The interaction of sodium and calcium chlorides and light on growth, potassium nutrition, and proline accumulation in callus cultures of Medicago sativa L.

SUMMARY Callus cultures, established from cultivars of Medicago sativa L., Dupuits and Spredor2, were used to investigate salt‐induced changes in metabolism. With increase in NaCl concentration there was a progressive reduction in growth rate but this effect was ameliorated by increase in the Ca2+ concentration. The concentration of Na+ in the callus increased in response to NaCl in the medium but not proportionally, while the K+ concentration was lowest in calli grown at the highest NaCl concentration. High Ca2+ partially reversed the salt‐induced decrease in K+, so overall, the effect of Ca2+ was to decrease the Na+/K+ ratio. Proline concentration in the callus increased in response to NaCl. With callus cultures grown in the absence of supplemental NaCl there was no correlation between growth and proline concentration, whereas at the highest NaCl concentration used (150 mol m−3) there was a strong positive correlation between growth and proline concentration of individual calli. Increased Ca2+increased the proline concentration in callus of both cultivars, and at the highest salt concentration resulted in higher proline concentration and increased growth. It is suggested that proline accumulation is important for cell growth only when a certain level of salt‐stress is attained, and this level will depend on the presence or absence of other protectant mechanisms in the tissue.