Abstract
Four C4 photosynthetic enzymes (PEPC, PPDK, NADP-MDH, NADP-ME) were overexpressed in rice leaves. The overexpression of PEPC alone slightly suppressed photosynthesis, while co-expression of PPDK, MDH, and ME in addition to PEPC restored photosynthesis, although it caused slight stunting. Comparison of three different double (PEPC+PPDK, PEPC+ME, MDH+ME) and one triple (PEPC+PPDK+ME) transformants indicated that the overexpression of PEPC acted to suppress photosynthesis, and the co-expression of PEPC and ME caused stunting. PPDK and MDH are active only in the daytime while PEPC and ME are active day and night. It is thus likely that the co-expression of PEPC and ME results in consumption of once fixed carbon at night and under weak light illumination. PEPC becomes more active at night than in the daytime in rice leaves. The stunting of the quadruple transformant observed in this study might be unique to rice.
