EFFECT OF SALINITY ON THE PLASMA-MEMBRANE ATPASE FROM TOMATO (LYCOPERSICON-ESCULENTUM MILL) LEAVES

Experiments were conducted to determine if salt-induced changes in the plasma-membrane H+-ATPase could account for decreased shoot growth in Lycopersicon esculentum Mill. cv Heinz 1350. The plasma membrane was isolated from mature and young leaves of untreated (control) and salt- stressed leaves using the aqueous polymer two-phase technique. Analysi s of ATP hydrolytic activity showed that salt stress reduced the V-max of H+-ATPase specific activity in mature leaves but had no effect in young, growing leaves. These findings are consistent with measurements of adenine nucleotide levels. We observed a large decrease in adenyla te energy charge (AEC) in mature leaves following salt stress. AEC in young leaves remained unaffected. In addition, a dramatic increase in K, the adenylate kinase mass action ratio, from 0.18 to 1.53 was measu red in mature leaves following salt stress. These results indicate-tha t salt stress did not reduce growth of young, growing leaves by decrea sing H+-ATPase activity and support our earlier hypothesis that salt s tress affects mature leaves and, as a consequence, their ability to su pply essential metabolites for growing regions of both shoot and roots .