Xylem ion balance in tomato plants under alkali stress

Abstract

In many areas of China, alkalinity (high pH) had strongly limit crops productivity. Control of ion loading into the xylem has been repeatedly named as a crucial factor determining plant salt tolerance. To investigate the role of roots in alkali tolerance of tomato, we tested the ion balance in root xylem of alkali stressed tomato plants. Two alkaline salts (NaHCO3 and Na2CO3) were mixed in a 9:1 molar ratio as the alkali stress treatments. Under alkali stress condition or control condition, xylem sap samples were collected by cutting plant stems near to cotyledon vestige, and then all mineral elements in excreted xylem sap were measured. The results showed that alkali stress decreased the concentrations of K + , Ca 2+ , Cl - , and NO3 - in the xylem sap, and increased Na + concentration, Na + /K + and Na + /Ca 2+ . Low alkali stress (pH 8.6 and 22.5 mM Na + ) and strong alkali stress (pH 8.8 and 45 mM Na + ) have almost same pH but different Na + ; however, under both stresses ion concentrations in the xylem sap were similar, indicating that the uptakes of inorganic ions were inhibited by high-pH but not by Na + .