FRST 210 lecture 14- SExual reproduction II

Where does the megasporangia and microsporangia arise in the flower?

• Megasporangia=ovary

• Microsporangia=Anther

Meiosis and pollen development in angiosperms

• Inside each microsporangium (pollen sac) within an anther, there are many microspore mother cells

Tapetum

• Nutritive tissue that nourishes the developing microgametophytes

How many microspores does one microspore mother create?

• Microspore via mitosis

• Each microspore develops into a microgametophyte (pollen grain)

• Mitosis creates a generative cell and tube cell (vegetative cell) within the pollen grain

How many celled pollen grains are in a mature microgametophyte?

2

What does the pistil include?

• Stigma, style, and ovary

• The ovary bears ovules (whichcontain a megasporangium and eventually the megagametophyte)

How many ovules does a single megaspore mother cell within an megasporangium (embryo sac) have?

• One, this cell undergoes meiosis!

How does megagametophyte development in angiosperms work?

• A megaspore mother produces forur megaspores via meiosis

  → Only one megaspore develops into a megagametophyte

Second step of megagametophyte development in angiosperms:

• The functional megaspore divides (three times) via mitosis creating 8 nuclei

• Each nucleus is moved to a particular position to form the cells of the megagametophyte

Third step of megagametophyte development in angiosperms:

• Near the micropyle, one nucleus becomes the egg( and two become synergids)

• The opposite end forms three antipodal cells

• The central cell has two “polar nuclei” (→ Cell is diploid)

These processes create a 7-celled (8n nuclei) megagametophyte

Advantages of animal pollination

• Will happen frequently if species are healthy, animals often come back to flowers and carry and disperse pollen around them

• Animals can dleiver pollen more directly to the stigma of a flower

• Animal pollination can facilitate cross-pollination between differen t plants, allowing better genetic diversity

Disadvantages of animal pollination

• In times where animal species may be endangered less flowers are likely to be pollinated, so dependence on pollinators is not perfect

• Changes in resource availability, habitat, and climate can disrupt pollinator-plant interactions, leading to reduced pollination success

• How does the microgametophyte fertilize the macrogametophyte?

• Generative cell divides to create two sperm in microgametophyte→: only one sperm will fertilize the egg to create a zygote (2n)

• The other sperm fuses with polar nuclei to create a triploid cell (3n)

• This process is called double fertilization, creating a zygote

Endosperm

• Triploid, nutritive tissue created from double fertilization as the other sperm fused with polar nuclei

Fruits

• Seeds develop inside ovaries, and ovaries ripen into fruit (protection to seeds)

What are the ploidy for developing seeds? For endosperm?

• Developing seeds have a diploid embryo, with triploid endosperm as nutritive tissue

T/F species develop either pollen or ovules in each flower

T

T/F Do many species produce both micro and megagametophytes (pollen and ovules) within the same flower?

• True, this is called homospory.