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Seed development, arrest and germinationSeed
– Embryo– Seed coat
• Thick walled cells, waxy
– Nutritive tissue• Endospermic vs. non-endospermic
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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
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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
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GA promotes germination
In corn and other grasses,
5. GA also promotes also lipase and protease production
IAA stimulates seedling growth
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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