Plant Reproduction

1
Plant Reproduction
2
Alternation of Generations

• Mosses - gametophyte is the dominant form of the
  plant
• Ferns, gymnosperms and angiosperms - sporophyte
  is the dominant form of the plant

3
Sexual reproduction in angiosperms

• Flower parts
• sepals - outer whorl or ring
• protect the other parts of the developing
  flower
• petals - next whorl
• animal pollinated plants have brightly
  colored petals
• wind pollinated plants usually have small
  or absent sepals/petals

4

• Stamens - next whorl male reproductive
  structures
• consist of
• -anther (produce microspores that develop
  into pollen grains)
• -filament (supports the anther)

5

• Carpels - innermost whorl female reproductive
  structures
• pistil (one or more fused carpels)
• -ovary - enlarged base of pistil
• -style - stalklike
• -stigma -top, sticky or with hairs to trap
  pollen grains

6
Gametophytes develop within the reproductive
structures

• -female gametophyte (embryo sacs) form within the
  ovary of the pistil
• Megasporangium surrounded by two integuments,
  each with a micropyle
• -contains a megaspore mother cell, which
  undergoes mitosis to produce four haploid
  megaspores
• -one megaspore undergoes three mitotic
  divisions, which produces a cell with eight
  haploid nuclei

7

• -one nuclei from each end (pole) migrate to
  center and become polar nuclei
• -one cell nearest to micropyle enlarges and
  become the egg
• -two cells on either side of egg help attract
  pollen tube toward the egg
• -the integuments and embryo sac are now a mature
  ovule, which may develop into a seed

8

• -male gametophyte (pollen grains) form within the
  anthers of the stamens
• An anther contains four microsporangia (pollen
  sacs)
• -microspore mother cells each produce four
  haploid microspores
• -each microspore undergoes mitosis to produce
  two haploid cells that do not separate (pollen
  grain)
• -the larger of the two cells is the tube cell
  (forms pollen tube)
• - the smaller of the two cells is the generative
  cell, which will divide by mitosis to form two
  sperm

9
Pollination

• -occurs when pollen grains are transferred from
  an anther to a stigma
• -self-pollination - involves one flower, flowers
  on the same plant, or flowers from two
  genetically identical plants
• -cross-pollination - involves two genetically
  different plants

10

• -self-pollinated due to structure of flower
• -pollen dispersed by water
• -pollen dispersed by air (wind)
• depends on
• release of large amounts of pollen
• ample air circulation
• proximity of plants to which pollen is
  transferred
• dry weather

11

• -pollinated by animals
• -have bright flowers, distinctive odors, nectar
  (sugar solution)
• -pollinators include bats, bees, beetles, moths,
  butterflies, mosquitoes, monkeys, and hummingbirds

12
Fertilization

• -union of haploid gametes resulting in diploid
  zygote
• -a pollen grain must land on a stigma, absorb
  moisture, and germinate (form a pollen tube)
• -pollen tube grow through stigma and style toward
  the ovary
• -enter ovule in ovary through micropyle

13

• -two sperm travel through pollen tube and reach
  the egg
• -double fertilization is unique to angiosperms
• one sperm fuses with the egg to form diploid
  zygote
• one sperm fuses with two polar nuclei, and then
  eventually develops into endosperm (provides
  nourishment for the embryo)

14
Dispersal of fruits and seeds

• Fruits and seeds are dispersed by
• -animals (carried or eaten)
• -wind (tiny or with parachutes)
• -water (contain air chamber)
• -forcible discharge (pod dries and breaks
  open)
• -gravity

15
Fruit types

• A fruit is a mature ovary.
• Fruits protect seeds, aid in their dispersal, and
  delay sprouting of seeds.
• Classified based on
• -how many pistils or flowers form the fruit
• -whether the fruit is dry or fleshy
• p. 619 Table 30-1

16
Structure of seeds

• A seed is a plant embryo surrounded by a
  protective coat called the seed coat.
• Seed structure differs between monocots, dicots,
  and gymnosperms.
• -dicot - two cotyledons which store nutrients
  (no endosperm)
• plumule - shoot tip with embryonic leaves
• epicotyl - between plumule and cotyledons
• hypocotyl - cotyledons to radicle
• radicle - embryonic root

17

• -monocot - one cotyledon and endosperm
• absorbs nutrients from endosperm
• -gymnosperm - sporophyte embryo with needle-like
  cotyledons, surrounded by the tissue of the
  female gametophyte which functions as a source of
  nutrients for the embryo

18
Seed germination

• A seed will not germinate (sprout) until it is
  exposed to certain environmental conditions.
• Many seeds experience dormancy (a state of
  reduced metabolism growth and development do not
  occur).

19

• Conditions needed for germination
• -water - softens seed coat, activates enzymes
  that convert starch in cotyledons into simple
  sugars
• -oxygen - needed for cellular respiration
• -light - some seeds need light
• -temperature - within a certain range
• -extreme conditions - pass through digestive
  system of animal

20
Corn (monocot)

• Appearance of radicle
• Shoot begins to grow
• -cotyledon remains underground

21
Bean (dicot)

1. Appearance of radicle
2. Hypocotyl curves and becomes hook-shaped
3. Hypocotyl straightens after it breaks through the
   soil
4. Embryonic leaves unfold (cotyledons shrink and
   fall off)

22
Asexual Reproduction

• Production of individual without union of gametes
• -clones
• -vegetative reproduction (leaves, stems, roots)
  - table 30-2 p. 623

23
Propagation by humans

• Cuttings
• -roots form from a piece of stem, or shoots form
  on a piece of root (houseplants, ornamental trees
  and shrubs, some fruit crops)
• Layering
• -roots form on stems where they make contact
  with the soil (raspberries)

24

• Grafting
• -joining of two or more plant parts to form a
  single plant
• -bud or small stem of one plant is attached to
  the roots or stem of a second plant (vascular
  cambiums must be aligned)
• -commercial fruit and nut trees, many ornamental
  trees and shrubs

25

• Tissue culture
• -production of new plants from pieces of tissue
  placed on a sterile nutrient medium
• -commercial production of orchids, houseplants,
  cut flowers, fruit plants, and ornamental trees,
  shrubs, and nonwoody plants