ENHANCED ACTIVITY OF TONOPLAST PYROPHOSPHATASE IN NACL-GROWN CELLS OF DAUCUS-CAROTA

Anthocyanin containing carrot cells, capable of growing in the presence of NaCl or sorbitol, were used to study the effect of salt and osmotic treatment during growth on the activity of the K+-stimulated (tonoplast) pyrophosphatase in microsomal fractions from cells grown +/- 50 mM NaCl or +/- 100 mM sorbitol. This enzyme activity was markedly stimulated by NaCl treatment and unaffected by sorbitol treatment. The dependence on monovalent cations and the apparent affinity for K+ of the salt-increased pyrophosphatase activity were the same as those of the pyrophosphatase activity of the untreated cells. By comparison, the activities of the vanadate-sensitive (plasma membrane) ATPase and of the nitrate-sensitive (tonoplast) ATPase were unaffected by both NaCl and sorbitol treatments. The results suggest that tonoplast pyrophosphatase could play a role in the mechanism of salt tolerance.