|Schrader, Stephen - UNIV OF WISCONSIN|
|Wise, Robert - UNIV OF WISCONSIN|
|Sharkey, Thomas - UNIV OF WISCONSIN|
Submitted to: Plant Biology
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2003
Publication Date: August 1, 2003
Citation: Schrader, S., Wise, R., Ort, D.R., Sharkey, T. 2003. Moderate heat stress on photosynthesis: is rubsico activase the problem or the solution [abstract]? Plant Biology. Paper No. 384. Available: http://abstracts.aspb.org/pb2003/public/P37/1300.html. Technical Abstract: Moderately high temperatures reduce photosynthetic CO2 accumulation. Previous research has identified rubisco activase and thylakoid energization as heat labile components of the photosynthetic apparatus. Ribulose 1,5-bisphosphate (RuBP) regeneration is dependent on photophosphorylation, and rapid heating from 30°C to 40°C reduces RuBP levels by 28% while rubisco activation declines only 3%. After heating at 45°C for 5 minutes, RuBP levels recovered and rubisco activation was down 45%. This indicates that RuBP levels drop initially during heating and then recover as rubisco is deactivated. Electron transport rate (etr) after heating for 15 minutes at 42°C also indicated that the limiting component of photosynthesis is the thylakoid membrane. Finally, the electrochromic shift at 518 nm indicated that thylakoid membranes de-energize more rapidly at 36°C while still able to form a highly energized membrane, thus indicating increased thylakoid permeability to protons. This data indicates that the primary problem of heat stress on photosynthesis is with the light reactions. Why then does rubisco deactivate? Rubisco may deactivate to reduce ATP useage by the Calvin Cycle and so maintain a highly energized thylakoid, which may protect the membrane from heat damage.