Abstract
Nitric oxide (NO), a small diffusible, ubiquitous bioactive molecule, acts as prooxidant as well as antioxidant, and also regulates remarkable spectrum of plant cellular mechanisms. The present work was undertaken to investigate the role of nitric oxide donor sodium nitroprusside (SNP) and/or calcium chloride (CaCl2) in the tolerance of excised mustard leaves to salt stress. After 24 h, salt stressed leaves treated with SNP and/or CaCl2, showed an improvement in the activities of carbonic anhydrase (CA) and nitrate reductase (NR), and leaf chlorophyll (Chl) content, leaf relative water content (LRWC) and leaf ion concentration as compared with the leaves treated with NaCI only. Salinity stress caused a significant increase in H2O2 content and membrane damage which is witnessed by enhanced levels of thiobarbituric acid reactive substances (TBARS) and electrolyte leakage. By contrast, such increases were blocked by the application of 0.2 mM SNP and 10 mM CaCl2 to salt stressed leaves. Application of SNP and/or CaCl2 alleviated NaCl stress by enhancing the activities of antioxidative enzymes viz. superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) and by enhancing proline (Pro) and glycinebetaine (GB) accumulation with a concomitant decrease in H2O2 content, TBARS and electrolyte leakage, which is manifested in the tolerance of plants to salinity stress. Moreover, application of SNP with CaCl2 was more effective to reduce the detrimental effects of NaCI stress on excised mustard leaves. In addition to this, ameliorating effect of SNP was not effective in presence of NO scavenger cPTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxidel. To put all these in a nut shell, the results advocate that SNP in association with CaCl2 plays a role in enhancing the tolerance of plants to salt stress by improving antioxidative defence system, osmolyte accumulation and ionic homeostasis. (C) 2012 Elsevier Inc. All rights reserved.