Photosynthetic enzyme activities and immunofluorescence studies on the localization of ribulose-1,5-bisphosphate carboxylase/oxygenase in leaves of C3, C4, and C3−C4 intermediate species of Flaveria (Asteraceae)

Abstract

Summary Activities of ribulose-1,5-bisphosphate carboxylase (rubisco), phosphoenolpyruvate carboxylase (PEPC), aspartate aminotransferase, alanine aminotransferase, NADH-malate dehydrogenase, NADPH-malate dehydrogenase, NAD-malic enzyme, NADP-malic enzyme, and pyruvate phosphate dikinase (PPDK) were measured in leaf extracts of Flaveria cronquistii (C 3 ), F. pubescens, F. anomala (C 3 −C 4 ), F. brownii, F. palmeri, F. trinervia , and F. australasica (C 4 ). The two C 3 −C 4 intermediate species show activities of PEPC, both aminotransferases, NADPH-malate dehydrogenase, NADP-malic enzyme, and PPDK intermediate between those of C 3 and C 4 Flaveria species. The Km values of rubisco for CO 2 exhibit distinct differences with higher values for the C 4 species. PPDK is light activated reaching its maximum activity at noon in F. brownii and, in contrast, very early after the beginning of the light phase in F. pubescens . PEPC from both F. palmeri, F. trinervia , and F. australasica is activated about twofold by NADH but there is no effect to the enzyme of all other Flaveria species. This activation might be a more general feature of PEPC from NADP-malic enzyme type C 4 plants. An immunofluorescence investigation of the intercellular compartmentation of rubisco revealed an intermediate distribution of this enzyme in leaves of F. pubescens and F. anomala . Typical immunofluorescence patterns with nearly exclusive localization of rubisco in the mesophyll or bundle sheath cell chloroplasts, respectively, were found in the C 3 and C 4 Flaveria species. The data are discussed with respect to the evolution of C 4 photosynthesis from C 3 photosynthesis via C 3 −C 4 intermediate types of photosynthetic carbon assimilation.