The role of vacuolar malate-transport capacity in crassulacean acid metabolism and nitrate nutrition. Higher malate-transport capacity in ice plant after crassulacean acid metabolism-induction and in tobacco under nitrate nutrition

Anion uptake by isolated tonoplast vesicles was recorded indirectly via inc reased H+-transport by H+-pumping of the V-ATPase due to dissipation of the electrical component of the electrochemical proton gradient, Delta mu (H+) , across the membrane. ATP hydrolysis by the V-ATPase was measured simultan eously after the Palmgren test. Normalizing for ATP-hydrolysis and effects of chloride, which was added to the assays as a stimulating effector of the V-ATPase, a parameter, J(mal)(rel), of apparent ATP-dependent malate-stimu lated H+-transport was worked out as an indirect measure of malate transpor t capacity. This allowed comparison of various species and physiological co nditions. J(mal)(rel) high in the obligate crassulacean acid metabolism (CA M) species Kalanchoe daigremontiana Hamet et Perrier, it increased substant ially after CAM induction in ice plant (Mesembrysnthemum crystallinum), and it was positively correlated with NO3- nutrition in tobacco (Nicotina taba cum). For tobacco this was confirmed by measurements of malate transport en ergized via the V-Prase. In ice plant a new polypeptide of 32-kD apparent m olecular mass appeared, and a 33-kD polypeptide showed higher levels after CAM induction under conditions of higher J(mal)(rel). It is concluded that tonoplast malate transport capacity plays an important role in physiologica l regulation in CAM and NO3- nutrition and that a putative malate transport er must be within the 32- to 33-kD polypeptide fraction of tonoplast protei ns.