Stimulation of plasma membrane h⁺-transport activity in barley roots by salt stress

Plasma membrane vesicles were prepared from barley roots (Hordeum vulgare cv. Kikaihadaka) using the phase partitioning method. H⁺-transport activity could be measured without membrane inversion treatment, since the plasma membrane vesicles showed a latency value of approximately 50% for the activity. Following the exposure to NaCl, alterations of the plasma membrane H⁺-ATPase and H⁺-transport activity were investigated. After barley roots were treated with 200 mol m⁻³NaCl for 1 d, both plasma membrane H⁺-ATPase activity and H⁺-transport activity assayed in the presence of nitrate were reduced as compared with those of control roots. However, in the salinized roots, the H+ -transport activity measured with chloride was higher than that of control roots, though the H⁺-ATPase activity was lower. These results suggest that the permeability of the plasma membrane to chloride may increase by salt stress.