Characteristics of leaf photosynthesis in Chinese F1 hybrid rice [Oryza sativa] cultivar, Shanyou 63

Leaf photosynthetic rate (Pl) of Shanyou 63 (SH), a Chinese F1 hybrid cultivar with exceedingly high yield, was evaluated in comparison with those of two Japanese leading pure-line cultivars (JC), Nipponbare and Koshihikari. The three cultivars were grown in pots from early to pre-heading stage. Stomatal and mesophyll conductances, chlorophyll content, soluble protein content and ribulose 1,5-bisphosphate carboxylase (RuBPCase) activity were measured. The results obtained are as follows: 1) Pl of SH was constantly higher than those of JC through the growth stage. Particularly at the early growth stage, the difference in Pl between SH and JC was large: SH and JC showed 26.98 and 21.15 micro-molm(-2)s(-1), respectively. 2) The high Pl of SH at the early growth stage depended on both high stomatal and mesophyll conductances, while at the pre-heading stage the high mesophyll conductance was the main cause of increasing Pl. 3) Contents of chlorophyll and soluble protein of SH were significantly lower than those of Jc, and there was no significant difference in RuBPCase activity between cultivars. 4) Thus sH, having low contents of chlorophyll and soluble protein in leaf, and a high Pl and maintained an almost similar level to those of JC in RubPCase activity. A higher efficiency in nitrogen use for photosynthesis is one of the features observed in this cultivar.