Characteristics of ribulose-1,5-bisphosphate carboxylase and C4 pathway key enzymes in flag leaves of a super-high-yield hybrid rice and its parents during the reproductive stage

A newly-developed super-high-yield two-line hybrid rice (Oryza sativa L.) LiangYouPeiJiu (LYPJ) together with its paternal line Wumang 9311 (WM9311) and maternal line Peiai 64S (PA64S) were used as experimental materials. The activities of C4 pathway photosynthetic enzymes, i.e. phosphoenolpyruvatecarboxylase (PEPcase), NADP-malic enzyme (NADP-ME), NADP-malate dehydrogenase (NADP-MDH), pyruvate phosphate dikinase (PPDK) and the key C3 pathway enzyme–ribulose-1,5-bisphosphate carboxylase (RuBPcase), as well as soluble protein were assayed during the days after emergence (DAE) of flag leaves. The results indicated that C4 pathway enzymes were expressed differently during the flag leaf's span of life. The activity of PEPcase, NADP-MDH, and PPDK were increased with leaf age after full expansion, reached the peak at around 32 DAE, and then fell down significantly, and the activity of NADP-ME increased before 23 DAE and decreased earlier than other C4 enzymes, at 32 DAE, indicating that NADP-ME may be more sensitive to senescence than other C4 enzymes. The activity of RuBPcase was significantly higher in LYPJ than that in its parents during the whole life span of flag leaves. The decrease in RuBPcase activity was greater than that in soluble protein content. The onset of loss of RuBPcase activity (11 DAE) occurred earlier than that of soluble protein content (23 DAE). In comparison, there was no significant difference in C4 pathway enzymes between LYPJ and its parents.