Abstract
C4 plants show higher activities of cyclic electron flow around PSI (CEF) than C3 plants. It is suggested that CEF produce ATP to drive C4 metabolism. To clarify how CEF enhanced with the development of C4 pathway during evolutional process from C3 to C4 photosynthesis, we investigated CEF activity, expression levels of proteins involved in CEF and thylakoid membrane structure using genus Flaveria containing C3, C4, C3-C4 intermediate and C4-like species. NDH activity was higher in C4-like species than in C3-C4 intermediate species, as well as the NDH-H expression level. On the other hand, CEF activity estimated from the P700 oxidation rate was higher in C4 species than in C4-like species. Drastic difference in expression level of PGR5 involved in FQR activity and grana stacking ratio of bundle sheath chloroplasts were also observed in those species. These results suggested that the NDH pathway developed earlier than the FQR pathway in C4 evolution. Taken together with evidence that expression of C4 metabolic enzymes was already elevated in C3-C4 intermediate species, we assume that CEF was enhanced in a later process of development of C4 cycle.
