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Published on October 16, 2009; 10.1104/pp.109.146514

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Received August 21, 2009
Accepted October 14, 2009

Effect of Rubisco activase deficiency on the temperature response of CO2 assimilation rate and Rubisco activation state: Insights from transgenic tobacco with reduced amounts of Rubisco activase

Wataru Yamori * and Susanne von Caemmerer

Molecular Plant Physiology Group, Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia

* Corresponding author; email: wataru.yamori{at}anu.edu.au.

The activation of Rubisco in vivo requires the presence of the regulatory protein Rubisco activase. To elucidate its role in maintaining CO2 assimilation rate at high temperature, we examined the temperature response of CO2 assimilation rate at 380 μL L-1 CO2 concentration (A380) and Rubisco activation state in wild type and transgenic tobacco with reduced Rubisco activase content grown at either 20°C or 30°C. Analyses of gas-exchange and chlorophyll fluorescence showed that in wild type A380 was limited by RuBP regeneration at lower temperatures, whereas at higher temperatures, by RuBP carboxylation irrespective of growth temperatures. Growth temperature induced modest differences on Rubisco activation state which declined with measuring temperature from mean values of 76% at 15°C to 63% at 40 °C in wild type plants. At measuring temperatures of 25°C and below, an 80% reduction in Rubisco activase content was required before Rubisco activation state was decreased. Above 35°C Rubisco activation state decreased slightly with more modest decreases in Rubisco activase content, but the extent of the reductions in Rubisco activation state were small such that a 55% reduction in Rubisco activase content did not alter the temperature sensitivity of Rubisco activation and had no effect on in vivo catalytic turnover rates of Rubisco. There was a strong correlation between Rubisco activase content and Rubisco activation state once Rubisco activase content was less that 20% of wild type at all measuring temperatures. We conclude that reduction in Rubisco activase content does not lead to an increase in the temperature sensitivity of Rubisco activation state in tobacco.






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