Salinity effects on hydraulic conductance, lignin content and peroxidase activity in tomato roots

Abstract

The effects of salinity on the hydraulic conductance of tomato roots, content of lignin-like polymers and peroxidase activity were studied. Seedlings of tomato, Lycopersicon esculentum L. cv. Pera were grown hydroponically and salt treatments (100 mM NaCl) were given for 10 days, 1 day or 40 min. Hydraulic conductance was measured by pressurization. The activity of syringaldazine oxidase, a peroxidase (EC 1.11.1.7) associated with lignification, was visualized in tissue prints of main roots and its specific activity was measured in root extracts. In tissue prints, syringaldazine oxidase activity was detected both in the xylem as well as in the subepidermal layers, which are presumably suberized, suggesting that the enzyme may also participate in the synthesis of suberins. Long- and short-term salinity treatments significantly decreased root hydraulic conductance (P<0.01). However, the content of lignin-like polymers and the activity of syringaldazine oxidase were similar in roots of control and salinized plants. The effects of salinity on root hydraulic conductance may be mediated by effects on symplasmic rather than apoplastic structures. Only a partial reversal of the salinity-associated decrease in pressure-induced flux was obtained with b-mercaptoethanol in short-term treatments.