Salinity stress effects on growth and nitrate assimilation in bean seedlings likely to be mediated via nitric oxide

Background : Salinity stress usually imposes adverse effects on plant systems, but the severity depends upon plant species, growth status and genotype, nutritional and environmental conditions etc. Present study analyses salinity effects on growth and in vivo nitrate reductase activity (NRA) in Phaseolus vulgaris seedlings to work out the mechanism. Results : Supply of 10-200 mM NaCl with 10 mM KNO 3 for 24 h in continuous light reduced the overall growth of the bean seedlings, with perfect -ve correlation for seedling weight, root length and shoot length. Salinity effect with 10 mM NH 4Cl was lesser and with 10 mM NH 4NO 3 was intermediary. NaCl treatment with 10 mM KNO 3 reduced the fresh wt of the root as well as shoot tissue but increased in vivo NRA exerting strong correlation and more prominent effect in the root tissue. Very high NaCl concentration prominently increased NRA at 1, 10 and 50 mM KNO 3 showing inverse gradation in effect. Salt treatment with NH 4NO 3, reduced the in vivo NRA of the root tissue, but the stress parameters, like proline and peroxidase were increased. Conclusions : The salinity stress effects on NRA are less severe with NH 4+, more prominent for root and more effective at low NO 3- concentration. Inverse correlation between decrease in fresh mass and increase in NRA with salinity suggests the involvement of NR in the synthesis of nitric oxide and the observed effect of stress is the balance of two factors reduced assimilatory effect and increased nitric oxide stress.