SEED AND FRUIT DEVELOPMENT

Seeds:

• Include embryo from fertilized ovum (axis plus

cotyledons), accessory tissues, seed coat

• Accessory tissues: endosperm from fertilized polar

nuclei; sometimes some nucellus ("perisperm", from

megasporangium)

• Seed coat: from integuments

• Cotyledons, endosperm, perisperm store food for

germination: lipid, starch, protein

Seed development:

• Cytokinins in endosperm stimulate cell division of the

fertilized egg

• Auxins produced by embryos stimulate expansion of

cells

Stages of development of an embryo in an Arabidopsis (mouse-ear cress) seed

cotyledon

heart

globular

Courtesy of Prof. John Harada, UCD

In a bean (Phaseolus) seed, the major nutritive tissue is the cotyledon.There is no endosperm remaining

In a grass (Setaria) seed, the majornutritive tissue is endosperm

The castor bean(Ricinus) seedhas both endospermand cotyledon

Fruits: developed ovaries

• Before fertilization, carpel wall (ovary) protects the

ovule and embryo sac and guides the pollen

tube

• After fertilization, the carpel wall changes function

to aid in seed dispersal (and sometimes to

help time germination of the seed)

• Cytokinins in endosperm stimulate cell division

• Auxins produced by embryos stimulate expansion

of cells

• Ethylene stimulates ripening (maturation) of ovary

wall to produce fruit

Types of fruits

--fleshy or dry

--dehiscent (opens to release seeds) or indehiscent

--simple (from one ovary), aggregate (from several

ovaries on one flower), multiple (from inflorescence)

Types of fruits

--fleshy or dry

--dehiscent (opens to release seeds) or indehiscent

--simple (from one ovary), aggregate (from several

ovaries on one flower), multiple (from inflorescence)

Types of fruits

--fleshy or dry

--dehiscent (opens to release seeds) or indehiscent

--simple (from one ovary), aggregate (from several

ovaries on one flower), multiple (from inflorescence)

A pea pod is a dry, dehiscent, simple fruit

A cucumber berry is a fleshy,indehiscent, simple fruit

A strawberry is an aggregate fruit--thetiny individual fruits, achenes, are dry,indehiscent, simple fruits. Thefleshy receptacle develops from the stem

The dandelion head might be considered a multiple fruit. TheIndividual parts are dry,Indehiscent, simple fruits

Why fruits?

They promote dispersal of seed by…

Wind: Winged (ash, elm) and plumed (dandelion)

Water: air-filled (sedges), fibrous (coconut)

Animals: burred, barbed fruits (star thistle, cockelbur); fleshy berries (tomato: the seeds pass through guts); nuts (hidden by squirrels, birds); sticky fruits (mistletoe)

Ulmus

elm

star-thistle

Seed germination

Needs correct conditions (varies by species)

• Temperature (warm enough)

• Temperature history (chilling: “stratification”—

common in high latitudes, unlikely in Vietnam)

• Seed coat breaching (“scarification”)

• Acid bath (animal stomach)

• Light (red or far-red)

• Water (leaches inhibitor [ABA], or simply for turgor

pressure)

Seed germination involves the “mobilization” of storage compounds:their conversion to compounds that can be metabolized for energy and growth

Example: barley seed germination

Summary

•Seeds are plant embryos surrounded by dry integument tissue

•The embryos are dormant when the seeds are mature

•The seed tissues often control germination of the embryonic plant

•Seed tissues--cotyledons, endosperm, perisperm--nourish theseedling when it germinates

•A simple fruit is a mature ovary; aggregate and multiple fruits represent many ovaries

•Fruits promote the dispersal of seeds by wind, water, or animal transport

•Seed germination involves the mobilization of stored compounds