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Brassinosteroid mutants show dwarf phenotypes
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Brassinosteroid signal transduction goes through kinases
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Phytochrome – the classical photoreceptor
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Development (realization of a phenotype from a genotype) is controlled by endogenous factors intercellular regulation phytohormones exogenous factors biotic factors abiotic factors
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Photomorphogenesis Skotomorphogenesis (etiolation)
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Light has an influence on seedling development Photomorphogenesis inhibition of hypocotyl elongation opening of apical hook cotyledon expansion chloroplast development DarkLight
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Dark Light wild-type cop/det mutants COP and DET proteins inhibit photomorphogenesis
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Germination of lettuce seeds (photoreversibility) Reversible R/FR response system controlled by phytochrome germination
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Pr Pfr Red light Far-red light inactive active Phytochrome dogma
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synthesis germination, flower Induction…… red light far red light Phytochrome: from synthesis to action
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blue lightred light
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Arabidopsis: 5 phytochrome proteins (phyA - phy E), differ in their apoproteins Phytochrome : homodimeric chromoprotein: apoprotein and phytochromobilin (open chained tetrapyrrol) as chromophor form holoprotein
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Strasburger, 2002 Structure of phytochrome proteins
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Phytochrome responses vary with amount of light VLFR: 0.00001 µmol x m -2 LFR: 1-1000 µmol x m -2 Arabidopsis seed germination Lettuce seed germination Anthocyanin synthesis Inhibition of hypocotyl elong. Enlargement of cotyledons Apical hook opening HIR: >1000 µmol x m -2 x s -1
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Phytochrome responses vary with amount of light Inhibition of hypocotyl elongation HIR: >1000 µmol x m -2 x s -1
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Phytochrome responses vary with amount of light LFR: 1-1000 µmol x m -2 Lettuce seed germination
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Strasburger, 2002 Phytochrome in seedlings
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Strasburger, 2002 Shade avoidance reaction
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Strasburger, 2002 Shade avoidance reaction
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Strasburger, 2002 Shade avoidance reaction
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Strasburger, 2002 Shade avoidance reaction
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Strasburger, 2002 RFR PR inactive PFR active P FR active P R inactive sensor signal transduction Regulatory function
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PHYA-GFP and PHYB-GFP fusion proteins migrate into the nucleus PHYA-GFP PHYB-GFP Dark Red
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Gene activation through phytochrome Nuclear import DNA binding Gene activation
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Pr Pfr Red light Far-red light Photoequilibrium: 660 nm 80% Pfr 730 nm 2-3% Pfr R/FR Sunlight:1.13 Dusk: 0.8/0.9 Shade of leaves:0.2 inactiveACTIVE !!!
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Red light Far-red light Pr Pfr Two holoproteins (+chromophore) form a dimer Histidine kinase related Chromophore binding domain IIA IA IIB IB IA IIA IIBIB
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N-terminal extension Hinge region PAS domain Histidine kinase related 1 Histidine kinase related 2 Chromophore binding domain The Phytochrome apoprotein (-chromophore) is a 125kD monomer Chromophore binding domains Two holoproteins (+chromophore) form a dimer IIA IA IIB IB
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