Angiosperm Reproduction

1
Angiosperm Reproduction

• Chapter 38

2
Review of Angiosperm Life Cycle
3
Review of Flower Structure

• sepals (infertile) enclose protect the floral
  bud
• petals (infertile) attract pollinators
• stamen (fertile) made of a filament (stalk)
  anther (site of pollen production)
• carpel (fertile) consists of a stigma (pollen
  landing site), style, ovary (location of
  ovules)
• all floral organs attached to the stem at the
  receptacle

4
Floral Variations

• complete vs. incomplete flowers
• all 4 basic floral organs present complete
  flower
• 1 or more floral organs absent incomplete
  flower
• flowers can be sterile, female (carpellate), male
  (staminate)
• creates monoecious dioecious plants
• bilateral vs. radial symmetry
• superior, semi-inferior, or inferior ovary
  position
• individual or clustered flower distribution
• clusters are called inflorescences
• other size, shape, color, odor, arrangement of
  floral organs

5
Gametophyte Development
6
Male Gametophyte Pollen Grain

• develop within microsporangia located in anthers
• diploid cells within microsporangia divide by
  meiosis to produce microspores
• microspores develop into pollen grains
• pollen grains become mature gametophytes when the
  generative nucleus divides forms 2 sperm
  (usually occurs post-pollination)

7
Female Gametophyte Embryo Sac

• develop within megasporangia located within
  ovules
• each megasporangium contains 1 large diploid cell
  that divides by meiosis to produce 4 haploid
  cells but only one survives (megaspore)
• the megaspore divides 3 times by mitosis without
  cytokinesis, producing a large cell with 8
  haploid nuclei
• this large cell is partitioned into 7 cells (one
  with 2 nuclei) producing a multicellular female
  gametophyte (embryo sac)

8
Pollination

• transfer of pollen from an anther to a stigma
• when successful, pollen grain produces a pollen
  tube which grows through the style to the ovary
  where it releases two sperm into the embryo sac

9
Preventing Self-Fertilization

• dioecious plants
• floral organs mature at different times
• arrangement of floral organs pin vs. thrum
• self-incompatibility a biochemical block that
  prevents pollen tube growth
• controlled by S-genes
• 2 mechanisms
• S-genes of gametophyte govern blocking
• S-genes of sporophyte govern blocking

S1
S1S2
S2S3
10
Double Fertilization

• one sperm fertilizes the egg to form the zygote
• the other sperm combines with 2 polar nuclei to
  form a triploid (3N) cell that gives rise to the
  endosperm (food-storing tissue of the seed)

11
Seed Formation

• seeds develop from the ovules
• endosperm development
• usually precedes embryo development
• in most monocots many eudicots, the endosperm
  stores nutrients that can be used by the seeding
  after germination
• in other eudicots, the food reserves of the
  endosperm are transferred to the cotyledons
  before the seed completes its development

continued on next slide
12

• embryo development
• 1st division of the zygote produces 2 cells
• terminal cell gives rise to the embryo
• basal cell produces the suspensor which anchors
  the embryo to its parent functions in the
  transfer of nutrients from parent to embryo
• cotyledons develop 1st on the young embryo then
  the embryo lengthens
• the shoot apical meristem develops between the
  cotyledons
• root apical meristem develops where the embryo
  attaches to the suspensor
• seed maturation the seed dehydrates the
  embryo becomes dormant

13
Seed Structure

• seed coat formed from integuments of ovule
• hypocotyl portion of embryo below cotyledons
• epicotyl portion of embryo above cotyledons
• radicle embryonic root

14
Fruit Development

• ovary develops into fruit at the same time seeds
  are developing from ovules
• triggered by hormonal changes following
  fertilization
• ovary wall becomes the pericarp (thickened wall
  of the fruit)
• a fruit usually ripens at about the same time
  that its seeds complete their development

15
Types of Fruits
16
Seed Germination

• breaking dormancy requires certain environmental
  conditions
• ex substantial rainfall, intense heat (fire),
  extended exposure to cold, light, chemical attack
  (from animal digestive tract)
• germination depends on imbibition the uptake of
  water due to the low water potential of the dry
  seed
• causes the seed to expand break its seed coat
• triggers metabolic changes in the embryo that
  enable it to resume its growth

continued on next slide
17

• the radicle is the first organ to emerge from the
  seed
• next, a hook forms in the hypocotyl and growth
  pushes the hypocotyl thru the soil surface, where
  exposure to light causes it to straighten raise
  the cotyledons and epicotyl
• epicotyl then spreads its first foliage leaves
  (true leaves) which expand, become green, begin
  making food by photosynthesis
• cotyledons shrivel fall away

NOTE monocots use a different method for
breaking ground. The sheath that encloses
protects the embryonic shoot (coleoptile) pushes
through the soil, providing a tunnel for the
shoot tip to grow out of.
18
Asexual Reproduction

• a.k.a vegetative reproduction because offspring
  are usually mature, vegetative fragments from the
  parent plant
• natural mechanisms
• fragmentation the separation of a parent plant
  into parts that develop into whole plants
• apomixis asexual reproduction of seeds
• human-generated mechanisms
• cuttings
• grafting
• test-tube cloning (which facilitates genetic
  engineering of transgenic plants)