Class Notes (839,471)
Canada (511,354)
Biology (6,826)
Lecture 4


5 Pages

Course Code
Biology 4608G
Norman Huner

This preview shows pages 1 and half of page 2. Sign up to view the full 5 pages of the document.
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
More Less
Unlock Document

Only pages 1 and half of page 2 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.