1 CBMG688R. ADVANCED PLANT DEVELOPMENT AND PHYSIOLOGY II G. Deitzer Spring 2006 LECTURE Photomorphogenesis and Light Signaling Photoregulation 1. Light Quantity 2. Light Quality 3. Light Duration 4. Light Direction I. Light Quantity Photosynthesis Photoreceptors Chlorophylls Carotenoids Photosynthesis Light Capture II. Light Quality Photosynthetic Efficiency Low Light Grana Stacking Low Red : Far-Red Ratio (high far-red) Phosphatase Remove PO4 LHCII particles bond together High Light Grana Unstacking High Red : Far-Red Ratio (high red) Kinase Form PO4 bonds to LHCII LHCII particles separate Emerson Enhancement Effect Far-Red induced increase in efficiency Photomorphogenesis Seed Germination Release from dormancy Weed seeds Red Light (5 sec) Induce Germination Far-Red (5 sec) Inhibit Germination R + FR - Inhibit R + FR + R - Induce
Seedling Development Etiolated Dark long, spindly, white (or yellow) De-Etiolated Light Red Light ( 5 sec pulse) short, thick, green R + FR etiolated Internode Elongation Shade Adapted (Shade Tolerant) No Response Shade Avoidance (Shade Sensitive) Low Red : Far-Red Ratio Canopy Shade Rapid Elongation Escape Shade Planting Density Nearest Neighbor Detection Reflected Far-Red Light Rapid Elongation Tall Plants - Center of dense plot Less Grain Yield More Vegetative Growth Short Plants - Edges of dense plot Less Dense Plot High Grain Yield Less Vegetative Growth III. Light Duration Photoperiodism Daylength Perception Short-Day Plants Dark Period - Longer than Critical Minimum 5 min Night Break Red - Inhibit Flowering Far-Red - Flowering R + FR + R - No Flowering Long-Day Plants Dark Period - Less than Critical Maximum 2
3 End-Of-Day Far-Red 8 hr day + 5 min R - No Flowering 8 hr day + 5 min FR - Flowering 8 hr day + FR + R - No Flowering Night Break - Not very effective Daylength Extension Low Red : Far-Red Ratio Like Shade Avoidance Promotes Flowering Not R/FR reversible IV. Directional Information Phototropism Blue Light Stem Bending Toward Light Lateral Redistribution of Auxin Auxin High on Shaded Side Increased Growth Stomatal Opening Blue Light Activation of ATPase H+ ion extrusion H2O uptake Leaf Movement Heliotropism - Legumes Pulvinus Similar to Stomatal Opening Multicellular H+ / K+, Cl- exchange ---> H2O uptake ---> Swelling Dorsal <---> Ventral Dorsal swell ---> Leaf moves down Ventral swell ---> Leaf moves up Paraheliotropism parallel to light Soybeans Orthoheliotropism perpendicular to light Sunflower Solar Tracking V. Photoreceptors (Pigments) 1. Photosynthesis Chlorophylls Carotenoids
4 Energy Transfer Light ----> Chemical Energy 2. Photomorphogenesis & Photoperiodism Red / Far-Red Reversible Phytochrome Dark Red Dark P ------->Pr -----660 nm -----------> Pfr ------> Response <----730 nm----------- Far-Red Molecular Switch Pfr - Active Form 5 Phytochromes (Multigene family) phya ------> FR inhibition of Stem elongation etiolated plants phyb ------> R inhibition of Stem elongation etiolated plants -----> FR promotion of internode elongation shade avoidance -----> FR promotion of flowering daylength extension phyc ------>? phyd ------>? EOD FR promotion of flowering? phye ------>? Mechanisms of Action Histidine Kinase Autophosphorylation Nuclear Import Pr - Cytoplasm (Synthesis) Pfr Nucleus (Speckles) Pfr-PIF3 (bhlh Transcription Factor) MYB protein expression (PHYB) 3. Light Direction Phototropism & Heliotropism Blue-Light-Absorbing Photoreceptor (BLAP) Cryptochrome Hypocotyl Elongation, Circadian Clock CRY1 & CRY2 N-Terminal Pterin + FAD Binding Similar to Photolyase but no activity No Kinase activity
Phototropin Hypocotyl Bending, Stomatal Opening PHOT1 & PHOT2 Flavoprotein 2 LOV Domains + 2 FMN N-Terminus ser/thr Kinase activity C-Terminus Carotenoid (Zeaxanthin) 4. UV Absorbing Photoreceptor (None Identified) UV-B DNA Thymidine Dimers Chromosome Damage UV-A Protein Photolyase DNA Repair 5