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 concentrations. Under the growth conditions used, P was found only in mesophyll 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 from the mesophyll of salt-grown or K-deficient barley and there was evidence that this ion was preferentially accumulated in the mesophyll. Nutrients were evenly distributed between the adaxial and abaxial epidermal layers, except K which was at slightly higher concentrations in the adaxial epidermis. There was considerable variation in the concentrations of ions in adjacent epidermal cells. The results indicate that intercellular compartmentation of nutrients occurs in barley leaves and the role of this phenomenon in responses to nutrient deficiencies and salinity is discussed.