Abstract
Vacuolar (Na+, K+)/H+ antiporter transports Na+ and K+ from the cytoplasm to vacuoles using a pH gradient generated by two H+-pumps, vacuolar H+-ATPase (V-ATPase) and H+-inorganic pyrophosphatase (V-PPase). In barley, a salt-tolerant crop, salt stress and treatment with ABA and 2,4-D increased the activities of Na+/H+ antiporter and H+-pumps in tonoplast vesicles from roots. We isolated one gene ( HvNHX1) for the antiporter, one (HvVHA-A) for the catalytic subunit of V-ATPase, and two (HVP1 and HVP10) for V-PPase from barley. Salt and osmotic stresses and treatment with ABA and 2,4-D increased the expression of HVP1 in roots. The maximum level of HVP1 transcripts in response to these hormones was much higher than the levels of HVP10 and HvVHA-A transcripts. Furthermore, HvNHX1 expression changed in a pattern similar to that of the HVP1 expression, suggesting that the expression of HVP1 is co-ordinated with that of HvNHX1 in response to environmental changes.
