1. Seed development, arrest and germination Seed –Embryo –Seed coat Thick walled cells, waxy –Nutritive tissue Endospermic vs. non-endospermic

2. Seed development, arrest and germination Multiple hormone controls (Fig. 16.10) GA and IAA correlated with rapid cell division and differentiation ABA promotes arrest and dormancy –Via dehydration & inactivates many receptors At maturation arrest occurs– embryo inactive and seed dehydrated

3. Seed development, arrest and germination Germination = > 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

4. GA promotes germination In corn and other grasses, 5. GA also promotes also lipase and protease production IAA stimulates seedling growth

5. Rest vs. dormancy Rest = germinates w/ water, warmth (25-45 o C) and O 2 Dormancy = seeds req’ more developmental signals –Maturation of embryo req’d =After-ripening –Seed coat impermeable to water and O 2 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