Seed development, arrest and germinationSeed

– Embryo– Seed coat

• Thick walled cells, waxy

– Nutritive tissue• Endospermic vs. non-endospermic

Seed development, arrest and germinationMultiple hormone controls (Fig. 16.10)GA and IAA correlated with rapid cell division and differentiationABA promotes arrest and dormancy

– Via dehydration & inactivates many receptorsAt maturation arrest occurs– embryo inactive and seed dehydrated

Seed development, arrest and germinationGermination =

> imbibition of water

> resumption of metabolism

- hydrolitic enzymes mobilize ‘food’ reserves

- Carbohydrate respired &/or gluconeogenesis of fats - resumption of embryo expansion

> seed coat ruptures – radicle (first root) emerges

Seeds time germination w/ sensors

E.g. cryptochrome, phytochrome

GA promotes germination

In corn and other grasses,

5. GA also promotes also lipase and protease production

IAA stimulates seedling growth

Rest vs. dormancyRest = germinates w/ water, warmth (25-45o C) and O2

Dormancy = seeds req’ more developmental signals

– Maturation of embryo req’d =After-ripening

– Seed coat impermeable to water and O2

• Scarification req’d

– Leaching of inhibitors such as ABA, phenolics, coumarin, etc.– E.g. many desert annuals

– Chilling• Stratification req’d

– Light• Sensor is phytochrome