Tonoplast H+-ATPase in response to salt stress in Populus euphratica cell suspensions

A salt-tolerant stable cell suspension culture from Populus euphratica, which is the foremost tree to survive and form forests in the deserts of western China, has been established from calli generated from plantlets. We have characterized the tonoplast H+-ATPase activity and studied the responses of this enzyme to the salt stress. The tonoplast H+-ATPase from P. euphratica was sensitive to the same inhibitors (NEM, DCCD, Nitrate, Bafilomycin A,) as the tonoplast H+-ATPases from other plants. The kinetics of ATP-driven proton pumping by tonoplast vesicles from salt free and NaCl treated cell suspension cultures were compared. It was found that NaCl stimulated the proton pumping activity. Immunodetection of the enzyme showed that the increased activity could be due to increases in protein amount in the tonoplast induced by NaCl. In addition, the proton pumping was dependent upon the divalent cation and Mg2+ was essential for enzyme activity. The tonoplast H+-ATPase from P. euphratica also showed substrate specificity to ATP. Results, to our knowledge, provide the first direct evidence for the existence of a tonoplast H+-ATPase from cell suspensions of P. euphratica, which plays an important role in the salt tolerance of this plant. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.