Changes in Growth CO(2) Result in Rapid Adjustments of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Small Subunit Gene Expression in Expanding and Mature Leaves of Rice

The accumulation of soluble carbohydrates resulting from growth under elevated CO(2) may potentially signal the repression of gene activity for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcS). To test this hypothesis we grew rice (Oryza sativa L.) under ambient (350 μL L(−1)) and high (700 μL L(−1)) CO(2) in outdoor, sunlit, environment-controlled chambers and performed a cross-switching of growth CO(2) concentration at the late-vegetative phase. Within 24 h, plants switched to high CO(2) showed a 15% and 23% decrease in rbcS mRNA, whereas plants switched to ambient CO(2) increased 27% and 11% in expanding and mature leaves, respectively. Ribulose-1,5-bisphosphate carboxylase/oxygenase total activity and protein content 8 d after the switch increased up to 27% and 20%, respectively, in plants switched to ambient CO(2), but changed very little in plants switched to high CO(2). Plants maintained at high CO(2) showed greater carbohydrate pool sizes and lower rbcS transcript levels than plants kept at ambient CO(2). However, after switching growth CO(2) concentration, there was not a simple correlation between carbohydrate and rbcS transcript levels. We conclude that although carbohydrates may be important in the regulation of rbcS expression, changes in total pool size alone could not predict the rapid changes in expression that we observed.