ION DISTRIBUTION IN LEAVES OF VARYING AGE IN SALT-TOLERANT LINES OF ALFALFA UNDER SALT STRESS

Two lines of alfalfa (Medicago sativa L.), a salt-tolerant AZ-Germ Salt II and a salt-sensitive Mesa Sirsa, were grown for three weeks in solution culture containing 0 or 100 mol/m(3) sodium chloride (NaCl) in half-strength Hoagland nutrient solution. Distribution of cations and chloride (Cl) in the leaves of varying ages was determined. The older leaves (age-dependent) of both lines contained more sodium (Na) in the laminae and petioles than the younger leaves at the salt treatment, whereas the reverse was true for potassium (K) in the laminae. Age-dependent Cl distribution was only found in the laminae of AZ-Germ Salt II. Distribution of calcium (Ca) in the lamina and petioles was strongly age-dependent in both lines, but such a pattern was not found for magnesium (Mg) concentrations. AZ-Germ Salt II accumulated considerably higher concen- trations of Na and Cl in the laminae compared with Mesa Sirsa. The lower Na and Cl concentrations in the laminae of Mesa Sirsa were due to relatively higher accumulation of these ions in the stems. It is concluded that distribution of Na, Cl, and Ca in the leaf laminae is age dependent. Salt tolerance in alfalfa is related to inclusion of Na and Cl in the leaf laminae.