Lecture 9 - Alt. of generations, early plant development

Angiosperms

Group of flowering plants

Angiosperms are…?

The largest phylum of photosynthetic plants

How many species are in the angiosperm phylum?

~300,000

Angiosperm size diversity

1mm - 100 meters

Angiosperm form diversity

Trees, bushes, grasses, vines, cacti, aquatic

What percent of all plant species includes Angiosperms?

~75-80%

Largest angiosperm

Eucalyptus!

Smallest angiosperm

Duckweed

Characters of Angiosperms

• Flower production

• Double fertilization

• Seeds produced in enclosed ovary, which is fruit

Flower

Determinate shoot of the sporophyte, bears modified leaves for reproduction

Angiosperms include

• all hardwood trees

• herbaceous and woody plants

Cotyledon

Embryonic leaves that provide nutrients for seedlings before true leaves begin photosynthesizing

Monocots #

One cotyledon

Eudicot #

Two cotyledons

Monocots include…

Corn, wheat, lillies, orchids and palms

Eudicots include…

Roses, clover, tomatoes, oaks, and daisies

Monocot leaf venation

parallel

Eudicot leaf venation

netlike

Monocot stem

Complex vascular bundle organization

Eudicot

Vascular bundles in rings

Monocot root system

fibrous

Eudicot root system

Taproot

Monocot flower #

multiples of three

Eudicot flower #

multiples of four or five

Alternation of generations photo

Alternation of generation cycle

• gametophyte plant produces sperm and eggs

• 1n sperm and egg fuse to form 2n zygote

• zygote begins sporophyte/diploid generation

Where does reproduction take place in angiosperms?

The flower

Male gametophyte

develops within anther, spore cells undergo meiosis, which produces haploid pollen grains

Female gametophyte

develops in ovules

• embryo sac = female gametophyte

• contains eight nuclei that divide into eggs

Microsporogenesis

formation of microspores within the microsporangia/pollen sacs

microsporocytes

• in anther

• divide via meiosis to product 4 microspores

microgametogenesis

development of male gametophyte/microspores into pollen grains/microgametophytes

mature pollen grain cell types

tube, generative

megasporogenesis

formation of megaspores within the megasporangium

megasporogenesis process

• one megasporocyte develops and divides by meiosis

• three of four haploid megaspores die, leaving one megaspore

megagametogenesis

megaspore divides 3 times by mitosis to form 8 nuclei

arranges into female megagametophyte

double fertilization yields

zygote and endosperm

zygote ploidy

2n

formed by unity of sperm nucleus and egg

endosperm ploidy

3n

provides nutrients to developing embryo

endosperm development

• triploid nucleus divides many times

• supercell undergoes cytokinesis to form cell mem/walls, becomes multicellular

Endosperm purpose

provides nutrients to developing embryo

Monocot endosperm

stores nutrients for use after germination

Eudicot endosperm

reserves of endosperm are exported to cotyledons

Embryo development

• grows with mitotic divisions

• cotyledons appear

• basic body plan appears

• apical meristems produced

• seed produced

Suspensor

extension at the base of embryo that anchors it in the embryo sac

aids in nutrient/hormone transfer between embryo and parent

embryo development multistep process

• established polarity

• designating tissue layers

• determining body plan

cotyledon

embryonic leaf, nutrient storage and absorption

hypocotyl

part of embryo between leaves and radicle

radicle

embryonic root

label embryonic plant

unique feature of monocot development

• scutellum

• coleoptile

• coleorhiza

scutellum

Specialized cotyledon w/ large surface area to absorb nutrients from endosperm during germination

coleoptile

Sheath that protects shoot

coleorhiza

Protects root

label monocot embryo