Plant Reproduction

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Chapter 38

• Plant Reproduction

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Sexual Reproduction
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Flowers Reproductive Organs of Plants

• Four parts
• Sepals
• Petals
• Stamens
• Contains the anther pollen producers
• Carpels
• Ovary contain one or more ovules

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Flowers cont.

• Stamen and carpels contain sporangia
• Develop into the gametophytes
• Pollen grains male gametophyte
• Embryo sac female gametophyte
• Fertilization occurs when male and female
  gametophytes meet
• Pollen lands on the stigma, pollen tube is
  formed, and sperm is released into the embryo sac
• Seed and fruit form after fertlization

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Flower variations

• Complete flowers contain all four parts
• Incomplete flowers missing one of the four
  parts
• Bisexual Flower perfect flower has both
  stamens and carpels
• Unisexual flower missing one or the other
• Monoecious plant has both male and female
  flowers
• Dioecious plant has only male or female flowers

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Development of Male Gametophyte

• Anther contains sporangia, each sporangia
  contains diploid microsporocytes
• Microsporocytes undergo meiosis to form four
  haploid microspores
• These give rise to the pollen grain (male
  gametophyte)

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Development of Male Gametophyte

• Microspores divide once by mitosis and produce
  two cells
• Generative cell produces sperm
• Tube cell produces the pollen tube
• All enclosed by thick resistant wall and forms a
  pollen grain

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Pollen Formation
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Development of Female Gametophyte

• Ovule contains a megasporocyte
• Divides through meiosis and forms four haploid
  megaspores
• Only one megaspore survives
• Divides through mitosis three times producing a
  cell with 8 nuclei
• This cell then seperates the nuclei into
• Egg cell
• 2 synergids
• 3 antipodal cells unknown function
• Polar nuclei 2 nuclei not partitioned and share
  cytoplasm with large central cell of embryo sac

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Self-fertilization

• Plants have many mechanisms to reduce selfing
• Improves genetic variability
• Dioecious plants cant self-fertilize
• Bisexual flowers different flowers mature at
  different times
• Self-incompatibility rejects its own pollen

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Self-incompatibility
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Fertilization Process

• Double fertilization pollen grain generative
  cell divides by mitosis producing two sperm cells
• One sperm cell fertilizes the egg and the other
  joins the polar nuclei forming the endospore
  (food storing cell)

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Endosperm Development

• Triploid (3n) endosperm forms a milky substance
  used as food for the growing embryo

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Embryo Development
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Structure of Mature Seed

• Seed coat is formed from the ovules integuments
• Embryo
• Hypocotyl
• Radicle

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Fruit Development

• Developed from mature ovaries of plants
• Protects the seed and aids in dispersal of the
  seed
• Wall of ovary becomes the pericarp
• Outer covering of the fruit

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Seed Germination

• Seed dormancy
• Insures the seed germinates at an advantageous
  time
• Seed to Seedling

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Asexual Reproduction

• Fragmentation portion of the parent plant
  breaks off and becomes a new plant
• Sometimes the root will form a new plant
• Apomixis seed production without fertlization