Plasma membrane H+-ATPase activity is involved in adaptation of tomato calli to NaCl

A tomato (Lycopersicon esculentum Mill. cv, Pera) callus culture tolerant t o NaCl was obtained by successive subcultures of NaCl-sensitive calli in me dium supplemented with 50 mM NaCl, NaCl-tolerant calli grew better than NaC l-sensitive calli in media supplemented with 50 and 100 mM NaCl, Analysis o f callus ion content showed a strong increase in Na+ and Cl- both in NaCl-t olerant and -sensitive calli grown in media containing NaCl for one subcult ure. Cells from NaCl-tolerant calli showed a higher H+ extrusion activity t han those from NaCl-sensitive calli grown for one subculture in the presenc e of NaCl, The inhibition of H+ extrusion by NaCl-sensitive cells was corre lated with an inhibition of microsomal vanadate-sensitive H+-ATPase (EC 3.6 .1.35) and ATP-dependent H+ transport, while the stimulation of H+ extrusio n by cells tolerant to 50 mM NaCl was correlated with an increase in plasma membrane ATP-dependent H+ transport. The increase of ATP-dependent H+ extr usion in plasma membranes isolated from 50 m;M NaCl-tolerant calli was not a result of stimulation of a vanadate-sensitive ATP hydrolytic activity or an increase in passive permeability to H+, Relative to NaCl-sensitive calli , plasma membrane H+-ATPase from calli tolerant to 50 mM NaCl showed a lowe r g, for Mg2+-ATP. Our results indicate that tolerance of tomato calli to 5 0 mM NaCl increases the affinity of plasma membrane Hf-ATPase for the subst rate ATP and stimulates the H+-pumping activity of this enzyme without modi fying its phosphohydrolytic activity.