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Unformatted text preview: ion. R+FR: prevents germination. R+FR+R: stimulates germination. Phytochrome & Phototropism
Photoreceptor present in plant tissues:
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
long day plants.
long Phytochrome-Mediated Plant
Responses Stimulation germination
in certain seeds.
Detection of shading.
End of etiolated growth
pattern when seedling
emerges into light.
Timing of flowering. Dormancy: Arrested Growth (p. 675)
(p. Enables survival of unfavorable
How do seeds/ dormant plants
recognize that it’s spring again?
Dormant buds, embryos activated by
specific environmental cues:
specific Required cold period
(stratification): many temperate
zone Water required to leach inhibitory
factors from seed coat: Certain
desert Mechanical abrasion of seed coat
(scarification): Typical of seeds
dispersed by fruit-ingesting
animals. Springtime: Carya ovata
emerges from dormancy. Dormancy in Buds
Bud: dormant embryonic shoot/ apical meristem.
• Apical mersitem
• Nodes & non-extended internodes
• Leaf primordia
• Bud primordia
• Enclosing bud scales: modified protective
A hickory bud
Growth inhibitors accumulate in bud scales &
Decreasing daylength: important factor inducing
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- Spring '14