THE EFFECT OF SALINITY STRESS ON GROWTH, OSMOTIC ADJUSTMENT, NITROGEN METABOLISM AND ION ACCUMULATION BY A SALT RESISTANT AND A SALT SENSITIVE CULTIVAR OF BARLEY

CM 67 is a salt tolerant cultivar of barley which grows at higher external NaCl concentrations than Arivat, a salt sensitive cultivar. The salt tolerance of CM 67 may be a result of its ability to osmotically adjust more effectively than Arivat. The results show that nitrate uptake was tightly correlated to growth for both cultivars that CM 67 maintained higher nitrate uptake rates than Arivat in the presence of salinity. The reduction of nitrate into different organic nitrogenous compounds was unaffected by external NaCl and was apparently unrelated to plant salt tolerance. The salt tolerance of CM 67 was not directly correlated to its ability to accumulate betaine or proline (common nitrogenous osmotica). Both cultivars when exposed to the same external salt concentrations accumulated similar concentrations of proline and betaine. Increasing external NaCl concentrations increased growth inhibition but there was no obvious correlation between the extent of growth and nitrogenous osmotica accumulation, both between the two cultivars and within each cultivar at different external NaCl concentrations.;Both CM 67 and Arivat preferentially accumulated more proline and betaine in their meristematic tissue than in older tissues. There were, however, no differences between the levels of these compounds between different external NaCl concentrations within each cultivar and between the two cultivars. Both cultivars maintained higher potassium:sodium ratios in meristematic tissues than in older tissues but CM 67 maintained higher ratios at higher external NaCl concentrations. Arivat was unable to maintain high potassium:sodium ratios at high external NaCl.;All the results indicated that protection of the meristematic portion of the plants by maintaining high potassium:sodium ratios and high innocuous organic osmotica were important for plant survival under NaCl stress. Other criteria for example, the ability to adjust cell size and cytoplasmic:vacuolar ratio may also be important for plants growing in saline conditions.;Phosphate uptake was unaffected by external NaCl in both cultivars. Sulphate uptake was barely detected in both cultivars. Sodium and chloride uptake were directly proportional to the external NaCl concentration and to the duration of plant exposure to NaCl. There were no differences in sodium or chloride uptake between the cultivars. Potassium uptake was inversely proportional to the external NaCl in both cultivars with no differences between the cultivars.