GROWTH, WATER RELATIONS AND SOLUTE COMPOSITION OF PHASEOLUS-VULGARIS L UNDER SALINE CONDITIONS

In this work, the influence of increasing external NaCl on relative growth rate, water relations and the degree of osmotic adjustment achieved by Phaseolus vulgaris plants have been studied. Both shoots and roots of plants grown in saline media were smaller after 13 days of saline treatment. Concentrations of NaCl of 25 mM and lower, although decreasing plant weight, did not appreciably affect relative growth rate of plants. The concentrations of both Cl- and Na+ in leaves significantly increased as the concentration of NaCl was increased in the nutrient solution. The concentration of K+ was also significantly increased with salinity, whereas leaf Ca2+ content remained unaffected. Plants exposed to NaCl concentrations of up to 50 mM did not differ from control plants in total sugars and proline concentrations. However, the presence of 100 mM NaCl in the external solution significantly increased total sugars and proline. The general tendency of organic acid concentrations was to decrease with salinity. The relative contribution of inorganic ions to the decrease in osmotic potential was 0.45 MPa, about 88%, whereas organic compounds contributed with 0.04 MPa, about 8%. The results are discussed in order to explain the inhibition of growth observed upon saline treatment as well as which solutes are implicated in the process of osmoregulation.