Ch. 7: Plant Growth and Reproduction

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Ch. 7 Plant Growth and Reproduction
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Terms

• Flower parts (BIOL 1030)

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Floral variation

• Parts may be fused
• Example, petals fused to each other.

Snapdragon flower
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Floral variation

• Fusing of petals can form floral tube (nectar
  made at bottom)
• Only long-tongued or long-billed pollinators can
  reach it.

Aesculus pavia flowers
seed
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Floral variation

• Flowers with both stamens and pistils perfect
  flowers
• Some flowers imperfect. Either pistillate (have
  pistil) or staminate (have stamens).

Pistillate flowers of Sagittaria
Staminate flowers of Sagittaria
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Floral variation

• Note some species make pistillate flowers and
  carpellate flowers on separate individuals
• This termed dioecious (MUST outcross to reproduce
  sexually)
• Monoecious is when both sexes on same individual.

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Floral variation
Persimmon fruits

• Example of dioecious species Persimmon
  (Diospyros virginiana)

Pistillate flower
Staminate flower
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Floral variation

• Some flowers are missing one or more sets of
  basic parts incomplete flowers
• Note that all imperfect flowers are therefore
  incomplete!

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Floral variation

• Some flowers assembled into groups of flowers
  inflorescence
• Special inflorescence type head
• Example, sunflower and its relatives
• Ray flowers have large fused petals (corollas
  fused), disk flowers small and crowded.

ray flowers
disk flowers
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Floral variation

• Flowering dogwood (Cornus florida)
• Inflorescence white structures are modified
  leaves (bracts) that act like petals.

Closeup showing individual greenish flowers
Inflorescence
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Pollination

• Why flowers so varied? Many form mutualism (,
  interaction) with animals to achieve pollination

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Terms

• Pollination (flowering plants) transfer of
  pollen from anther to stigma

Carpelpistil
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Terms

• Fertilization occurs when sperm in pollen tube
  made by pollen grain fuses with egg in ovule to
  produce zygote

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Pollination

• Abiotic pollen carried by wind or water
• Wind pollination common among grasses, temperate
  zone trees (Quercus, Carya, Pinus)
• Not a mutualism

A grass
Carya
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Terms

• Biotic pollination pollen carried by animal
• About 90 of flowering plants

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Terms

• Floral visitor animal that visits a flower
• Pollinator animal that deposits pollen on stigma
  from compatible flower
• All pollinators are floral visitors, but not vice
  versa!

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Terms

• All pollinators are floral visitors, but not vice
  versa!
• How decide?
• 1) Careful observation of visitor morphology and
  activity

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Terms

• How decide?
• 2) Single visit study
• Bag flower bud, allow flower to open
• Remove bag, allow visitor to make 1 visit
• Re-bag flower and see how many seeds result
• Can use to compare effectiveness of different
  pollinator species

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Pollination as Mutualism

• Most flowering plants are pollinated by animals
• This is mutualism (,) interaction
• Plant gets pollen transferred
• Animal gets reward

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Animal Rewards

• Pollen high in protein
• Also has lipids, minerals, starch

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Rewards

• Can be renewed by
• sequential anther dehiscence (multiple stamens)

Tony Danzas Masters Study
Creosote bush
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Rewards

• poricidal anthers (buzz pollination) anthers
  have holes at tip

Vaccinium (blueberry)
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Rewards

• Nectar sugary fluid produced by nectar glands
  (nectaries) in flower

Lonicera japonica
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Rewards

• Nectar 10-60 sugars
• May have amino acids too (butterfly flowers)
• Renewable reward!

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Rewards

• Oils/Resins
• some used as construction materials
• cologne (male solitary bee uses oil as female
  attractant)
• food for larvae (Krameria)

Krameria wax gland wasp food!
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Rewards

• Edible petals (pineapple guava New Zealand)

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Pollination

• Benefits of animal pollination for plant
• 1) Directed dispersal of pollen pollen taken
  directly to stigma of another flower. Results in
  gene flow
• Record distance for insect pollination?

20 km! For tropical orchid
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Pollination

• How does animal know where to go?
• Floral cues and attractants
• Color and shape
• Scent
• Warmth (thermogenic plants rare)

Skunk cabbage
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Pollination

• Benefits of animal pollination for plant
• Directed dispersal aided by learning of floral
  visitors decreases handling time
• Fosters floral constancy (visiting single
  species on foraging trip) by bees

Bumblebee visits to touch-me-not
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Pollination

• Benefits of animal pollination
• 2) Style of flower as selective racetrack
• Keep in mind that 1 pollen grain can fertilize 1
  ovule
• Suppose 5 pollen grains arrive on stigma
• Start to make pollen tubes
• How many can fertilize an ovule?
• 2! First 2 to arrive!
• Rest? LOSERS!

Pollen grains
stigma
style
ovary
2 ovules
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Pollination

• Benefits of animal pollination
• 2) Style of flower as selective racetrack
• Pollen tubes are haploid (1N)
• Haploid means only 1 allele (gene version) for
  every trait
• If an allele is recessive, then it will be
  expressed (cant be masked by another, dominant
  allele)
• So, fittest (fastest) pollen grains mate
• Inferior genes dont get passed to offspring.

Pollen grains
stigma
style
ovary
2 ovules
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Pollination

• Style of flower as selective racetrack
• Is there evidence that this works?
• Example, Coyote melon
• Gourd growing in U.S. deserts.

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Pollination

• Style of flower as selective racetrack
• Study done in 2000 showed that
• 1) takes 900 pollen grains to fully pollinate
  flower
• 2) 1 pollinator visit puts 650 grains/flower. By
  2 hours, 4000 grains deposited on stigma
• 3) Seeds produced from over-pollinated flowers
  produced more vigorous seedlings (compared to
  seeds from flowers with
  stigma).

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Outcrossing

• Major benefit of sexual reproduction generate
  genetic variation
• This enhanced by mating with others (outcrossing)

Why just enhanced?
Making gametes by meiosis 23 pairs of
chromosomes gives 6 million different
combinations of Moms and Dads chromosomes in
gametes
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Outcrossing

• How to favor outcrossing
• 1) Dioecy

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Outcrossing

• How to favor outcrossing
• 2) Floral morphology
• Heterostyly Flowers differ in stamen/style
  length
• Distyly Two different morphs of perfect
  flowers, each type on a different plant

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Outcrossing

• Ex, Gelsemium sempervirens

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Outcrossing
Protandry

• How to favor outcrossing
• 3) Floral phenology
• Protandry anthers dehisce first
• Protogyny stigma becomes receptive first

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Outcrossing

• How to favor outcrossing
• 4) Self-incompatibility prevents germination of
  self pollen or slows self pollen tube growth