Plant Reproduction

Goals

1. To become familiar with the life cycle of flowering plants

2. To understand how plant life cycles differ from those of animals

3. To understand the strategies that plants use in manipulating animals to disperse their pollen and seeds

Outline

Asexual reproduction

Cloning by fragmentation -- stolons, suckers, bulbs, etc.

Cloning with seed production -- apomixis

Sexual reproduction: Animal life cycles vs. plant life cycles

Animal life cycles:

gametes formed by meiosis, no haploid mitosis

Plant life cycles: alternation of generations

spores formed by meiosis, haploid mitosis, gametes formed by mitosis

The Angiosperm life cycle

Flower morphology

Receptacle

Non-sexual parts:

Sepals -- enclose and protect floral bud

Petals -- attract pollinators

Sexual parts: carpel (female) and stamens (male)

Stamens = filament + anther

Carpel = ovary (containing ovule[s]) + style + stigma

Formation of the gametophyte (meiosis, then mitosis)

male: occurs in anthers, in pollen sac

meiosis produces a microspore (n), which produces a generative cell and a tube cell

pollen = male gametophyte (2 haploid cells)

female occurs in ovule, in embryo sac

meiosis produces one functional megaspore (n), which produces an egg cell + 2 polar nuclei + 5 other cells

= female gametophyte (8 haploid cell nuclei)

Pollination and double fertilization

Pollination = transfer of pollen from anther to stigma (by wind, insects, birds, etc.)

Pollen grain germinates, sends pollen tube down stigma to ovule. Generative cell nucleus undergoes mitosis and the resultant sperm nuclei travel down tube.

Sperm nuclei fertilize egg (Æ zygote [2n]) and polar nuclei (Æ endosperm nucleus [3n])

Formation of seed and fruit

Seed:

Zygote undergoes mitosis, and develops into embryo

Endosperm nucleus and cytoplasm divide and give rise to endosperm; function = food for embryo

Ovule wall becomes seed coat (parental tissue); function = seed protection

Ovary wall becomes fruit (also parental tissue); function = seed dispersal (or protection)

Embryo = cotyledon(s) + embryonic root and shoot systems

Dicots: two cotyledons, which have absorbed all of endosperm

Monocots: one cotyledon, typically absorbed after seed germination

Pollination

wind

animals

mutualism -- both species benefit

goals of the plant -- multiple stops at flowers of same species

floral syndromes

Fruits

function: seed dispersal -- may be fleshy or dry

wind

water

animals

seeds may be dispersed internally or externally

seeds may be dispersed voluntarily or involuntarily

 

Vocabulary

click here to go to plant reproduction vocabulary