UNIT THREE

PLANT REPRODUCTION CONCEPTS- Seed Production

So far in Unit 3 we have talked about plant cell structure and Mendelian genetics. In this lecture we will take a break from Mendel and look at the plant seed. The seed will carry genetic information from one generation to the Next…..so it is worthy of this brief detour

Plant Reproduction Concepts

Seed Dormancy

Seed Germination

Seed Dormancy

“The resting state or quiescence period that occurs in many plant species…but causes are not always the same”

May be a survival mechanismWoody perennials in autumn (apples)

Allows embryonic plant to overwinter in seed form or some form of cold reistance

Seed Dormancy

Seed Coat Dormancy (Go to next slide)Seed coats surrounding embryo may be

impermeable to water and gassesCommon in hard seed coat types like alfalfa,

clovers, as well as some tree speciesSeed coats may be softened by:

Scarification, mechanical abrasionHeat treatment

brief exposure to boiling waterAcid scarification

The Seed Coat in a dicotyledon

Embryo

Seed Dormancy

Seed Coat DormancySeed coats surrounding embryo may be

impermeable to water and gassesCommon in hard seed coat types like alfalfa,

clovers, as well as some tree speciesSeed coats may be softened by:

Scarification, mechanical abrasionHeat treatment

brief exposure to boiling waterAcid scarification

Seed Dormancy

Embryo dormancyCommon in woody perennials (black walnut)Results from physiological or metabolic blocks that

need to be removedStratification

exposed to chilling conditions and moist soils, will germinate in spring

Double dormancySeed coat and embryo dormancy in same species

Seed Dormancy

Rudimentary embryosFruits (seeds) discarded or shed before they are

matureNeeds weeks or months to mature and

germinate

Chemical inhibitors Inhibitors may be found in endosperm that

prevent or delay germinationOften leaching of seeds or exposure to rain will

remove chemical inhibitors

Seed Germination

Sequence of events in seed germination:

Imbibition of water activation of hormones, enzymes embryo growth root and shoot differentiation(seedling establishment)

Bean plant on left showing epigeal germination; corn plant on right showing hypogeal germination ( Do you know the difference?)

Germination Requirements

Adequate moisture

Proper temperature

Good aeration

Light (in some species)

Freedom from pathogenic organisms

Freedom from toxic salts

“The End of a Perfect Day in Plant Science”by Kinkade