Maximum Quantum Yields of O_2 Evolution in C_4 Plants under High CO_2 : GROWTH AND DEVELOPMENT : ENVIRONMENTAL AND STRESS RESPONSES

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The quantum yields of photosynthetic O_2 evolution were measured in 15 species of C_4 plants belonging to three different decarboxylation types (NADP-ME type, NAD-ME type and PEP-CK type) and 5 species of C_3 plants and evaluated relative to the maximum theoretical value of 0.125 mol oxygen quanta^<-1>. At 25℃ and 1% CO_2, the quantum yield in C_4 plants averaged 0.079 (differences between subgroups not significant) which was significantly lower than the quantum yield in C_3 plants (average of 0.105 for 5 species). This lower quantum yield in C_4 plants is thought to reflect the requirement of energy in the C_4 cycle. For the C_4 NADP-ME type plant Z. mays and NAD-ME type plant P. miliaceum, quantum yields were also measured over a range of CO_2 levels between I and 20%. In both species maximum quantum yields were obtained under 10% CO_2 (0.105 O_2 quanta^<-1> in Z. mays and 0.097 O_2 quanta^<-1> in P. miliaceum) indicating that at this CO_2 concentration the quantum yields are similar to those obtained in C_3 plants under CO_2 saturation. The high quantum yield values in C_4 plants under very high CO_2 may be accomplished by direct diffusion of atmospheric CO_2 to bundle sheath cells, its fixation in the C_3 pathway, and feedback inhibition of the C_4 cycle by inorganic carbon.
日本植物生理学会の論文