Dynamic regulation of the root hydraulic conductivity of barley plants in response to salinity/osmotic stress

Salinity stress significantly reduces the root hydraulic conductivity (Lp_r) of several plant species including barley (Hordeum vulgare). Here we characterized changes in the Lp_r of barley plants in response to salinity/osmotic stress in detail using a pressure chamber. Salt-tolerant and intermediate barley cultivars, K305 and Haruna-nijyo, but not a salt-sensitive cultivar, I743, exhibited characteristic time-dependent Lp_r changes induced by 100 mM NaCl. An identical response was evoked by isotonic sorbitol, indicating that this phenomenon was triggered by osmotic imbalances. Further examination of this mechanism using barley cv. Haruna-nijyo plants in combination with the use of various inhibitors suggested that various cellular processes such as protein phosphorylation/dephosphorylation and membrane internalization appear to be involved. Interestingly, the three above-mentioned barley cultivars did not exhibit a remarkable difference in root cell sap osmolality under hypertonic conditions, in contrast to the case of Lp_r. The possible biological significance of the regulation of Lp_r in barley plants upon salinity/osmotic stress is discussed.