Physiological function of water channels as affected by salinity in roots of paprika pepper

The sap flow (Jv) and the osmotic pressure‐dependent hydraulic conductance (L 0 ) of detached exuding root systems from paprika pepper plants (cv. Albar) were measured. Plants stressed with NaCl (30 m M ) and with six times the macronutrients of the Hoagland nutrient solution (6×HNS) were compared with controls grown in complete Hoagland nutrient solution. Jv of +NaCl and +6×HNS plants decreased markedly, but recovered to values similar to those of controls after removal of the treatments. Hydraulic conductance L 0 was always less in NaCl plants than in controls and 6×HNS. A total increase in the ion concentration of the xylem (except Na + and Cl − ) was observed with both treatments. In control and 6×HNS plants, HgCl 2 treatment (50 μ M ) caused a sharp decline in L 0 to values similar to those of NaCl‐stressed roots, but were restored by treating with 5 m M dithiothreitol (DTT). However, in NaCl roots only a slight effect of Hg 2+ and DTT was observed. In each treatment, there was no difference in the flux of K + into the xylem after HgCl 2 and DTT application. The results suggest that NaCl decreased L 0 of the roots by reducing either the activity or abundance of Hg‐sensitive water channels. The putative reduction in water‐channel function of NaCl‐treated plants did not seem to be due to the osmotic effect.