Unit 7.4

• Plant reproduction

  • Two-stage, alternating life cycle
  • Sporophyte produces haploid spores by meiosis
  • Spores divide mitotically to become haploid gametophytes
  • Gametophytes produce gametes
  • Gametes fuse to produce a diploid zygote
  • Zygote divides mitotically to become the diploid sporophyte

  
• Microspore

  Male gametophyte
• Megaspore

  Female gametophyte
• Flowers

  • Flowering occurs in response to environmental signals such as day length
  • Monocots have flower parts in threes and multiples of three
  • Eudicots have flower parts in fours or fives and multiples of four or five
  • Typical flower has four whorls of modified leaves attached to a receptacle at the end of a flower stalk called a peduncle
• Sepals

  Protect the bud
• Petals

  Attract pollinators
• Stamens

  • Male portion of flower
  • Anther - Saclike container
  • Filament - Slender stalk
• Carpel

  • Female portion of flower
  • Stigma - Enlarged sticky knob
  • Style - Slender stalk
  • Ovary - Enlarged base enclosing ovules

  
• Flower types

  • Complete flowers
  • Incomplete flowers
  • Perfect (bisexual) flowers
  • Imperfect (unisexual) flowers
  • Monoecious plants
  • Dioecious plants

  
• Male gametophyte development

  1. Microspores produced in anthers

  2. Microspore mother cells undergo meiosis to produce microspores

  3. Microspores undergo mitosis to produce pollen grains

  
• Female gametophyte development

  1. Ovary contains one or more ovules

  2. Megaspore mother cell undergoes meiosis to produce four haploid megaspores, three of which are nonfunctional

  3. Functional megaspore divides mitotically until there are eight nuclei in the female gametophyte (embryo sac)

  4. Embryo sac contains egg cell, two synergid cells, central cell with two polar nuclei, and three antipodal cells

  
• Pollination

  1. Transfer of pollen from anther to stigma

  2. Self-pollination

  3. Cross-pollination
• Fertilization

  1. Pollen grain germinates, forming a pollen tube

  2. Pollen tube passes between stigma and style to reach micropyle of ovule

  3. Double fertilization - one sperm nucleus unites with egg nucleus, other sperm nucleus unites with polar nuclei

  
• Seed

  Mature seed contains embryo, stored food, and seed coat
• Eudicot embryo development


  1. Zygote divides repeatedly to form proembryo and suspensor

  2. Globular stage - proembryo is a ball of cells

  3. Heart and torpedo stages - embryo becomes heart-shaped then elongates to torpedo shape

  4. Mature embryo - epicotyl contributes to shoot, hypocotyl contributes to stem, radicle is embryonic root

  
• Monocot vs eudicot seed structure

  • In monocots, cotyledon stores nutrients and absorbs from endosperm
  • In eudicots, cotyledon stores all nutrients embryo will need

  
• Fruit


  Mature ovary
• Fruit types

  • Simple fruits
  • Compound fruits - aggregate fruits, multiple fruits
• Pericarp

  • Ovary wall that thickens to become the fruit
  • Exocarp - outermost skin
  • Mesocarp - fleshy tissue
  • Endocarp - boundary around seeds
• Dry fruit types

  • Dehiscent - splits open when ripe
  • Indehiscent - does not split open when ripe

  
• Seed dispersal

  • Dry fruits dispersed by wind
  • Fleshy fruits attract animals for food dispersal
• Seed germination


  • Embryo resumes growth and metabolic activity
  • Requires oxygen, adequate temperature, and moisture

  
• Vegetative reproduction

  • New plant grows from fragment of parent or specialized structure
  • Includes stolons, rhizomes, cuttings, grafting, layering
• Tissue culture

  • Growth of tissue in artificial liquid or solid medium
  • Plant cells are totipotent - can become entire plant
• Somatic embryogenesis

  Hormones stimulate development of plantlets from leaf or other tissue
• Somaclonal variation

  Mutations leading to new plants with desirable traits
• Meristem tissue

  Results in clonal plants with identical traits
• Anther tissue culture

  Haploid cells in pollen grains cultured to produce haploid plantlets, then chemically doubled to diploid
• Cell suspension culture

  Rapidly growing calluses cut into small pieces and shaken in liquid nutrient medium, used to extract chemicals and metabolites