NaCl-induced changes in vacuolar H+-ATPase expression and vacuolar membrane lipid composition of two shrub willow clones differing in their response to salinity

It has been suggested that vacuolar H⁺-ATPase (V-H⁺-ATPase) plays a pivotal role in salt stress, and salt stress could modulate the expression and enzyme activity of V-H⁺-ATPase. In this work, salt modulation of V-H⁺-ATPase and tonoplast fatty acid compositions were evaluated in two shrub willow clones differing in salt tolerance after 3, 6 and 12 days of treatment. The results showed that the activity of V-H⁺-ATPase was regulated in tissue and clone specifically under NaCl stress. In the leaves of salt-tolerant clone 2345, treatment with 100 mM NaCl increased V-H⁺-ATPase activity first and then decreased it at day 12, while V-H⁺-ATPase activity was stimulated in the roots by NaCl during the treatment time. In contrast, V-H⁺-ATPase activity reached the highest value at day 3 in the leaves of salt-sensitive clone 2367 and then it decreased. Accumulation of Na⁺ in the vacuole was observed in parallel with increase in V-H⁺-ATPase activity. Western blot and immunofluorescence analysis of V-H⁺-ATPase subunit E revealed that the protein content varied in parallel with V-H⁺-ATPase activity. Moreover, a decreased unsaturated fatty acids ratio to saturated ones together with an increased V-H⁺-ATPase activity was detected in the roots of salt-tolerant clone 2345 at day 12. Altogether, it suggested that the induction of V-H⁺-ATPase expression and increase in the saturation of tonoplast fatty acids as a homeostatic mechanism for shrub willow to cope with salt stress.