Seed Germination 6v4n6m

Seeds and Seed Germination

© P Billiet

© 2016 Paul Billiet ODWS

Seed structure

Cotyledon Plumule Seed coat or testa

Radicle

Micropyle

© 2016 Paul Billiet ODWS

Seed maturation • Takes place in the fruit on the parent plant • The seeds become dormant • Metabolism falls

• Number of organelles per cell falls • Dehydration

Vacuoles in cells deflate Food reserves become dense crystalline bodies.

© 2016 Paul Billiet ODWS

Maintaining dormancy • Physical barriers

The seed coat (testa) is waxy = waterproof and impermeable to oxygen • Physical state – dehydrated • Chemical inhibitors present e.g. salts, mustard oils, organic acids, alkaloids • Growth promoters absent.

© 2016 Paul Billiet ODWS

Seed viability • Viability: When a seed is capable of germinating

after all the necessary environmental conditions are met • Average life span of a seed 10 to 15 years • Conditions are very important for longevity Cold, dry, anaerobic conditions • These are the conditions which are maintained in seed banks.

© 2016 Paul Billiet ODWS

Germination: The breaking of dormancy The growth of the embryo and its penetration of the seed coat Break down of barriers Abrasion of seed coat Decomposition of seed coat Cracking of seed coat (fire) Change in physical state rehydration

Destruction and dilution of inhibitors Light, temperature, water © 2016 Paul Billiet ODWS

Production of growth promoters

Stages leading to cell division Mitchondria reconstituted

Respiration Initially anaerobic Later aerobic

Soluble sugars

ATP RNA activated Polysomes Protein synthesis (0.5h)

Enzymes (proteins) DNA synthesis (45h) www.rbgsyd.nsw.gov.au/__data/assets/image/81026/

Mitosis (70h)

Factors affecting germination • Water

Rehydration of tissues Dilution of inhibitors • Oxygen (c.f. Respirometer) Aerobic respiration • Warmth Enzyme controlled processes • Some seeds may require exposure to light or high temperatures (fire). © 2016 Paul Billiet ODWS