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Plant bio

Blue light

QuestionAnswer
How do plants react to blue light? Chloroplast movements Sun tracking by leaves Phototropism Photomorphogenesis, including: Inhibition of hypocotyl elongation Stimulation of chlorophyll synthesis - Phytochrome senses presence and quality of light
What is phototropism? - movement of plants towards light
How does phototropism work? light gradient - unequal light perception - unequal auxin - unequal cell elongation - bending - one side shaded, other illuminated
Inhibition of stem elongation - uv-a and blue light: active in inhibiting hypocotyl elongation - yellow light establishes constant pr:pfr light ratio
How long does inhibition take? Phytochrome-mediated inhibition: 8 - 90 min Blue light mediated inhibition: 15 - 30 s
Regulation of gene expression Most light responsive genes respond to red and blue
Stomatal opening Stomatal opening is promoted by: - Photosynthesis (DCMU partially inhibits) - Blue light Experimentally stomatal opening is also inhibited by orthovanadate (an inhibitor of H+-ATPase) and induced by fusicoccin (an activator of H+-ATPase)
How does stomatal opening work? blue light - uptake of ions and synthesis of organic solutes - decreased water potential - influx - swelling - pore opening
Blue light receptors: cryptochromes HY4 = CRY1 Mutants lack blue light dependent inhibition of hypocotyl growth
What biological responses are mediated by cryptochromes? Photomorphogenesis : cotyledon opening, cotyledon size, anthocyanin accumulation, hypocotyl length Flowering time and circadian rhythm Anthocyanin accumulation Phototropism (low fluence only: ‘first positive curvature’)
Cryptochrome signal transduction: how is transcription and protein degredation regulated? CRYs interact with CIB transcription factors, which then interact with the FT gene to promote floral initiation
CRYs interact with SPA proteins to suppress SPA activation of COP1-mediated degradation of HY5, HYH, CO and other regulators of light-regulated gene (LRG) transcription
Blue light photoreceptors: phototropins NPH1 = Phototropin1 (PHOT1) - bend to light and open stomata
Mechanisms of phototropism 1) light - auxins move downward 2) light moves - auxins move to side 3) as more auxins move, plant grows bending
What is Zeaxanthin? - photoreceptor that absorbs blue light
Role of Zeaxanthin in blue light sensing in guard cells Xanthophyll cycle: Zeaxanthin is formed in thylakoids by reversible de-epoxidation of violaxanthin - npq1 mutation results in no zeaxanthanin formed in strong light
Mutant sensitivity - phot1/2 and wildtype react strongly to blue light
Created by: rose.coo
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