Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2000
Publication Date: N/A
Technical Abstract: The activity of isolated Rubisco increased with temperature at both air- levels and at saturating CO2. In contrast, net photosynthesis (CER) at air- levels of CO2 was inhibited by moderately high temperatures. When the internal CO2 concentration was doubled, CER increased with temperature but only up to 40 deg C. At air-levels of CO2, the activation state of Rubisco oin leaves decreased progressively as temperature increased, with no decrease in RuBP regeneration capacity. An even greater decrease in Rubisco activation occurred when temperature was increased at high CO2. To determine if activase per se was the principle limitation in the system, we measured activation of Rubisco by activase in a reconstituted assay. The results showed that the ability of activase to maintain a high steady-state of Rubisco activation decreased with temperature and could be partially restored by adding higher amounts of activase. In the absence of activase, ,Rubisco deactivated faster and to a greater extent under catalytic conditions as the incubation temperature increased. Taken together, our results indicate that increased catalytic turnover of Rubisco at higher temperatures increased the rate of Rubisco inactivation to a level that exceeded the capacity of activase to maintain a constant activation state. Thus, as temperature increases, the photosynthetic potential of leaves may be limited by Rubisco activase even at high CO2.