H(+)ATPase activities of tonoplast-enriched vesicles from non-treated and NaCl-treated jojoba roots

Tonoplast-enriched vesicles prepared by discontinuous sucrose density gradient centrifugation of microsomal membranes from jojoba (Simmondsia chinensis (Link) Schneid.) roots grown with or without 100 mM NaCl were analysed for nitrate-sensitive ATPase and ATP-dependent H+-pumping activities as well as for total phospholipid and free sterol content. The inhibitor sensitivity and pH optimum of the ATP hydrolysis and H+-pumping activities match quite closely those reported for the tonoplast ATPase of other plant materials, NaCl treatment increased the V-max of the nitrate-sensitive ATPase for ATP hydrolysis and of the initial rate of ATP-dependent H+-pumping but did not cause alteration of the apparent K-m values. The magnitude of the increase in ATPase activity in response to NaCl is about 25%. Palmitic, oleic and linoleic acids were the three major fatty acid components of total phospholipids of tonoplast fraction, whereas the most abundant free sterols were campesterol, stigmasterol and, above all, sitosterol. The percentages of phospholipid fatty acids and free sterol molecular species were not altered whereas the content of these lipids increased when roots were grown in 100 mM NaCl. Further studies will examine the regulation by NaCl of the tonoplast ATPase, and the role of different phospholipid classes of enriched-tonoplast fraction in NaCl stress response.