INTERCELLULAR COMPARTMENTATION OF IONS IN BARLEY LEAVES IN RELATION TO POTASSIUM NUTRITION AND SALINITY

X-ray microanalysis was used to determine the distributions of several nutrient elements between vacuoles of epiderma an mesophyll cells in barley leaves and these distributions were related to shoot nutrient c oncentrations. Under the growth conditions used, P was found only in m esophyll vacuoles, never in the epidermis. In contrast, Cl and Ca were located almost exclusively in the epidermis while K and Na were more evenly distributed between the two cell types. The compartmentation of Ca and Cl in the epidermis was maintained over a wide range of tissue concentrations of these ions. In particular, Cl was excluded from the mesophyll of salt-grown barley until the tissue concentration reached about 170 mol m-3 and then it appeared in the vacuoles of these cells , but only at low concentrations. In contrast, Na was not excluded fro m the mesophyll of salt-grown or K-deficient barley and there was evid ence that this ion was preferentially accumulated in the mesophyll. Nu trients were evenly distributed between the adaxial and abaxial epider mal layers, except K which was at slightly higher concentrations in th e adaxial epidermis. There was considerable variation in the concentra tions of ions in adjacent epidermal cells. The results indicate that i ntercellular compartmentation of nutrients occurs in barley leaves and the role of this phenomenon in responses to nutrient deficiencies and salinity is discussed.