Can focus on potentially neutral regions of genome
• Chloroplast DNA
  

  

16.1. The Plantae

• Plantae phylogeny
  

  

• The green algae
  
  • Chlorophyceae
  • Ulvophyceae
  • Charophyceae (including Coleochaetophyceae on figure)
  • note   B_note
    

    Over 17,00 species in three major groups. All have cholroplasts similar to those of the land plants with both cholorophyll a and b and they all store starch in plasmids. Some have firm cell walls, others do not. They vary in cell division. The charophyceae are thought to be most closely related to the land plants. Alternation of generations occurs in some algae, but evolved independently in land plants

• Chlorophyceae
  

  

  • note   B_note
    

    Mostly freshwater, unicellular, flagellated

• Chlorophyceae life cycle in Chlamydomonas
  

  

• Ulvophyceae
  

  

  • note   B_note
    

    Mostly marine, multicellular. Ulva sea lettuce

• Some Ulvaceae have alternation of generations
  

  

  • note   B_note
    

    Isomorphic generations and also strains are similar, no egg and sperm.

• Charophyceae
  

  Coleochaete

  

  • note   B_note
    
    • Stoneworts (calcified cell walls in some)
    • freshwater or terrestrial
    • Some unicellular, others multicellular
    • Closest relatives of land plants
    • Have precursor of a cuticle
    • Some groups have sperm and egg producing organs
• Chara
  

  

• Chara
  

  

  • note   B_note
    

    Gametangia in Chara (top is oogonium, bottom is antheridium)

• Reproduction in stoneworts
  

  

  • note   B_note
    

    Not alternation of generations, but beginnings of embryo retention

• Alternation of generations
  
  • Text   B_ignoreheading BMCOL
    
    • Asexual reproduction:

    • Most animals reproduce this way:

    • Plants reproduce this way:
  • Figures   BMCOL B_example
    

    

  • Notes
    

    Alternation of generations

16.2. Life on land

• Plantae phylogeny
  

  

  • note   B_note
    

    Land plants = Embryophytes

• Major groups of land plants
  
  • Nonvascular plants: Bryophytes
    

    Liverworts, mosses, hornworts. All lack vascular tissue.

  • Seedless vascular plants
    

    Reproduce via spores (eg lycophytes, ferns, horsetails)

  • Seed plants
    

    Includes:

    • Non-flowering plants (the gymnosperms = “naked seed”)
    • Flowering plants. Angiosperms = “enclosed seed”
  • note   B_note
    

    If I use a name for a group without quotation marks (eg angiosperms), then that is an accepted monophyletic group. If I use quotes around a name then that is a historical name for a group that is not monophyletic or monophyly is uncertain. There can be disagreement – for example your textbook lists the historical bryophytes (mosses, hornworts, and liverworts) as non monophyletic but recent papers suggest that this group is monophyletic after all. Seed plants are monophyletic

• Major events in plant evolution
  

  Dates are approximate!

  700 mya

  Green algae: first plants with typical modern chloroplasts.

  475 mya

  Plants invade land

  400 mya

  Explosion of innovations — roots, overtopping growth (non dichotomous branching), vascular tissue

  350 mya

  Origin of seeds and wood (bifacial cambium)

  300-150 mya

  Diversification of the gymnosperm lineages

  150-50 mya

  Origin and diversification of angiosperms

  50-10 mya

  Origin and spread of recent groups like the grasses and cacti

  • note   B_note
    

    Get comfortable with some idea of relative time

• Innovations for life on land
  

  Group = the embryophytes. Origin around 475 MYA

  • Retained offspring (hence the name embryophyte)
  • Evolution of the cuticle and basic stomata
  • Way to protect spores from desiccation (sporopollenin)
• The Bryophytes
  

  They differ from the charophytes (stonewort algae):

  • Lecture notes   B_note
    
    • Presence of archegonia and antheridia
    • Multicellular diploid (sporophyte) stage and multicellular sporangia
    • Retention of zygote in archegonium of female gametophyte
    • Spores with cell walls containing sporopollenin
• The Bryophytes
  

  They differ from the “standard plant” you have learned about so far.

  • Lecture notes   B_note
    
    • Main plant generation is haploid
    • No true leaves, stems, or roots
    • main stem cannot branch
    • No xylem or phloem
  • note   B_note
    

    They have:

    • plasmodesmata
    • plastids
    • sperm are only flagellated cells
    • Spores germinate and grow into a protonema (plural protonemata), the juvenile sporophyte
    • Protective jacket around gametangia
    • growth from apical meristem.

    Spores germinate into “Protonemata” first. strandlike gametophyte, single cell wide. THese develope into thallus or more leafy structures.

• Relationship with other embryophytes under debate
  

  

• Relationship with other embryophytes under debate
  

  

  • Lecture notes   B_note
    

    Since early 2000s, there has been mounting evidence that extyan bryotphytes are monophyletic. This implies that liverworts LOST stomata.

17.1. Liverworts

• Relationship with other embryophytes under debate
  

  

  • Lecture notes   B_note
    

    Since early 2000s, there has been mounting evidence that extant bryotphytes are monophyletic. This implies that liverworts LOST stomata.

• Example: Riccia
  

  

  • note   B_note
    

    Leafy gametophyte is a thallus

• Epidermis and pores help prevent water loss
  

  

  • note   B_note
    

    Bryophytes have cuticle and pores. In mosses and hornworts, the sporophyte has true stomata, In liverworts these are not true stomata.

• Liverworts have male and female gametophytes
  

  

  • note   B_note
    

    Caplike antheridia produce sperm. Note also gemma cups which are vegetative reproduction of clones that splash out.

• Liverworts have male and female gametophytes
  

  

• Sexual reproduction in liverworts
  

  

• Some liverworts have airborne sperm
  

  https://www.youtube.com/watch?v=B-sFM0PhsX8

17.2. Mosses

• Reproduction in mosses
  

  

• Moss life cycle (example of Bryidae)
  

  

• Mosses (=Phylum Bryophyta in book)
  

  

  • note   B_note
    

    Sphagnum gametophyte with sporophyte

• Sphagnum sporophyte spore dispersal
  

  

  • note   B_note
    

    Dehiscent capsule. Dries and compresses air inside. Top flies off.

• Sphagnum “leaves” with hyaline cells
  

  

  • Lecture notes   B_note
    

    Hyaline cells (white in photo) are dead at maturity. Act as storage for water and nutrients. conducting tissue.

• Peat bogs (and fens, mires, etc)
  

  

  Photo by Merritt Turetsky (@queanofpeat)

• Peat harvesting
  

  

  • note   B_note
    

    Peat harvesting in Scotland

    @queenofpeat

• Other moss groups
  
  • granite mosses (Andreaidae)
  • “true” mosses (Bryidae)
• Some mosses have a strand of conducting tissue
  

  

• Some mosses have a strand of conducting tissue
  

  

  • note   B_note
    

    Hydroids lack protoplast at maturity, conduct water. Leptods are elongated cells that conduct sugars. Both have degenerate nuclei.

• Simplified stoma with single guard cell.
  

  

• Splash sperm dispersal in Polytrichum
  

  

• Spore dispersal in the Bryidae (“true” mosses)
  

  

17.3. Hornworts

• A Hornwort example: Anthoceros
  

  

  • note   B_note
    
    • Least diverse bryophyte group
    • Have sporophytes that have stomata when mature with two guard cells
    • Have some dichotomous branching
• A Hornwort example: Anthoceros
  

  

• A Hornwort example: Anthoceros
  

  

  • note   B_note
    

    Hornworts have unisexual gametophytes. Sporophytes have stomata, open longitudinally.

18.1. Vascular plant innovations

• More derived lineages reduce gametophyte generation and sporophyte becomes dominant
  

  

• Extant seedless vascular plants
  
  • Lycophytes
    
    • Isoetes (quillworts)
    • Club mosses (Lycopodiaceae) and spike mosses (Selaginellaceae)
  • Monilophytes
    
    • Wisk ferns (Psilotaceae)
    • Ferns
    • Horsetails (Equisetum).
• Origins of vascular tissue: tracheids
  

  

  • Note   B_note
    

    Importance of lignin in secondary cell walls. Lignin is a phenolic compound built from six-carbon rings.

• Stele types protostele, syphonostele, eustele
  

  

• Stele types protostele, syphonostele, eustele
  

  

• Microphylls and megaphylls
  

  

  • Lecture notes   B_note
    
    • microphylls: simple and linear, usually small, but can be multiple inches long (eg Isoetes). Associate with simple protostele of lycophytes
    • megaphylls: have venation of vascular tissue. Associated with syphonosteles and Eusteles
    • Microsteles probably originated as outgrowths, megaphylss as fused branch systems

18.2. Lycophytes

• Isoetes melanospora
  

  

• Lycophyte example: Lycopodium
  

  

• Selaginella (resurrection plant)
  

  

• Selaginella lepidophylla in Big Bend, Texas
  

  

  • Note   B_note
    

    Can completely dehydrate, “leaves” curl up into a tight dry brown ball. Hard to see on hillsides until after a rain.

• Selaginalla life cycle
  

  

  • Note   B_note
    
    • Heterosporous: megaspores and microspores.
    • Modified “leaves” around sporangia (microsprophyls, megasporophylls).
• Vascular plant phylogeny
  

  

  • Note   B_note
    

    Draw simplified version and show where traits evolved.

• Innovations: Upright growth and branching
  

  

  • Note   B_note
    

    From Donoghue 2005. Paleobiology 31(sp5):77-93. http://dx.doi.org/10.1666/0094-8373(2005)031[0077:KICASM]2.0.CO;2

    FIGURE 4. A comparison of sporophyte branching among early-branching lineages of land plants. In the bryophytic (moss) lineages (left) the sporophyte is unbranched; dichotomous branching evolved at the base of the polysporangiophytes (almost same point as evolution of vascular tissue) (center); overtopping (or pseudo-monopodial growth) evolved at the base of the euphyllophytes (right). Insets at the top represent these differences in branching at the level of the apical meristem. (Drawings at the bottom are from Stewart and Rothwell 1993.)

• Devonian lycophytes: secondary growth with unifacial cambium
  

  

  • Notes   B_note
    

    FIGURE 6. A sample of growth forms in extinct lycophytes. Two drawings on the left (from Phillips and DiMichele 1992) show early stages in the life cycle—establishment of the stigmarian “root” system with possibly photosynthetic “rootlets” prior to rapid stem elongation. Three drawings on the right (from Stewart and Rothwell 1993) show reconstructed forms of the determinate stems (not drawn to the same scale); from left to right: Sigillaria, Pleuromeia, and Lepidodendron.

• Unifacial vs bifacial cambium
  

  

  • Note   B_note
    

    From Donoghue 2005. Paleobiology 31:77-93. http://dx.doi.org/10.1666/0094-8373(2005)031[0077:KICASM]2.0.CO;2

    FIGURE 5. Differences between the bifacial cambium in the lignophyte lineage (including seed plants) and the unifacial cambium found in extinct tree lycophytes (e.g., Lepidodendron). The bifacial cambium produces both secondary xylem and secondary phloem, and the cambial initials are able to divide both periclinally (producing cells that differentiate in secondary tissues) and anticlinally (producing new cambial initials). The unifacial cambium produced only secondary xylem and the cambial initials divided only periclinally, limiting expansion of the cambial cylinder and the production of wood. These seemingly minor differences translated into major differences in evolutionary flexibility and “success”.

18.3. Monilophytes

• Wisk fern (Psilotum)
  

  

• fern example: Cyathea
  

  

• fern example: Adiantum
  

  

• Adiantum rhyzome
  

  

• Adiantum rhyzome
  

  

• Fern sori in Polypodium
  

  

• Fern sori in Pteridium aquilinum (Bracken fern)
  

  

• Fern sori in Polystichum
  

  

• Horsetails (Equisetum)
  

  

• Equisetum at White River rest stop
  

  

• Equisetum strobili
  

  

• Equisetum spores
  

  

• Equisetum stem with hollow pith
  

  

18.4. Age of the tracheophytes

• When did these innovations occur?
  

  

• “Trees” of the Devonian and Carboniferous
  

  

  • Notes   B_note
    

    FIGURE 7. Diversity of form among extinct treelike plants from the Devonian and Carboniferous (not drawn to the same scale). From left to right: Archaeopteris (an early lignophyte); Calamites (an equisetophyte); Psaronius (a marattialean “fern”), in which the trunk was formed by a mantle of adventitious roots; Tempskya (a filicalean “fern”), in which the trunk was formed by numerous smaller stems embedded in a tangle of adventitious roots.

• Early secondary growth and coal formation
  

  

  • Notes   B_note
    
    • Originally thought there was a delay in ligin degradation evolution but now we believe simply was climatic conditions suitable for no decomposition. https://www.pnas.org/doi/10.1073/pnas.1517943113

19.1. Seed plant phylogeny and innovations

• Phylogeny
  

  

• Key innovations
  
  • No reliance on water for fertilization
    
  • Seed (embryo + nutrient packet)
    

    An extreme form of heterospory

  • Bifacial cambium and wood
    

    Allows tall growth

• Evolution of the ovule (where seed is formed)
  
  1. Megaspore retained inside megasporangium (called nucellus in seed plants)
  2. Reduction to 1 megaspore mother cell per megasporangium and only one surviving megaspore.
  3. Female gametophyte intirely WITHIN megaspore and after fertilization, embryo also entirely within megasporangium
  4. Integument envelopes megasporangium except for one opening
• Ovule
  

  

  • Notes   B_note
    
    • Extreme form of heterospory
    • Megaspores retained in megasporangium (= nucellus)
    • One megaspore mother cell per megasporangium
    • Unequal division leads to one surviving megaspore daughter cell
    • Female gametophyte forms inside megaspore
    • embryo held in this female gametophyte
    • Megasporangium enclosed except for opening at end: micropyle
    • Conifer seeds contain cells from three generations of the tree. The nutritive tissues inside the seed are the haploid body cells of the female gametophyte. The seed also contains the developing diploid sporophyte. The the tough and protective seed coat is formed from the diploid cells of the parent sporophyte.
• Pollen
  

  

  • Notes   B_note
    
    • Microgametophyte. Very reduced. Can have different number of cells at dispersal stage

19.2. Pinophyta

• Pinophyta (Pines, firs, spruce)
  

  

• Pinus ponderosa
  

  

• Spruce and the Alaskan pipeline
  

  

• Lodgepole pine (Pinus contorta) cones
  

  

  • Note   B_note
    
    • Occur on separate cones on same tree
    • This species is common at high elevations across the western US. Some populations have serotinous cones that open following wildfire. This tree is often one of the first conifers to colonize wet meadows as it can withstand more waterlogged soil than can many other trees.
• Pine pollen grain: microgametophyte
  

  

  • Note   B_note
    

    Prothalial cells do not undergo any more mitosis and are only vegetative tissue of the microgametophyte (proto thallus)

    Generative cells will produce sperm, tube cell will produce pollen tube.

• Pine pollen grain
  

  

• Pine megaspores in female cone
  

  

  • Notes   B_note
    

    A bit like strobili of Equisetum

• Pine megaspores in female cone
  

  

  • Notes   B_note
    
    • Megasporocyte is mother cell of megagametophyte
    • No division of this cell takes place until AFTER pollination. This works out because it takes about 15 months for pollen tube to grow down and sperm nuclei to travel to egg!
    • Note no antheridia – male gametophyte has almost no structures.
    • See also [[https://en.wikipedia.org/wiki/Conifer_cone#/media/File:Pinus_{sylvestrisfemalestrobilusandconeen.svg}][]]
• Pine life cycle 1
  

  

• Pine life cycle 2
  

  

• Pine life cycle 3
  

  

• Pine life cycle 4
  

  

• Pine life cycle 5
  

  

• Pine life cycle 6
  

  

19.3. Gnetophyta

• Gnetophyta: Ephedra sp in Arizona
  

  

  • Note   B_note
    

    Three genera in this division: Ephedra, Gnetum, and Welwitschia. I took this photo of an Ephedra species in Walnut Canyon, Arizona near Flagstaff. But Ephedra antisyphilitica occurs right around Lubbock and we saw it on our field trip.

    Gnetum is found in tropics around the globe. Both Welwitschia and Gnetum havea type of double fertilziation but it forms a second embryo that aborts. As in other gymnosperms, the seed is nourished by gametophyte tissue, not an endosperm.

• Gnetophyta: Welwitschia
  

  

  • Note   B_note
    

    Photo: Thomas Schoch - http://www.retas.de/thomas/travel/namibia2003/index.html, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=650590

    Welwitschia is named after the Austrian botanist and doctor Friedrich Welwitsch who discovered the plant in 1859 in present-day Angola. Welwitsch was so overwhelmed by the plant that he, “could do nothing but kneel down and gaze at it, half in fear lest a touch should prove it a figment of the imagination.”

    Dr. Welwitsch abandoned medicine to study botany full time in 1839 and has life improved as a consequence.

19.4. Cuppressophyta

• Cupressophyta (Cuppressus, Juniperus, etc)
  
  • Photo   B_ignoreheading BMCOL
    

    

  • Text   BMCOL B_ignoreheading
    

    Giant Sequoia (Sequoiadendron gigantium)

• Giant sequoia cones
  

  

  #+BEAMER“ \tiny Photo: Didier Descouens

• Cuppressus (Cypress)
  

  

• Juniper and pinyon pine in New Mexico
  

  

• Juniperus “berry”
  

  

• Taxus (Yew)
  

  

  • Note   B_note
    

    Taxol was discovered in the late 20th century as an effective anti cancer substance for ovarian cancer and melanoma, but very little is in the tree. It can now be produced via cell lines in fermrentation tanks. paclitaxel is clinical name.

19.5. Ginkgo and Cycads

• Ginkgo biloba
  

  

• Ginkgo biloba male cones
  

  

  • Note   B_note
    

    Native to China but planted all over the world. The only species in the Division Ginkgophyta. Has good clonal (asexual) reproduction from basal buds or roots that form on damaged/drooping branches.

    The species is important in traditional Chinese medicine. The species is dioeceous.

    The sperm has multiple flagella and swims to the ovule after pollen lands on the stalk tip. See https://www.arboretum.harvard.edu/the-swimming-of-the-ginkgo-sperm/

• Ginkgo biloba female tree with ovules
  

  

• Ginkgo fertilization
  

  

• Ginkgo seeds and sperm
  

  

  • Notes   B_note
    
    • Both Ginkgo and Cycads have motile flagellated sperm. And in neither case is there a real pollen tube that takes sperm down to the egg.
• Cycads (Cycadophyta)
  

  

  Photo: Muhammad Mahdi Karim

• Cycads in Australia: Cycas brunnea
  

  

  Alastair Freeman, 2010

20.1. Overview

• Angiosperm reproduction overview
  

  

  • Notes   B_note
    
    1. perianth
       • sepals (calyx)
       • petals (corolla)
    2. stamens (androecium)
       • filament
       • anther two lobed = two pairs of pollen sacs
    3. carpel(s) (gynoecium)
       • ovary
       • style
       • stigma
• Angiosperm reproduction overview
  

  

• Angiosperm reproduction overview
  

  

• Angiosperm reproduction overview
  

  

20.2. Angiosperm life cycle

• Anthers
  

  

  • microsporocytes (diploid) in center,
  • tapetum is nutrient rich tissue around.
  • Other tissue forms wall of pollen sac
• Anthers
  

  

  • Notes   B_note
    
    • Heterosporous, as are all seed plants
    • Gametophytes reduced relative to even gymnosperms
    • Microspores formed in anthers, then they grow into two- or three-celled microgametophyte: pollen grain
    • so first microsporogenesis, then microgametogenesis.
• Pollen (the microgametophyte)
  

  

  • Notes   B_note
    
    • In some species, generative cell divides before pollen is dispersed, that results in three-celled pollen grain.
    • Pollen has inner wall (intine) and outer wall (exine). Thin places or holes in exine are sites for pollen tube initiation.
    • Sporopollenin coat is synthesized by the anther tapetum tissue and is a polymer of carotenoids
    • Protects pollen from UV, dehydration, pathogens
    • An additional coat is added by tepetum (pollen coat).
• Pollen grain example: Aesculus hippocastanum (Sapindaceae)
  

  

• Pollen grain example: Cucurbita pepo (Cucurbitaceae)
  

  

• Ovule structure
  

  

  • Notes   B_note
    
    • 7 cells, 8 nuclei. Surrounded by maternal tissue, the integuments. Two ends: chaalazal and micropyle.
• Formation of ovule
  

  

  • Notes   B_note
    
    • Most common megasporogenesis (a) involves:
    • diploid megasporocyte undergoes meiosis and results in 4 haploid megaspores. 3 disintegrate.
    • The megaspore nucleus then divides mitotically three times resulting in eight nuclei arranged in two groups of four.
    • Two migrate to center to form polar nuclei
    • cell walls form around three antipodals and also around egg and two synergids by egg nucleus. Result is 7 cells, 8 nuclei.
    • fitellaria type no cell walls during meiosis step.
    • oenethera type: ancestral. four cells, 4 nuclei at maturity.
    • Others have 8 cells, nine nuclei at maturity.
• Pollen tube
  

  

• Angiosperm life cycle: soybean
  

  

  • Lecture notes   B_note
    
    • endosperm divides mitotically
    • zygote develops into embryo with cotyledons
    • Integuments develop into seed coat
    • ovary wall develops into the fruit - many types
• Angiosperm life cycle: soybean
  

  

• Angiosperm life cycle: soybean
  

  

• Angiosperm life cycle: soybean
  

  

• Angiosperm life cycle: soybean
  

  

21.1. Floral variation

• Inflorescences
  

  

• Inflorescences
  

  

• Placentation
  

  

  • Notes   B_note
    

    Not shown are basal and apical placentation which can occur in simple ovaries with one locule.

• Ovary position
  

  

  • Notes   B_note
    

    Also known as “superior ovary”, having a hypanthium, “inferior ovary”

• Inferior ovary example: Malus domestica (apple, Rosaceae)
  

  

  • Lecture notes   B_note
    
    • domesticated apple
• Inferior ovary example: Malus domestica (apple, Rosaceae)
  

  

  • Lecture notes   B_note
    
    • 5, 5, many stamens.
    • 5 carpels. so how does this form one fruit?
• Floral symmetry
  
  • Radial (actinomorphic, regular)
  • Bilateral (zygomorphic, irregular)
• Flowers: perfect or imperfect
  

  Perfect flower

  functional stamens and functional stigmas

  Staminate flower

  functional stamens only

  Carpellate flower

  functional stigmas

• Plant sexes:
  

  which means that plants have several combinations

  Hermaphroditism

  perfect flowers only

  Monoecy

  staminate and carpellate flowers on same plant

  Dioecy

  Separate male and female individuals

• A dioecious plant: Cannabis sativa
  

  

21.2. Evolution of the angiosperms

• Angiosperm phylogeny
  

  

  • Notes   B_note
    

    Fossil pollen record to 135 MYA or so. Molecular clock dating goes back a bit further, to 140-180 MYA. By Middle Cretaceous of 100 MYA most major lineages exist.

    Five main “groups”

    • ANA grade (Amborella, Nymphales, Austrobaileyales)
    • Magnoliids
    • Monocots
    • Eudicots
• Amborella trichopoda
  

  

• Amborella trichopoda
  

  

  • Notes   B_note
    
    • Found only in rain forests of New Caledonia
    • Sister to all other angiosperms
    • That means it separated from them about 120-140 million years ago! It is the tip of a very long branch and we lack fossil information on its relatives.
    • It does have some archaic features, however:
    • Wood without vessels, only tracheids
    • flowers with tepals, stamens, carpels, spirally arranged in indefinite number
    • Unsealed carpels
    • But it has unisexual flowers and one seed fruits which different from what we believe early angiosperms had
• Nymphaceae
  

  

  • Lecture notes   B_note
    
    • You can see these in Texas!
    • four celled embryo sacs, diploid endosperm
    • indefinite (can vary) number of floral parts, all separate
• Austrobaileya scandens
  

  

  • Notes   B_note
    
    • There are other Austrobaileyales including star anise (Illicium anisatum)
    • These early groups all show the third megagametophyte patterns where there is a single polar nucleus and therefore a diploid endosperm.
    • ancestral traits: tepals, stamens with innermost sterile (Separate stamens from carpels) then many carpels. 12-15 carpels each with 8 to 12 ovules
• Magnoliid: Liriodendron tulipifera
  

  

• Magnoliid: Magnolia grandiflora
  

  

  • Lecture notes   B_note
    

    There are about 20 magnoliid families, many only in southern hemisphere.

• Trends in Angiosperm floral evolution
  
  • Many and indefinite flower parts to few and definite
  • Axis shortened and floral parts fused
  • Inferior ovary in more derived groups
  • Radial symmetry to bilateral symmetry
• Lonicera (Caprifoliaceae, in the Asterid group)
  

  

• Gossypoium (Cotton, Malvaceae)
  

  

• Asteraceae: Helianthus annus
  

  

• Disk and ray flowers
  

  

  • Lecture notes   B_note
    

    Ray flowers also called “ligulate flowers”

• Cirsium pastoris (Asteraceae)
  

  

• Agoseris (Asteraceae)
  

  

• Orchidaceae
  

  

• Platanthera limosa
  

  

  https://northamericanorchidcenter.org/featured-orchids-of-southwestern-us/

21.3. Animals and flowers

• Coevolution with animals
  

  

• Rodent pollination in Proteaceae
  

  

  • Note   B_note
    

    Protea in the Proteaceae. Southern hemisphere (Gondwanan) plant family. Compound inflorescence head like in asters. Specialized pollen presenting styles that spring up.

• Rodent pollination
  

  

  • Note   B_note
    

    Johnson, C. M., & Pauw, A. (2014). Adaptation for rodent pollination in Leucospermum arenarium (Proteaceae) despite rapid pollen loss during grooming. Annals of botany, 113(6), 931–938. https://doi.org/10.1093/aob/mcu015, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3997634/

    See also a nice summary at https://www.indefenseofplants.com/blog/2018/9/24/rodents-as-pollinators

• Fly pollination in Stapelia schinzii (Apocynaceae)
  

  

• Insect vs wind pollination
  

  

• Heterostyly in Lythrum salicaria (Primulaceae)
  

  

  • Note   B_note
    

    See Eckert et al 1996: https://www.nature.com/articles/hdy1996185

• Distribution of types becomes more even over time
  

  

• Colors not aimed at us
  

  

• Pollination through deception
  

  

• Pollination through deception
  

  

• Flower coloration
  
  • Carotenoids (in plastids)
    
  • Flavonoids
    
    • Anthocyanins (in vacuoles)
    • Flavonols
  • Betacyanins
    

    In the Caryophyllales (eg Cactaceae)

22.1. Fruit types

• The fruit
  

  Mature ovary and possible accessory tissue

  • Simple fruits
    

    Single carpel, or multiple united carpels

  • Aggregate fruits
    

    Separate carpels that each mature but stay together in dispersal

  • Multiple fruit
    

    Whole inflorescence forms a single fruit

• Major fleshy fruit types
  
  • Berry. Multiple seeds
  • Drupe. One seeded.
  • Pome. Compound inferior ovary
• Berry: Eg Solanum lycospersicum (Solanaceae)
  

  

• Drupe: Eg Prunus spp.
  

  

• Pome: Pyrus spp.
  

  

• Major dry fruit types
  
  • Dehiscent
    
    • legume (one carpel), follicle (one carpel), silique (two carpels)
    • capsule: multiple carpels
  • Indehiscent
    
    • achene (and similar cypsela in Asteraceae), including samaras
    • grain (caryopsis)
    • nut
    • schizocarp
• Capsule and silique
  

  

• Legume: Bean (Phaseolus spp)
  

  

• Loculicidal capsule on Yucca
  

  

• Yucca shidigera
  

  

• Yucca moth pollination
  

  

• Yucca moth pollination
  

  

• Achene, samara, cypsela, and caryopsis
  
  •    BMCOL
    

    

  •    BMCOL
    

    

  • Lecture notes   B_note
    
    • Achene and samara and cypsela: pericarp connected to seed coat just at funiculus so it can peel off
    • cypsela is term for the achene-lie fruit of a asteraceae (inferior ovary)
    • samara is a winged achene
    • caryopsis is a grain: grasses. pericarp fused to seed coat over entire surface.
• Nut: hazelnut, Corylus (Betulaceae)
  

  

  • Lecture notes   B_note
    

    Nuts have stony and thick pericarp. Usually form from compound ovary with one functional carpel.

• Pecan, Carya illinoinensis (Juglandaceae)
  

  A drupe!

  

• Nutmeg and mace, Myristica fragrans (Myristacaceae – a Magnoliid)
  

  

• Myristica fragrans
  

  

• Multiple carpels
  

  

  • Lecture notes   B_note
    
    • Can lead to simple fruit like a pone, or a berry
    • Aggregate fruit: multiple ovaries in single flower. Blackberry fruit of druplets
    • Aggregate accessory fruit: Strawberry. Achenes on fleshy receptacle
    • Multiple fruit: Multiple flowers merge. Pineapple is example. The “cones” of some proteaceaae

22.2. Dispersal

• Wind dispersal
  

  

• Animal dispersal: Phorodendron
  

  

  • Lecture notes   B_note
    

    seed is sticky in many mistletoes. Sticks to anus of the bird who must scrape it off.

• Dispersal by ants: elaiosomes
  

  

• Inflorescence as dispersal unit: Xanthium
  

  

23.1. Overview

• Questions:
  
  • What is the most abundant protein on the planet?
  • Why is the global atmospheric CO2 level higher in January and lower in June?
  • Can plants photosynthesize in the dark?
• Most important biochemical reaction on the planet
  

  In its current form (O₂ producing), evolved nearly 3 billion years ago in cyanobacteria.

• The great oxygenation event
  

  

• Global atmospheric C0₂
  

  

• CO₂ over time
  

  

• CO₂ over time
  

  

  • Lecture notes   B_note
    

    Fig 4 from Foster, G., Royer, D. & Lunt, D. Future climate forcing potentially without precedent in the last 420 million years. Nat Commun 8, 14845 (2017). https://doi.org/10.1038

• Sunlight to carbohydrate
  
  • Simplified equation
    

    CO₂ + H_2O + Light Energy → CH₂O + O₂

  • note   B_note
    
    • Is the process of using sunlight to produce carbohydrate
    • Requires sunlight, carbon dioxide, and water
    • Produces oxygen as a by-product
• Photosynthesis vs respiration
  
  • Photosynthesis is endergonic
    

    Reduces CO₂ to sugar

  • Cellular respiration is exergonic
    

    Oxidizes sugar to CO₂

• Where does the oxygen come from?
  
  • Some bacteria produce sulfur, not O\(_2\)
    

    CO₂ + 2 H₂S + Light Energy → (CH₂O) + 2 S

  • Using labeled O\(_2\)
    

    CO₂ + 2 H₂¹⁸O + Light Energy → (CH₂O) + H₂O + _¹⁸O

• Less simple equation
  
  • Water on both sides of equation
    

    3 CO₂ + 6 H₂O + Light Energy → C₃H₆O₃ + 3 O₂ + 3 H₂O

• Chloroplasts
  

  u

• Chloroplast structure
  

  

• Two linked reactions
  

  

• Short term energy storage: ATP and NADPH
  
  • ATP   BMCOL
    

    

  • NADPH   BMCOL
    

    

  • note   B_note
    

    These modified nucleotides have covalent bonds with high energy

• Longer term energy: glucose
  

  

  • note   B_note
    

    Glucose is moved through the plant, but longer term energy is stored as starch (eg in tubers in roots to overwinter). Glucose is also used to make cellulose, the main structural material in the plant.

• Harvesting light energy
  

  First step is to produce a hydrogen (H+) diffusion gradient by splitting water into O\(_2\) and hydrogen (protons)

23.2. Light reactions

• Electromagnetic spectrum
  

  

  • note   B_note
    

    Blue light has more energy than red light

• How to get useful energy from light?
  
  • It must be absorbed by pigments
    
  • note   B_note
    

    Because leaves are mostly green, they must be absorbing light in red and blue portions of spectrum.

• Absorption
  

  Two major pigment classes in plant leaves: Chlorophylls (a and b) and Carotenoids (carotenes and xanthophylls)

  

  • note   B_note
    

    Chlorophylls are most important pigments to photosynthesis. But it turns out others can extend the range of wavelengths that are useful by passing energy on to chlorophyll. Also, another role of pigments like carotenoids is quenching free radicals and protecting chlorophyll from damage.

• Chlorophyll a
  

  

  • Lecture notes   B_note
    

    A chlorophyll molecule consists of a porphyrin head (four pyrrole rings containing nitrogen arranged in a ring around a magnesium ion) and a long hydrocarbon tail. The hydrocarbon tail is lipid-soluble.

• Photosystems
  

  Chlorophyll molecules work together in groups

  • A photosystem consists of two major elements:
    
    1. An antenna complex
    2. A reaction center

    as well as proteins that capture and process excited electrons

  • Photosystem complexes
    
    • A photosystem + additional light harvesting complexes
• Photoexcitation
  

  

  • note   B_note
    

    Excited electrons in chloroplasts may

    • Drop back down to a low energy state, causing fluorescence
    • Excite an electron in a nearby pigment, inducing resonance
    • Be transferred to an electron acceptor in a redox reaction
• Two types of reaction centers:
  
  • Photosystem II
  • Photosystem I

  These photosystems work together: electron output of II is electron input to I. They are linked by a enzyme complex: Cytochrome

  • note   B_note
    

    Photosynthesis increases dramatically when cells are exposed to both red and far-red light simultaneously. The fact that photosynthetic rate is higher under both light sources than the sum of the rates under each light source individually is known as the “enhancement effect”. This indicates a coupled set of processes.

• Z-Scheme
  

  

  • Note   B_note
    

    Here is a video describing the light reactions: https://www.youtube.com/watch?v=hj_WKgnL6MI

• Electron transport chain
  
  • Electrons captured by electron acceptors in PSII and used to power proton pump
  • Electrons excited again in PSI and eventually transferred to NADP+

  

  • Lecture notes   B_note
    
    • Plastoquinone
    • cytochrome b6f
    • FNR= Ferrodoxin NADP reductase
• Review: steps in storing chemical energy
  
  1. Sunlight excites electrons in reaction centers
  2. Energy in excited electrons used to split water to release protons (H+) and O\(_2\)
  3. This creates a hydrogen ion (H+) diffusion gradient.
  4. Diffusing H+ powers ATP production. NADPH is produced in second electron transport chain in PSI
• Cyclic photophosphorylation
  

  PSI only

  

  • Note   B_note
    
    • Previous discussion was all about noncyclic photophosphorylation.
    • Electron transport back to photosystem I center rather than being passed to NADP+
    • This drives transport of H+ into lumen of thylakoid, adding to H+ gradient and allowing greater ATP synthesis.

24.1. Rubisco and photorespiration

• Rubisco
  

  

  • note   B_note
    

    Fixes C02 to RuBP

• Limitations on photosynthesis
  

  

• Carboxylase and Oxygenase
  

  Rubisco is also an oxygenase — when O₂ concentration is high compared to CO₂, rubisco binds to RuBP and O₂

• Content of atmosphere
  

  This is the problem:

  • 78.1% N₂
  • 20.9% O₂
  • 0.9% Ar
  • 0.04% CO₂
  • 0.002% Ne
• Atmospheric CO₂ concentration through time
  

  

• Photorespiration: chloroplast
  

  

• Photorespiration: perixosome and mitochondria
  

  

25.1. C4 Photosynthesis

• When is photorespiration a problem?
  
  • When atmospheric CO₂ is low
  • When internal CO₂ is low (stomata narrowed to prevent water loss)
  • When light and temperature are higher
  • How to avoid photorespiration?
    

    Increase CO₂ concentration around RuBisCO by using a non oxygenase in initial carbon acquisition step: PEP carboxylase (Phosphoenolpyruvate carboxylase)

• C4
  

  

  Gurevitch et al 2004

• Anatomy of a C3 leaf
  

  

  Gurevitch et al 2004

• C4 leaf: spatial separation of light rx and carbon aquisition
  

  

• C4 Plants: Sugarcane
  

  

• C4 Plants: Maize
  

  

• C4 Plants: Blue grama
  

  

  Copyright Curtis Clark

  • Image copyright note:   B_note
    

    “Bouteloua gracilis 2004-08-22” by Copyright by Curtis Clark, licensed as noted - Photography by Curtis Clark. Licensed under CC BY-SA 2.5 via Commons - commons.wikimedia.org

• Advantages of C4:
  
  • Higher maximum rates of photosynthesis
  • Higher temperature optimum
  • Higher water use efficiency
  • Higher N use efficiency
• C4 CO2 response
  

  

• C4 photosynthesis
  
  • evolved up to 50 times independently
  • present in 19 angiosperm families
  • only 3% of angiosperm species are C4
  • But they account for 20% of earth’s total primary production
• Atmospheric CO₂ concentration through time
  

  

• When did C4 evolve?
  

  

  Figure: Osborne and Sack 2012

  • note   B_note
    

    See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3248710/

• Distribution of C4 grasses in North America
  

  

  Figure: Gurevitch et al 2004

• When does C3 outperform C4?
  

  

• Where does one find C4 plants?
  
  • Warm climates with some productivity (not too dry).
  • But not so productive that trees overtop grasses!
  • So landscapes like the southern High Plains where there is a warm and reasonably wet summer, but rainfall variability or total rainfall limits trees
  • Or semi-tropical grasslands where fire limits trees
• Carbon isotopes useful for detecting past vegetation from paleosoils
  

  

  • Lecture notes   B_note
    

    Higher δ¹³C values indicate organic material created by C4 photosynthesis. δ¹³C = {(R of sample / R standard) - 1} X 1000 . Carbon 12 is about 99 percent of C in atmosphere.

• Subtropical grasslands
  

  

• Spread of C4 occured well after evolution of C4!
  

  

  • Note   B_note
    

    Late miocene shift to grasslands

• What controls C4 grass distribution today?
  

  

• What happened in the Miocene that allowed expansion of C4 vegetation?
  
  • Increased aridity
  • Increased seasonality
  • Increased fire (charcoal evidence)

25.2. CAM Photosynthesis

• Crassulacean Acid Metabolism (CAM)
  
  • Problem
    
    • CO₂ acquisition leads to water loss
    • Daytime air is dry (low relative humidity).
  • Solution
    
    • Store carbon to separate light reactions and Calvin cycle in time.
• Temporal separation: night
  

  

• Temporal separation: day
  

  

• Where do you find CAM plants?
  

  Over 30,000 species

  • Desert succulents (Cactaceae, Agavaceae, Euphorbiaceae)
  • Tropical epiphytes (Bromeliads, some orchids)
  • Some aquatic plants (??!!)
• CAM plants: Euphorbia tetragona
  

  

• CAM plants: Cactaceae (Echinocactus texensis)
  

  

• CAM plants: Agave neomexicana
  

  

• CAM plants: Bromeliads
  

  Tillandsia in Florida

  

  photo: Hans Hillewaert

• CAM plants: Aquatic? Isoetes
  

  

  Figure: Wikimedia commons AHR 2013

  • Note
    

    CAM photosynthesis has also been found in a few aquatic plants. What value would it serve for such plants? See http://www.jstor.org/stable/4354319

• Types of photosynthesis
  

  

26.1. Key Concepts and overview

• Transpiration
  

  

• Plants balance root water acquisition with transpiration
  
  • Nearly all water loss is to the atmosphere
  • Nearly all water gain is via roots
  • All other sources negligible (metabolic water gain, loss in photosynthetic reaction)
• Stomata
  

  

• Water is pulled up the plant through xylem tracheids and vessels
  
• Water moves up the plant and down a potential energy gradient
  
  • Driven by
    
    1. Loss to dry air
    2. Water concentration differences (osmotic forces)
    3. Matric forces (adhesion, cohesion)
    4. Pressure
    5. Gravity
• Major forces moving water
  
  • Loss to dry air
    

    Function of the relative humidity (usually measured as Vapor Pressure Deficit, VPD)

  • Osmotic gradients
    

    Water moves from region of high to lower water concentration.

    

  • Pressure gradients
    

    Both positive (pressure) and negative (tension).

• Water can be under tension (negative pressure)
  

  Hydrogen bonds allow cohesion of water molecules to one another and adhesion to charged surfaces.

  figs/water-tension.pdf

26.2. Water in air

• Water in air
  

  Water vapor is one component of air

  Water vapor pressure

  Denoted \(e\). Partial pressure of water vapor in atmosphere. Measured in pressure units (eg KPa) or in relative volume (cm³ / m³). This is “absolute humidity”.

  Saturated vapor pressure

  Denoted \(e_0\). Partial vapor pressure when liquid and gas phase of water are at equilibrium. Temperature dependent.

  VPD and RH

  Vapor Pressure Deficit (VPD) and Relative Humidity (RH) are two ways of describing the amount of water in air relative to the saturation vapor pressure.

• Saturation vapor pressure
  

  figs/vapor-pressure.pdf

• Why is water pulled from leaves?
  
  • Transpiration
    

    Results from water moving from high concentration (inside leaf) to low (dry air)

    • Vapor pressure deficit (VPD):: \(e_0 - e\). Difference between saturated vapor pressure and actual vapor pressure. Depends on actual amount of water in air and on temperature
    • Relative humidity (RH):: \(\frac{e}{e_0} \times 100\)

    Whenever VPD is non zero (when RH < 100%), then the atmosphere can potentially pull water from leaves!

• Saturation vapor pressure and VPD
  

  figs/vapor-pressure2.pdf

26.3. Water potential

• Water potential
  
  • Water potential (\(\Psi\)) is
    

    The potential energy of water per unit volume in a particular environment relative to pure water at atmospheric pressure (defined as \(\Psi = 0\))

  • Differences in water potential
    

    determine how water moves: Water always flows from higher to lower water potential

• Water potential is sum of components
  

  Ψ = Ψ_osmotic + Ψ_matric + Ψ_vapor + Ψ_pressure + Ψ_gravity

  • Different components are important at different points in soil-plant-atmosphere continuum:
    

    soil

    matric and some osmotic

    plant

    osmotic and pressure (tension). Gravity of minor effect in tall plants

    atmosphere

    vapor

• \(\Psi\) is in units of pressure
  

  

• Cohesion-tension theory of water transport
  

  

  • Note   B_note
    

    We usually us megapascals (MPa) as the units of water potential. One MPa is about 145 pounds per square inch of pressure. This means that a well watered plant with a turgid leaf may have leaf mesophyll cells at around 210 pounds per square inch of pressure (\(\Psi_{pressure}\) = 1.5 MPa). A desert shrub during drought might have xylem vessels at -7 MPa, which is just over 1000 lb/in\(^2\) !

• Water potential from soil through plant
  

  Soil to plant

  \(\Psi_{osmotic}\) of root cells must be lower than \(\Psi_{matric}\) of soil water to draw water into roots.

  Within the plant

  \(\Psi\) at any point \(\Psi{}_{solutes} + \Psi{}_{pressure}\)

  Root cells to xylem vessels

  \(\Psi_{pressure}\) of xylem must be lower than \(\Psi\) of root cells

  Xylem vessels to leaf cells

  \(\Psi_{osmotic}\) of leaf cells must be low to draw water from xylem

  Transpiration

  Leaf cells to atmosphere is driven by very low (NEGATIVE) \(\Psi\). Eg -100 MPa.

• Turgor pressure
  

  When pressure inside the cell (turgor pressure) increases, the cell wall pressure is induced. A cell that is firm is turgid

  

• A turgid cell can still have negative water potential
  
• Loss of turgor = Wilting
  

  

• Measuring water potential
  

  

• “Pressure Bomb”
  

  

27.1. Water uptake and soil water

• Symplast and apoplast
  
  • Remember that xylem tissue is primarily dead cells
  • And live plant cells have plasmodesmata
  • Symplast
    

    Everything within the cell membrane

  • Apoplast
    

    Almost everything outside the cell membrane (xylem, water space in cell walls, water-filled spaces between cells).

• Water entry into roots
  

  Water must get from soil through epidermis and cortex tissue to vascular tissue

  

• Root endodermis
  

  

• The Casparian strip
  

  Narrow band of wax on endodermal cells. Composed of suberin.

  

  • Note   B_note
    

    This hydrophobic band forms a barrier to water. It forces water into symplast at endodermis – across cell membrane. This allows plants to control ion uptake.

• Soil water: matric forces
  

  

• Salt scalding
  

  

• Salt scalding
  

  

• Predawn vs midday water potential
  
  • During the night, VPD drops and stomata are closed (for C3/C4)
  • Therefore, flow stops and Ψ equilibrates
  • Predawn water potential then indicates something about soil water potential
• Example: Mesquite
  

  

• Example: Juniper
  

  

• Water potential question:
  

  During late summer you measure leaf water potential pre-dawn in a juniper and mesquite growing side by side. You find that the predawn Ψ for the juniper is -5 MPa and for the mesquite it is -2 MPa.

  • Which has deeper roots?
    
    • A) Mesquite
    • B) Juniper

27.2. Xylem and cavitation

• Tracheid pits
  

  

• Bordered pit pairs in a conifer tracheid
  

  

• Xylem vessel elements
  

  

  • Note   B_note
    

    B: Shows early vessels (Magnolia) to more derived on right (oak). Trend is towards wider.

• Besides wilting, what happens when water potential gets too low?
  

  

• Drought dieback: Davis Mtns, Texas
  

  

• Drought mortality: Santa Rosa Mtns, California
  

  

• Cavitation video   B_note
  

  https://www.youtube.com/watch?v=YzpDN7laepo

27.3. Plant adaptations to drought

• Whole plant adaptations
  
  • Drought avoidance whole plant (desert annuals)
  • Drought avoidance through phenology: drought deciduous (deserts and Mediterranean shrublands)
  • Drought tolerance:
    • Desiccation avoidance: High root-shoot ratios, succulents
    • Desiccation tolerance requires specific xylem anatomy)
• Whole plant adaptation examples
  
  \begin{overlayarea}{10cm}{7cm} \centering \includegraphics<1>[height=7cm]{figs/namaqualand.jpg} \includegraphics<2>[height=7cm]{figs/amboy.jpg} \includegraphics<3>[height=7cm]{figs/ocotillo.jpg} \includegraphics<4>[height=7cm]{figs/buckeye.jpg} \includegraphics<5>[height=7cm]{figs/Velvet_mesquite.jpg} \includegraphics<6>[height=7cm]{figs/horse_crippler.jpg} \end{overlayarea}
• Anatomical adaptations
  
  • Desiccation avoidance:
    
    • Stomatal number, size and arrangement, control
    • Isobilateral leaves (symmetrical internal architecture, amphistomatous: stomata on both sides of leaf
    • Waxy cuticle or hairs
    • Curl or fold leaves
  • Desiccation tolerance:
    
    • Extreme xylem resistance to cavitiation
    • Narrow vessels?
    • Ability to resprout following dieback
• Nerium oleander
  

  

• Anatomical adaptation example: stomatal crypts
  

  

27.4. Drought in West Texas

• Quercus hypoleucoides
  

  

• Quercus grisea
  

  

• Xylem vulnerability curves
  

  

  1 MPA = 145 PSI! See https://dl.dropboxusercontent.com/u/69724712/reprints/Schwilk%2BBrown%2Betal-2016.pdf

28.1. Water and sugar

• Phloem
  
  • Translocation is the movement of sugar through the plant
  • Occurs via phloem sieve-tube elements and companion cells.
• Phloem
  

  

• Compartmentalized in vascular bundles
  

  

• Pressure-flow
  

  

• Phloem parasites
  

  

  • Note   B_note
    

    Aphids pierce phloem and pressure pushes sap through them. Honeydew is sap excreted. Some ants “tend” aphids (clip wings, produce chemical intoxicant to drug them).

28.2. Plant hormones

• Hormones
  
  • Greek “hormon” means to stimulate
  • Chemicals that are active in small quantitied
  • Induce a response to control a physiological event — regulate.
• Major hormone groups
  

  Auxins

  control apical dominance, differentiation of tissues, abscission, flowering, fruit development…

  Cytokinins

  Produced mostly in roots, travels through xylem to shoot, con control apical dominance and leaf senescence

  Ethylene

  Gas produced in multiple tissues. Huge effect on fruit ripening.

  Abscisic acid

  Made in leaves and roots in response to stress. Important in stomatal closure, also important in many dormancy mechanisms.

  Gibberelins

  Control cell elongation, seed germination, stimulation of flowering

  Brassinosteroids

  Act locally near point of synthesis. Wide range of effects

• Auxins: polar transport
  

  

  • Lecture notes   B_note
    

    Charles Darwin performed experiments published in 1881. Power of movement in plants. Grass seedlings. bent toward light only if tip (apical meristem) was exposed to light. But bending occurred in cell elongation further down the coleoptile.

    In 1926 Frits Went named the substance “Auxin” (Indole-3-acetic acid).

• Auxins
  
  • Produced in shoot, travels polarly down towards roots
  • Indirectly inhibits axilary bud growth
  • Promotes lateral root formation
  • promotes expansion of vascular cambium in woody plants
• Apical dominance and auxins
  

  

  • Lecture notes   B_note
    

    Draw.

• Auxins in fruit
  

  Produced by developing seeds

  

  

• Cytokinins (example, Nicotiana tissue on agar)
  

  

• Ethylene
  
  • Fruit ripening
  • shoot growth behavior changes in response to stress

29.1. Tropisms

• Gravitropism
  

  

• Sensed via amyloplasts settling to lower side of cell
  
  • In shoots: in statocyte cells in the starch sheath (innermost cortical cells)
  • In roots: rootcap — cytokinin produced on lower side of root tip and that inhibits cell elongation.
• Root tip with free cytokinin in blue
  

  

• Other tropisms
  
  • hydrotropisms in roots
  • thigmatropism (eg pea tendrils).

29.2. Timing of physiology

• Circadian rhythms
  
  • 24-hour internal clocks continually entrained (reset) by environment (eg day/night)
  • Control flower opening and closing (eg Datura)
  • Leaf movement
  • Control sensitivity to particular hormones (gating)

  http://plantsinmotion.bio.indiana.edu/plantmotion/movements/leafmovements/clocks.html

• Photoperiodism
  

  Day length controls flowering in many plants

  

• Measuring day length
  

  Plants don’t measure day length, they measure darkness!

  Karl Hamner and James Bonner in 1938: cocklebur, a short day plant

  • Found that a single leaf was enough to sense day length.
  • discovered a single minute of light during the night STOPPED the flowering response of the short day.
• Lettuce seed experiments with red and far red light
  

  Lactuca sativa seeds need light to germinate. Red light works best (660 nm). Far red light can inhibit germination even better than darkness

  • Experiment with flashes of light:
    
    • red light, then far red: no germination
    • red, far red, red: germination:
    • red, far red, red, far red: no germination
    • red, far red, red, far red, red: germination
• Phytochrome: two forms
  

  

• Phytochrome: two forms
  

  

• Phytochrome and shade/neighbor detection
  

  

• Day length and latitude
  

  

• Vernalization and stratification
  
  • many plants will only flower if the plant is first exposed to a cold period
  • many seeds will only germinate if they are first cold stratified
• Nastic movements
  

  

• Sensitive plant (Mimosa pudica)
  

  

30.1. Allocation

• Life history characteristics
  

  Control allocation to and timing of reproduction and growth

  • Age at first reproductive event
  • Reproductive lifespan and age-specific mortality rates
  • Number and size of offspring
• Life span
  
  • Annuals (\(\approx 21\%\) of N.A. species)
  • Biennials (\(\approx 2\%\) of N.A. species)
  • Perennials (\(\approx 77\%\) of N.A. species)
• Variation in life history
  
  • sexual versus asexual reproduction (clones)
  • frequency of reproduction:

    iteroparous

    Reproducing more than once

    semelparous

    Reproduce once and die

• Semelparous example, Agave paryi
  

  

• Life expectancy
  

  Variations in the life expectancy are related to the probability that an adult survives from one year to the next.

• In unpredictable environments we find more annuals}
  

  

30.2. Seeds and seedbanks

• When should an annual set seed?
  

  Fecundity schedules in annuals often reflect predictability of the end of the growing season

  predictable

  Reproduction delayed until near the end of season (main meristem transformed into reproductive tissue)

  unpredictable

  Reproduction begins as soon as plants have attained some minimal size (often axillary

• Buffering populations against stochasticity
  
  • Seed banks
    

    If environment is constant, seeds should germinate immediately. However environment often is variable in time.

  • Long lived persistent individuals
    

    Adults can often survive environmental conditions unsuitable to establishment and can thus buffer population against environmental stochasticity.

• Seed germination: Predictable vs unpredictable environments
  

  Light

  Indicates no shading by competitor.

  Soil moisture

  in some environments, rainfall at germination predicts subsequent rainfall.

  Fire

  A good predictor that subsequent environment will be free of established competitors and high in nutrients

• Phenology
  
  • Vegetative phenology
  • Reproductive phenology

30.3. Annual vs perennial

• Annual vs perennial?
  

  Cole’s Paradox. Lamont Cole (1954)

  • \(p\) = fraction of plants that survive each year to reproduce
  • \(F\) = number of seedlings produced by each plant per year
  • Then perennial’s fitness \(\lambda_p = p(F_p+1)\)
  • Annual’s fitness \(\lambda_a = pF_a\)
• Annual vs perennial continued
  

  Charnov and Schaffer (1973)

  Added possibility that survival from seed to adult was different probability.

  • \(c\) = Fraction of first year plants (seeds) that survive
  • Then perennial’s fitness \(\lambda_p = cF_p + p\)
  • Annual’s fitness \(\lambda_a = cF_a\)
  • Annuals should be more fit when \(F_a > F_p + \frac{p}{c}\)
• Demography and life history
  

  

30.4. Life history strategies

• Past approaches to defining “strategies”}
  
  • r vs K-selection
  • Broad groups (annual, perennial, herb, shrub, etc)
  • Grime’s triangle — everyone loves triangles!
• r vs K-selection
  
  • Logistic growth
    

    \(\frac{1}{N}\frac{dN}{dt} = r(\frac{K-N}{K})\)

  • Prediction (MacArthur and Wilson 1967,1972):
    

    At low population densities, selection should favor traits that increase r. At high densities, selection should favor traits that raise K.

• Grime’s C-S-R triangle
  

  

31.1. See blackboard pdf files

• See blackboard PDF files
  

  under “resources/fire ecology lecture slides”