Seed development, arrest and germination

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 (25-45o 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