Tonoplast H+-ATPase activity in barley roots is regulated by ATP and pyrophosphate contents under NaCl stress.

The changes in ATP and PPi contents in roots under NaCl stress, and the effect of PPi on tonoplast H(+)-ATPase activity were studied with two barley cultivars differing in salt tolerance. The results showed that tonoplast H(+)-ATPase activity in salt-tolerant barley cultivar "Tanyin 2" roots increased obviously under NaCl 200 mmol/L (containing half-strength Hoagland solution) for 2 d, and decreased gradually. Tonoplast H(+)-PPase activity always decreased under NaCl stress. For salt-sensitive barley cultivar "Kepin 7", both tonoplast H(+)-ATPase and H(+)-PPase activities decreased during NaCl stress, as compared with control(grown in half-strength Hoagland solution), ATP content of "Tanyin 2" roots increased under NaCl stress for 2 d, and decreased on 4 d after NaCl stress, as compared with control. In "Kepin 7" roots, ATP accumulation was inhibited during NaCl stress. Pyrophosphate (PPi) content increased slightly both in "Tanyin 2" and "Kepin 7" roots under NaCl stress. Tonoplast H(+)-ATPase activity was inhibited competitively by PPi. These results indicated that the increase in rate of ATP accumulation might be essential for the stimulation of tonoplast H(+)-ATPase activity induced by NaCl. The decrease in ATP content and the inhibition of PPi might result in the decrease of tonoplast H(+)-ATPase activity in barley roots under NaCl stress.