Plant Sexual Reproduction

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Plant Sexual Reproduction

• Chapter 38
• 6th Edition Big Campbell

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Sexual Reproduction in Plants
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Angiosperm Life Cycle

• Sporophyte
• The flower
• Dominant generation
• Diploid form
• Result of union of gametes

• Gametophyte
• Within the anthers and ovaries
• Depend of sporophyte parents
• Haploid form
• Gametes (sperm egg)

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• During Sexual Reproduction in Plants
• Fertilization occurs in the ovary
• In the ovary is the development of the seeds
  which contain sporophyte embryos
• Ovary becomes the fruit
• Ovule (inside ovary) becomes the seed

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Reproductive Organs of Plants

• Stamen male anther (pollen grains produce
  sperm)
• Carpal female ovary, stigma (landing platform
  for pollen), style, ovule (inside the ovary
  contains the embryo sac which produces the egg)

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In order for Fertilization to Occur

• Pollen is released and lands on stigma
• Each pollen grain produces a pollen tube which
  grows in the ovary through the style
• Sperm released into the embryo sac (egg)
• Embryo grows
• Ovule develops into a seed
• Ovary becomes fruit
• Fruit dispersal will spread seeds
• Seedlings will grow and produce new generations
  of sporophytes (flowering plants)

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Floral Organs

• Complete Flowers
• Have all four organs sepals, petals, stamen,
  carpals
• A.K.A. Bisexual Flowers
• Has stamens and carpals

• Incomplete Flowers
• Lacking 1 or more organs
• A.K.A. Unisexual Flowers
• Missing either carpal or stamen

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• Monoecious Species
• A plant that has staminate or carpellate flowers
  on same plant

Dioecious Species A plant that has staminate and
carpellate flowers on separate plants
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Gametophytes - Male

• Pollen Grain
• One microsporocyte (inside pollen sac) forms four
  haploid microspores
• The microspores then divide by mitosis to produce
  a generative cell and a tube cell
• Generative cell will form 2 sperm when lands
• Tube cell produces the pollen tube

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Gametophytes - Female

• Embryo Sac
• In the ovary, in the ovule, in the sporangium
  there is a megasporocyte that divides by meiosis
  to make 4 haploid megaspores
• The megaspore divides three times to form
• 3 antipodal cells (unknown function)
• 2 synergids (aid pollen tube in finding eggs)
• 1 egg
• 2 polar nuclei (not divided into individual cells
  share the cytoplasm of the central cell in sac

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Preventing Self Fertilization

• Dioecious plants are unisexual and therefore
  cant fertilize themselves
• Self-Incompatibility the plant can reject its
  own pollen (Figure 38.8)
• A biochemical block provents pollen from
  fertilizing
• Similar to animals immune system in which foreign
  material is rejected, except here the self
  material is rejected

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Double Ferilization

• 1 sperm fertilizes the egg to form the zygote
• 1 sperm combines with two polar nuclei to form a
  triploid nucleus
• This large triploid cell gives rise to ENDOSPERM
  (food storage tissue of the seed)

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Embryo Development
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Embryo DevelopmentFigure 38.10
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Mature Seed

• Hypocotyl embryonic axis
• Radicle - embryonic root
• Epicotyl portion of the axis above the
  cotyledons

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The Ovary Becomes a Fruit

• The fruit protects the enclosed seeds and aids in
  their dispersal
• Fruit develops only if pollination and
  fertilization are successful
• The fruit ripen the same time as the seed
  development is complete
• Apples oranges are exaggerated versions of the
  fleshy fruit variety
• Wheat rice are also fruits with a pericarp that
  adheres tightly to the single seed within

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Development of a pea pod
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Seed Dormancy

• An adaptation of seedling survival
• Condition of low metabolic rate and temporary
  suspension of growth and develop
• Dormancy is broken after a specific environmental
  cue is given
• Cues could be temperature, substantial rainfall,
  intense heat by fire, extended exposure to cold,
  certain hours of daylight, or chemical attack by
  an animals digestive system
• Cues are different for every species of plant

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Nutrients During Germination

• The seed imbibes water (uptake of water due to
  low water potential of the seed)
• Embryo releases gibberellin (hormone) which
  signals growth of the aleurone
• The aleurone secretes enzymes to hydrolyze food
  in the endosperm
• The nutrients are absorbed by the scutellum and
  consumed by the embryo

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Emerging Seedling

• First to emerge is the radicle
• Next, shoot tip will break through soil surface
• Hypocotyl starts as a hook shape and when
  stimulated by light it straightens and raises the
  cotyledons
• The epicotyl will emerge its first true leaves
  and photosythsis begins
• The cotyledons will shrivel and fall away, their
  food reserve has been consumed

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Your Assignment

• Take notes on the Asexual Reproduction of Plants
  (pages 794 797)
• Take notes on Plant Biotechnology
• (pages 797 799)
• Quiz at the beginning of the period tomorrow on
  all diagrams