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18 Cards in this Set
- Front
- Back
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Seeds are dormant structures
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initial embryonic development and endosperm/cotelydon development occur before a seed matures
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Once a seed matures
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-development is arrested
-metabolic rate drops to minimum -water content drops -protects seed from bacteria and funal colonization -seed becomes dormant |
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Germination
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process by which dormant seed resumes normal growth and metabolism
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Breaking dormancy
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dormancy can be mediated externally or internally
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External Mediation-Seed Coat Dormany
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-water is required to break down dormancy
-in many species, the seed coat is impervious to water -scarification |
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scarification
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wounding the seed coat so water can enter and break dormancy
-2 methods, mechanical, and acidic |
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Internal Mediation-After-ripening
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-seed matures before embryo is fully developed
-embryo must finish development before germination is possible |
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Stratification-Temperature Exposure
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-period at some minimum temperature
-blubs, tulips -freez/thaw cycle -heat |
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Germination phase one- Imbibition
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A. Uptake of water prior to an during resumption of growth.
B. Dicots use micropyle |
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Germination phase 2- Emergence
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A. Appearance of roots, shoots, leaves, especially shoots and leaves about soil
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Germination phase 3-Establishment
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A. Onset of photosynthesis in the first true leaves
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Dicot Germination-Epigenous emergence
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-Hypocotyl elongates to form"the hook" which breaks the soil surface, hypocotyl staightens, pulls seed(cotyledon's) above soil.
-Cotyledons protect the epicotyl and plumule as they emerge -Epicotyl elongates, produces first true leaves from plumule |
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Dicot Emergence- Hypogenous Emergence
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-Seed stays below ground
-Epicotyl elongates to form the hook -Drags folded plumule to surface -Plumule forms first true leaves -Cotelydons stay below ground |
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Epigenous and hypogenous emergence
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the radicle emerges first to anchor the plant
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Epigenous Emergence
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Hypocotyl elongates (gets longer) has inverse relationship with Hypogenous
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Hypogenous Emergence
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Epicotyl elongates (gets longer) has inverse relationship with Epigenous
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Monocot Emergence- Hypogenous Emergence
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Plant Example-corn
1. radicle emerges behind coleorhiza to form primary root 2. Mesocotyl elongates and the plumule emerges from soil protected by coleptile 3. plumule forms first true leaves -NO HOOK |
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Monocot Emergence- Epigenous Emergence
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Plant Example-onion
1. Radicle emerges first to form the primary root 2. Cotyledon elongates to form the hook, break the soil, and pulls the endosperm above the soil 3. Cotyledon cracks to allow the plumule to emerge and form the first true leaf |
