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Lecture 4

LECTURE 4.pdf

5 Pages
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Department
Biology
Course Code
Biology 4608G
Professor
Norman Huner

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Long-term Photoacclimation and Photoadaptation February-08-12 1:33 PM In short-term - photoacclimation - Xanthophyll cycle, state transition - no de novo synthesis Integration of long and short term acclimation processes over time Chlorella vulgaris - doubling time of about a half hour? - See effects of photoacclimation at the level of phenotype- reflects different time scales - stress vs acclimation - Reflected in level of proteins and pigments - Change in phenotype can be accounted for at levels of transcription/translation - Plant must be sending change in light to induce change in phenotype - Sensor is ETC - redox state of the PQ pool Lecture 4 Page 1 - PSII - large antenna, large sigma PSII ○ LHC shrinks in response to light - decrease in sigma PSII, decrease in efficiency with which the organism will use the light  Helps cells survive condition ○ In long-term - light saturated, light not limiting, can decrease efficiency - DCMU binds to the Qb binding site of PSII - where plastoquinone dissociates when reduces by Qa (photochemistry) and protonated using H+ from stroma - DCMU binds - inhibits electron transport - electrons no longer coming out of PSII ○ DCMU is an herbicide ○ PSI is still operating in the light - over oxidation of the PQ pool for at least one life cycle- chlorella will survive - DBMIB - specifically binds and inhibits cytb6f complex - PQ pool would be over reduced ○ Yellow cells ○ Redox state of the PQ pool - over reduced causes yellow phenotype  Modulates the phenotype - Chloroplast must be giving a redox signal that is regulating gene expression ○ Genes are in the nucleus - communication? - Phenotypic change is due to major changes in LHC - builds a much smaller PSII - trimeric LHC units that are being affected (associated with core antenna) Lecture 4 Page 2 - Reduction in number of trimers that are associated with core PSII - smaller sigma PSII - decreases photosynthetic efficiency ○ CO2 assimilated/photon absorbed ○ Takes more photons to fix a mole of CO2 ○ REVERSIBLE - Not all green algae display this response ○ Raudensis - does not show change in phenotype at higher light intensity ○ Growth rate - vulgaris no change with high light intensity  Growth is the ultimate sink - represented by tau-1 ○ Raudensis doubles growth rate at high light - Chlorella is limited whereas UWO241 doesn't change its phenotype ○ Vulgaris - cant adjust the growth rate due to light - increased intensity, energy needs to be dissipated ○ UWO241 can respond to high light by increasing tau-1 - utilizes energy to increase the growth rate - no need to change pigmentation - more light, will grow faster  No change in sigma PSII in response to the irradiance - Both eukaryotic, single cell - one chloroplast per cell Terrestrial plants - Sun plants - able to acclimate - many crop plants ○ Grow both in shade and full sunlight ○ Light response curve - grown under high light and low light - measure response curve  Same plant species  Maximum light saturated rate is a measure of photosynthetic capacity  Change in efficiency and capacity with HL/LL ○ High light - high capacity, reduced efficiency  Reduces sigma PSII to reduce efficiency  Photosynthesis is limited by the turnover of RuBP ○ Light saturating - Calvin cycle is saturated with RuBP - ability of rubisco to utilize RuBP is limiting, cant use fast enough ○ Increase the light saturated rate of photosynthesis by making more rubisco  Higher levels of rubisco - increases light saturated rate of photosynthesis ○ Low light plants - lower levels of rubisco - lower light saturated rate of photosynthesis - Plants are decreasing photosynthetic efficiency - sigma PSII is changing by changing amount of LH polypeptides, can also modulate sigma PSII by modulating xanthophyll cycle ○ Requires gene expression ○ Retrograde regulation of genes  PQ pool is redox sensor conveying some kind of signal to nucleus to regulate expression of nuclear coded genes involved in photosynthesis - Adjustment of sigma PSII occurs due to limitation in photosynthetic capacity (HIGH LIGHT) - because light is not limiting - too much light, wants to absorb less ○ Ultimate sink - growth and development - growth limitation, reduce energy to maintain photostasis Lecture 4 Page 3 - Adjustment of sigma PSII occurs due to limitation in photosynthetic capacity (HIGH LIGHT) - because light is not limiting - too much light, wants to absorb less ○ Ultimate sink - growth and development - growth limitation, reduce energy to maintain photostasis  Growth cannot keep up with high
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