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Plant bio
Red light
| Question | Answer |
|---|---|
| Skotomorphogenesis (etiolated) | - dark grown (adapted to underground light) Long hypocotyl Incapable of photosynthesis Closed unexpanded cotyledons Apical hook |
| Photomorphogenesis (de-etiolated) | - light grown (adapted to growth in light) Shorter hypocotyl Capable of photosynthesis Expanded cotyledons |
| Effects of red light on germination | - red light stimulates germination, while far red light inhibits |
| Photoreversibility | Red/far red reversibility is a characteristic of processes regulated by phytochromes (‘plant-colour’) |
| Phytochrome-regulated photoreversible responses | Effects of red light Seed - promotes germination Seedling - promotes photomorphogenesis and leaf primordia Adult - inhibits flowering and internode elongation |
| Phytochrome | ~125 kDa protein - exists in two forms: Pr - blue protein (absorbs red light) Pfr - blue-green protein (absorbs far red light) |
| Phytochrome absorbance spectra | In red light, equilibrium: 15% Pr : 85% Pfr In far-red light, equilibrium: 97% Pr : 3% Pfr Both Pr and Pfr also absorb blue and UV-A |
| Pfr - the physiologically active form | Usually, red light induces a response and far-red reverses* Theoretically, this could be due to decrease in Pr or increase in Pfr |
| What is the evidence that Pfr accumulation induces response? | Magnitude of response is proportional to amount of Pfr Arabidopsis mutants: HY1 and HY2 proteins are required for chromophore biosynthesis and hy1 and hy2 mutants lack active phytochrome (incl. Pr). Thus absence of Pr does not induce response |
| Phytochrome structure | Chromophore NH2 - PAS GAF PHY PRD PRD HKRD - COOH |
| Phytochrome structure pt 2 | PRD (PAS-related domain) contains nuclear localisation signals HKRD (histidine kinase-related domain) Plant phytochromes are actually ser/thr protein kinases |
| Phytochromobilin: the phytochrome chromophore | - covalently linked linear tetra-pyrrole - autocatalytic reaction with apoprotein - Structural change in chromophore causes structural change in protein |
| Types of phytochromes | Arabidopsis phytochrome genes: PHYA type I PHYB type II PHYC type II PHYD type II PHYE type II |
| What are VLFR, LFR and HIR? | Phytochrome responses can be distinguished by amount of light required and mediated by different phytochromes VLFR = very low fluence response LFR = low fluence response HIR = high irradiance response |
| Photomorphogenesis mediated by PhyA and PhyB phytochromes | - phyB mutants are compromised in red light induced photomorphogenesis - phyA mutants are compromised in far-red light induced photomorphogenesis |
| How does R and FR light vary? | - massively in different light conditions/environments |
| Shade avoidance | - plants in shade see decrease in Pfr/P total, and less growth |
| Mechanisms of phytochrome action? | - conformational change - photo-sensing domain changes |
| Nuclear localisation | - Arabidopsis phyA-GFP localisation: all dark - Arabidopsis phyB-GFP localisation: spotty flourescent light |
| Alterations of gene expression | Transcription of MYB and LHCB (light harvesting chlorophyll a/b binding protein) genes in Arabidopsis, darkness to white light |
| Direct regulation of gene expression | Regulation of degradation of activators and inhibitors of transcription |
Created by:
reub8n
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