Angiosperm Reproduction and Biotechnology

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In most monocots and some eudicots, endosperm stores nutrients that can be used by the seedling.

In other eudicots, the food reserves of the endosperm are exported to the cotyledons.

Slide 25

Structure of the Mature Seed

The embryo and its food supply are enclosed by a hard, protective seed coat.

The seed enters a state of dormancy.

Slide 26

In some eudicots, such as the common garden bean, the embryo consists of the embryonic axis attached to two thick cotyledons (seed leaves).

Below the cotyledons the embryonic axis is called the hypocotyl and terminates in the radicle (embryonic root); above the cotyledons it is called the epicotyl.

Slide 27

Seed Structure

Epicotyl

Hypocotyl

2 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 fused

with seed coat

Endosperm

Epicotyl

Hypocotyl

Coleoptile

Radicle

Coleorhiza

Slide 28

Epicotyl

Hypocotyl

Cotyledons

Radicle

Seed coat

Common garden bean, a eudicot with 2 thick cotyledons

Slide 29

A monocot embryo has one cotyledon.

Grasses, such as maize and wheat, have a special cotyledon called a scutellum.

Two sheathes enclose the embryo of a grass seed: a coleoptile covering the young shoot and a coleorhiza covering the young root.

Slide 30

Maize = corn , a monocot

Scutellum

(cotyledon)

Pericarp fused

with seed coat

Endosperm

Epicotyl

Hypocotyl

Coleoptile

Radicle

Coleorhiza

Slide 31

Seed Dormancy: An Adaptation for Tough Times

Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling.

The breaking of seed dormancy often requires environmental cues, such as temperature or lighting changes.

Slide 32

Seed Germination and Seedling Development

Germination depends on imbibition, the uptake of water due to low water potential of the dry seed.

The radicle (embryonic root) emerges first.

Next, the shoot tip breaks through the soil surface.