plant reproduction

chapter 40

• Alternation of Generations

Haploid (n)

Diploid (2n)

MEIOSISSpore

dispersal

Sporangium

SporangiumMature

sporophyte(2n)

Sorus

Fiddlehead

Spore(n)

Younggametophyte

Maturegametophyte

(n)Archegonium

Egg

Antheridium

Sperm

FERTILIZATION

Newsporophyte

Gametophyte

Zygote(2n)

• Alternation of Generations• Sporophyte - diploid (2n) --> meiosis --> haploid spores• Gametophyte - haploid (n) --> mitosis --> haploid gametes

• fertilization restores diploid

• angiosperms• sporophyte larger and nutritionally independent

• produces spores by meiosis.• gametophyte gives rise to gametes by

mitosis.• pollen grain is the male gametophyte

• Sexual Reproduction? - the flower• produce gametophytes, attract gametophytes, and develop

seeds.• most plants reproduce sexually all reproduce asexually.

FERTILIZATION

Mitosis: division of the nucleus resulting in an exact copy of the

originalMeiosis: reduction in the number of

chromosomes.Gametogenesis: Formation of

sperm and eggs.Fertilization: fusion of sperm and

egg.

flowers• floral anatomy

• arranged in whorls or circles of structures:• Sepals, petals,

stamens, and carpels.

• receptacle• calyx • corolla Sepal

Petal

Receptacle

calyx

corolla

flowers• stamens

• filament and an anther• Each pollen grain

contains two cells; • germinative• vegetative

Stamen Anther

Filament

Microsporangium(pollen sac)

Microsporocyte (2n)

4 microspores (n)

Each of 4microspores (n)

Malegametophyte

Generativecell (n)

MEIOSIS

Ragweedpollengrain

Nucleus oftube cell (n)

MITOSIS

20 µm

75 µm

pollen• pollen production

• each diploid cell produces 4 microspores.

• 4 microspores divide mitotically to form 4 pollen grains • generative cell - sperm nuclei• vegetative cell - pollen tube

• surrounding pollen grain • outer layer - sporopollenin• inner layer - pectin surround

flowers• carpels (pistils) -

• style and stigma• ovary

• contains 1+ ovules.• ovule produces/contains

embryo sac.• embryo sac -

• 2 polar nuclei and 1 egg.

Stigma Carpel

Style

Ovary

Receptacle

Ovule

Megasporangium (2n)

Megasporocyte (2n)

Integuments (2n)

Micropyle

MEIOSIS

Survivingmegaspore (n)

3 antipodal cells (n)

2 polar nuclei (n)

1 egg (n)

2 synergids (n)

Female

gametophyte

Ovule

Embryosac

Integuments (2n)

MITOSIS

100

µm

embryo sac• Producing the female

gametophyte.• ovule

• inner tissue = nucellus • 1-2 protective layers =

integuments• 1 diploid cell in nucellus produces

4 haploid cells• polar nuclei - 2 nuclei remain in

the center of the large cell • mature structure

• female gametophyte or megagametophyte or embryo sac.

floral structure• Variations

• Arrangement of floral parts: spiral or whorled.

• Floral whorls:• Complete

• carpels and stamens:• Perfect• Imperfect

• carpellate or staminate• Sex of the plants:

• Hermaphroditic• monoecious• dioecious

• "Oikos" = house

Stigma

Pollen tube

2 sperm

Style

Ovary

Ovule

Micropyle

Ovule

Polar nuclei

Egg

Synergid

2 sperm

Endospermnucleus (3n)

(2 polar nucleiplus sperm)

Zygote (2n)(egg plus sperm)

Egg

Pollen grain

Polar nuclei

fertilization• fertilization

• Some can self-fertilize• Other cannot self-fertilize -- self-

incompatible• Fertilization

• pollen tube• generative cell divides to form

2 sperm nuclei• endosperm• ovule --> seed• ovary --> fruit

seed development• Endosperm

• 3N nucleus • mitosis

• large multinucleate cell.• cells develop cell wall

• endosperm becomes solid.• mature embryo

• cotyledons • radicle• hypocotyl• epicotyl• plumules

Epicotyl

Hypocotyl

Cotyledons

Radicle

Seed coat

Seed coat

Endosperm

(a) Common garden bean, a eudicot with thick cotyledons

Cotyledons

Epicotyl

Hypocotyl

Radicle

(b) Castor bean, a eudicot with thin cotyledons

(c) Maize, a monocot

Scutellum(cotyledon)

Pericarp fusedwith seed coat

EndospermEpicotyl

Hypocotyl

Coleoptile

RadicleColeorhiza

• Fruits • e.g. apples, oranges,, peaches,

watermelon, cucumber, tomato, peppers

• aggregate fruits • made up of multiple ovaries

• multiple fruits • made up of more than one

flower

• Seed dispersal -- • reduced competition between offspring for resources• decreased relatedness to potential mates• reduced competition between parent and offspring

• agents of seed dispersal --• could eat the fruit (fish, mammals, birds, etc...)• seeds may be transported long distances after being ingested. • seeds may hitch a ride on an organism

pollination• pollination

• coevolution - animal pollinators

• many flowers are wind pollinated

• Asexual reproduction• vegetative reproduction

• no fusion of gametes.• Stems, leaves and roots.

• Apomixis - like parthenogenesis • fragmentation - stems, leaves• Roots can produce aerial shoots