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 (r_m). In this paper, we tried to divide r_m into CO₂ transfer resistance (r_m) and CO₂ fixation resistance (r_c) for further analysis of r_m by means of δ¹³C determination of photosynthetic products. In the heading time, r_r, and r_c 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...

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 (r_m). In this paper, we tried to divide r_m into CO₂ transfer resistance (r_m) and CO₂ fixation resistance (r_c) for further analysis of r_m by means of δ¹³C determination of photosynthetic products. In the heading time, r_r, and r_c 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 CO₂ fixating site showed almost the same values in different cultivars in a whole life span of a flag leaf. The r_c showed a close correlation with ribulose-l,5-bisphosphate carboxylase/ oxygenase (RubisCO) content. Carbonic anhydrase (CA) activity showed no correlation with r_r, but showed positive correlation with r_c. It was suggested that a mutual regulation system between CA activity and RubisCO activity could exist.