PLANT REPRODUCTION CONCEPTS- Seed Production 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 mechanism Woody 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 gasses Common in hard seed coat types like alfalfa, clovers, as well as some tree species Seed coats may be softened by: Scarification, mechanical abrasion Heat treatment brief exposure to boiling water Acid scarification

The Seed Coat in a dicotyledon Embryo The Seed Coat in a dicotyledon

Seed Dormancy Seed Coat Dormancy Seed coats surrounding embryo may be impermeable to water and gasses Common in hard seed coat types like alfalfa, clovers, as well as some tree species Seed coats may be softened by: Scarification, mechanical abrasion Heat treatment brief exposure to boiling water Acid scarification

Seed Dormancy Embryo dormancy Double dormancy Common in woody perennials (black walnut) Results from physiological or metabolic blocks that need to be removed Stratification exposed to chilling conditions and moist soils, will germinate in spring Double dormancy Seed coat and embryo dormancy in same species

Seed Dormancy Rudimentary embryos Chemical inhibitors Fruits (seeds) discarded or shed before they are mature Needs weeks or months to mature and germinate Chemical inhibitors Inhibitors may be found in endosperm that prevent or delay germination Often 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