Seed development arrest and germination Seed Embryo Seed
Seed development, arrest and germination Seed – Embryo – Seed coat • Thick walled cells, waxy – Nutritive tissue • Endospermic vs. non-endospermic
Seed development, arrest and germination Multiple hormone controls (Fig. 16. 10) CK, GA & 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
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
GA promotes germination In corn and other grasses, 5. GA also promotes also lipase and protease production IAA stimulates seedling growth
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, CK impt – Light • Sensor is phytochrome
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