Analysis by 13C Measurement on Mechanism of Cultivar Difference in Leaf Photosynthesis of Rice (Oryza sativa L.)

Abstract

Our previous paper showed that cultivar difference of flag leaf photosynthesis (LPS) in rice (Oryza sativa L.) was attributed to the difference in mesophyll resistance (rm). In this paper, we tried to divide rm into CO2 transfer resistance (rr) and CO2 fixation resistance (rc) for further analysis of rm by means of <? 3C determination of photosyntheti c products. In the heading time, rr, and rc occupied 14, and 58% in the total resistance, respectively, in average through 31 cultivars. This suggests that cultivar difference of LPS is mainly caused by the difference of r c. The percentage ratios of each resistance to the total one were maintained comparatively constant through the senescing process of the flag leaves. Moreover, the CO2 concentration in CO 2 fixating site showed almost the same values in different cultivars in a whole life span of a flag leaf. The rc showed a close correlation with ribulose-l,5-bisphosphate carboxylase/oxygenase (RubisCO) content. Carbonic anhydrase (CA) activity showed no correlation with rr, but showed positive correlation with rc. It was suggested that a mutual regulation system between CA activity and RubisCO activity could exist.