Plant Growth and Reproduction

Growth

• Growth is the increment in dry mass, volume, length, or area resulting from the division, expansion, and differentiation of cells.
• Plant growth can be analyzed by looking at the increase in total plant dry mass and its distribution (allocation) among organs involved in the acquisition of above-ground and below-ground resources.

Growth Analysis of Plants

• Absolute Growth Rate (AGR): (W2 – W1)/(t2 – t1)
• Relative Growth Rate (RGR): (lnW2 – lnW1)/(t2 – t1)

Factors Influencing RGR

• RGR = LAR x NAR
  • LAR = leaf area ratio = amount of leaf area per unit of total plant mass
  • NAR = net assimilation rate = rate of increase in plant mass per unit leaf area, largely the result of the rate of carbon gain by photosynthesis, carbon lost by respiration, and allocation of carbon to roots, stems, and leaves.
• RGR is a function of the net rate of carbon gain and the patterns of allocation.

Plant Growth

• Plants grow from localized regions of cell division called "meristems".
• Shoot apical meristem
  • Internode
  • Axillary bud meristem
  • Node
  • Apical bud
  • Leaf primordia
  • Lateral buds with axillary meristems
• Cork cambium
• Vascular cambium
• Lateral root meristem
• Root apical meristem
  • Root hairs
  • Vascular cambium
  • Vascular tissue
  • Root cap

Primary vs. Secondary Growth

• Apical meristems increase height.
  • Shoot tip (shoot apical meristem and young leaves)
  • Epidermis
  • Primary phloem
  • Primary xylem
  • Axillary bud meristem
  • Root apical meristems
• Lateral growth meristems
  • Vascular cambium
  • Root system
  • Cork cambium
  • Lateral meristems increase girth.
  • Vascular cambium
  • Primary phloem
  • Secondary phloem
  • Primary xylem
  • Secondary xylem

Herbaceous vs Woody Plants

• Herbaceous (non-woody) plants grow only from apical meristems and consist of primary growth.
• Woody plants contain tissues derived from both primary and lateral meristems and exhibit primary and secondary growth
  • Secondary xylem (wood): sapwood vs. heartwood
  • Vascular cambium (lateral meristem)
  • "Bark" = secondary phloem + cork cambium + cork

Modular Organisms

• Plants are modular organisms: they grow by producing repetitive units
• Rhizomatous growth in Carex bigelowii (Jonsdottir & Callagham 1988)
  • Genets
  • Ramets
  • Rhizome = underground horizontal stem
  • Adventitious roots = roots originating from non-root organs (e.g., stems)
  • Tillers = shoots (modules) in grasses and grass-like plants.

Clonal Growth

• Clonal Growth (aka vegetative reproduction)
  • A clone of Prairie Sandreed (Calamovilfa longifolia)
  • A clone of Plateau live oak (Quercus fusiformis)

Clonal Growth and Plant "Foraging"

• Phalanx
  • Greater branching
  • "Intensive" foraging
• Guerilla
  • Minimal branching
  • "Extensive" foraging
  • Rhizomes
  • Soil surface

Plant Reproduction

• Asexual reproduction
  • Clonal growth (stolons, rhizomes)
  • Agamospermy (apomixis) = asexual seeds
• Sexual reproduction
  • Seedless plants (ferns)
  • Seed plants
    • Gymnosperms = “naked” seeds; cones
    • Angiosperms = enclosed seeds; flowers & fruits
• Dandelions (Taraxacum sp.)

Sexual Reproduction in Angiosperms

• Lily flower
  • Petals and sepals = perianth
  • Anther
  • Stigma
  • Style
  • Stamen
  • Filament
  • Carpels/pistils = gynoecium
  • Stamens = androecium
  • Ovule
  • Developing pollen grain
  • Haploid nucleii
  • Ovary
  • Ovary wall
• Pollen lands on stigma surface, pollen tube emerges and grows down style, sperm cells are carried through pollen tube to ovules inside ovary.
• After fertilization, the ovules and their contents swell and develop into seeds.
• The stigma, styles, stamens, sepals, and petals wither, shrink, and fall off.
• The ovary swells and becomes fruit.
• When the fruit is mature it will open and release the seeds.

Pollination Ecology

• Pollination vs. Fertilization
• Pollen Vectors
  • Abiotic
    • Wind (Anemophily)
    • Water (Hydrophily)
  • Biotic
    • Insect (Entomophily)
    • Birds (Ornithophily)
    • Bat (Chiropterophily)
• Facultative and Obligate Pollination Types
• Mutualism: plant/animal benefits
• Coevolution: Yucca and its moth pollinator

Wind Pollination

• Flowers dull color
• Reduced perianth
• Abundant pollen
• No nectar
• No odor
• Grasses; many trees (willows, oaks, elms)

Beetle Pollination

• Variable, but dull flowers
• Strong, fruity odor
• Flat to bowl-shaped flowers
• Nectar: none or open
• Pollen or food bodies

Fly Pollination

• Purple, brown, or greenish flowers
• Strong smell of decay
• Flowers flat or deep trap
• Nectar: none or open
• Often no food

Bee Pollination

• Flower color: variable but not red
• Sweet odor
• Flowers flat to moderate; often broad tube
• Nectar: present, often concealed
• Nectar guides

Butterfly Pollination

• Flower color: variable, pink is common
• Moderately strong smell
• Deep, narrow tube flowers; upright
• Nectar: present, often concealed
• Nectar guides

Moth Pollination

• Nocturnal
• Color: white, pale, or green
• Strong sweet smell
• Deep floral tube, often pendant
• Abundant nectar, concealed
• Often no landing platform

Bird Pollination

• Flowers vivid, often red/scarlet
• No odor
• Tubular flowers, w/o lip
• Nectar very abundant, concealed
• Flower wall hard, ovary protected

Bat Pollination

• Nocturnal
• Flowers whitish to drab, purple
• Strong odor at night
• Robust flowers, large mouth
• Nectar very abundant; also much pollen
• Flowers hang away from foliage

Plant Mating Systems

• Plants have many different mating systems
  • Obligate outcrossers (self-incompatible)
  • Selfers (self-compatible)
  • Hermaphrodites
    • Protandrous
    • Protogynous
  • Monoecious
    • Staminate flowers
    • Pistillate (carpellate) flowers
  • Dioecious
    • Staminate plants
    • Pistillate plants

Seed Dispersal: Abiotic Agents

• Dandelion seed (Taraxacum)
• Maple fruit (Acer saccharum)

Seed Dispersal: Biotic Agents

• Cocklebur fruit (Xanthium strumarium)
• Mistletoe berries (Phoradendron leucarpum)
• Clark's Nutcracker: seed caching

Seeds and Dormancy

• Seed = embryo + endosperm + seed coat
• Dormancy = state of suspended activity; alive but very low respiration rates
• Dormancy mechanisms
  • Physical (hard seed coats; scarification)
  • Chemical inhibitors
  • Light & Temperature (stratification)
  • Dimorphic seeds
• Radical = young root

Seedling Ecology

• Germination:
  • Breaking of dormancy
  • Imbibition & swelling
  • Resumption of growth
• Seedling establishment
  • Successful germination and growth
  • The most critical phase in a plant’s life cycle
• Seed banks: pool of dormant seeds in the soil
• Seed rain: input of seeds into the seed bank