The K + / H + antiporter LeNHX2 increases salt tolerance by improving K + homeostasis in transgenic tomato

The endosomal LeNHX2 ion transporter exchanges H + with K + and, to lesser extent, Na + . Here, we investigated the response to NaCl supply and K + deprivation in transgenic tomato ( S olanum lycopersicum   L .) overexpressing LeNHX2 and show that transformed tomato plants grew better in saline conditions than untransformed controls, whereas in the absence of K + the opposite was found. Analysis of mineral composition showed a higher K + content in roots, shoots and xylem sap of transgenic plants and no differences in Na + content between transgenic and untransformed plants grown either in the presence or the absence of 120 m m NaCl . Transgenic plants showed higher Na + / H + and, above all, K + / H + transport activity in root intracellular membrane vesicles. Under K + limiting conditions, transgenic plants enhanced root expression of the high‐affinity K + uptake system HAK5 compared to untransformed controls. Furthermore, tomato overexpressing LeNHX2 showed twofold higher K + depletion rates and half cytosolic K + activity than untransformed controls. Under NaCl stress, transgenic plants showed higher uptake velocity for K + and lower cytosolic K + activity than untransformed plants. These results indicate the fundamental role of K + homeostasis in the better performance of LeNHX2 overexpressing tomato under NaCl stress.