Rfr prevents germination rfrr stimulates germination

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Unformatted text preview: ion. R+FR: prevents germination. R+FR+R: stimulates germination. Phytochrome & Phototropism Photoreceptor present in plant tissues: Photoreceptor Phytochrome Phytochrome Occurs in 2 forms: P r & Pfr Synthesized from amino acid precursors as P r. Red light converts it to P (biologically active form). fr Far-red light or periods of darkness cause it to revert to P . r High P inhibits flowering in short-day plants, stimulates it in fr long day plants. long Phytochrome-Mediated Plant Responses Stimulation germination Stimulation in certain seeds. Detection of shading. End of etiolated growth End pattern when seedling emerges into light. emerges Timing of flowering. Dormancy: Arrested Growth (p. 675) (p. Enables survival of unfavorable Enables seasons. seasons. How do seeds/ dormant plants How recognize that it’s spring again? recognize Dormant buds, embryos activated by Dormant specific environmental cues: specific Required cold period Required (stratification): many temperate zone plants. zone Water required to leach inhibitory Water factors from seed coat: Certain desert plants. desert Mechanical abrasion of seed coat Mechanical (scarification): Typical of seeds dispersed by fruit-ingesting animals. animals. Springtime: Carya ovata (shagbark hickory) emerges from dormancy. Dormancy in Buds Dormancy Bud: dormant embryonic shoot/ apical meristem. Structure: • Apical mersitem • Nodes & non-extended internodes • Leaf primordia • Bud primordia • Enclosing bud scales: modified protective Enclosing A hickory bud leaves leaves breaks dormancy Growth inhibitors accumulate in bud scales & Growth other tissues. other Decreasing daylength: important factor inducing Decreasing...
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