Abstract
Rice cultivar, Akenohoshi produces heavier dry matter than those of Nipponbare. The main causal factor is the relatively smaller decrease in the rate of photosynthesis during the ripening stage in Akenohoshi. Cytokinin levels in xylem sap are high in Akenohoshi. However, the mechanisms in the suppression of the decrease in photosynthetic rate are not clear. The effect of exogenous cytokinin on the rate of photosynthesis and its causal factors were investigated in Nipponbare with or without cytokinin (BA).
The decrease in leaf photosynthetic rates was smaller in BA-treated plants than those of control plants. The carboxylation efficiency was higher in BA-treated plants. The decreases in levels of Rubisco and rbcL and rbcS mRNAs were smaller in BA-treated plants. These results indicate that the higher rate of photosynthesis with BA-treated plants is caused by the higher carboxylation efficiency due to the higher levels of Rubisco brought by higher rbcL and rbcS transcripts.
