Comparative Studies on C4 and C3 Photosynthetic Systems: Effect of Metabolic Inhibitors and Biochemical Intermediates on Carbon Metabolism

Abstract

The effect of several metabolic inhibitors and biochemical intermediates on photosyntheticcarbon metabolism was examined in Setaria italica (malate utilising C 4 plant), Amaranthus paniculatus (asparate utilising C 4 plant) and Rumex vesicarius (C 3 plant). The inhibition by MgCl 2 , KNC, PGA and 6-phosphogluconate and stimulation by ribulose diphosphate (RuDP) in Setaria and Amaranthus (and not in Rumex ) affirmed the role of RuDP carboxylase in mediating the movement of label in C 4 plants. The negligible effet of salicylaldoxime in all three plants suggested the independence of label-movement from cyclic photophosphorylation. The suppression of '4C-movement by ouabain indicated the possible role of an ATPase in active transport of C 4 acids during C 4 photosynthesis. The negligible effect of DCMU on 14 C-transfer in Setaria in contrast to remarkable inhibition of the same in Amaranthus suggested the existence of an alternative source of reducing power (NADPH 2 ) in Setaria , which is presumed to be NADP malic enzyme.