Minisymposium 12: Photosynthetic Carbon Metabolism

Add this abstract to my Itinerary

Abs # M1204: The Regulation of Ribulose-1,5-bisphosphate Carboxylase Activity in Response to Variation in Temperature and Atmospheric CO2 Partial Pressure in C3 plants.

Presenter:	Sage, Rowan F       Contact Presenter
Authors	Sage, Rowan F (A)   Kubien, David  (B)   Cen, Yen Peng  (C)
Affiliations:	(A): University of Toronto- Ecology and Evolutionary Biology (B): University of New Brunswick - Biology (C): Queens Univerity - Biology

We measured the temperature response of the net CO2 assimilation rate (A), the rate of whole-chain electron transport, and the activity and activation state of RuBP carboxylase/oxygenase (Rubisco) in sweet potato (Ipomoea batatas), and transgenic tobacco with differing levels of Rubisco. Above the thermal optimum of photosynthesis, the activation state of Rubisco declined with increasing temperature in sweet potato and the wild type tobacco. In sweet potato, doubling CO2 above 370 ppm further reduced the activation state, while reducing CO2 by half increased it. The in vitro rate of electron transport in sweet potato showed a pronounced temperature response with the same temperature optimum as A at elevated CO2. In transgenic tobacco with a third the amount of Rubisco as the wild-type, no reduction in the activation state of Rubisco was observed at elevated temperature, even at elevated CO2. Photosynthesis, by contrast, showed a pronounced reduction above 40C that could be explained by modelled predictions of A parameterized with measured responses of the rate of electron transport to elevated temperature. These results are consistent with the hypothesis that the reduction in the activation state of Rubisco at elevated temperature is largely a regulated response to a limitation in the rate of RuBP regeneration. We were able identify conditions where the deactivation of Rubisco directly limited Rubisco. Measured responses of A to intercellular CO2 indicated the activation state of Rubisco directly limits A at low CO2, 2% O2 and 42C, but not at low CO2, 42C and 21% O2.