(NA+-K+)-STIMULATED ATPASE IN LEAVES OF C4 PLANTS - POSSIBLE INVOLVEMENT IN ACTIVE-TRANSPORT OF C4 ACIDS

Leaves of three C4 plants, Setaria italica, Pennisetum typhoides, and Amaranthus paniculatus possessed five- to ten-fold higher activities of a (Na+-K+)-dependent ATPase than those of two C3 plants, Oryza sativa and Rumex vesicarius. Na+-K+ ATPase from leaves of Amarathus exhibited an optimal pH of 7·5 and an optimal temperature of 35 °C. It required 40 mM K+ and 80 mM Na+ for maximal activity. Ouabain partially inhibited (Na+-K+)-dependent ATPase activity in leaves of C4 plants. Ouabain also blocked the movement of label from initially formed C4 acids into end products in leaves of only C4 plants, Setaria and Amaranthus but not in a C3 plant, Rumex. We propose that Na+-K+ ATPase may mediate transfer of energy during active transport of C4 acids from mesophyll into the bundle sheath. © 1978 Oxford University Press.