Interactive effects of salicylic acid and nitric oxide on soybean plants under NaCl salinity

The effects of salicylic acid (SA), sodium nitroprusside (SNP), a nitric oxide donor, and their combination (SA+SNP) on some physiological parameters of 23-day-old soybean seedlings grown under saline and nonsaline conditions were studied. The changes in the leaf area, shoot fresh and dry weights, contents of chlorophylls and carotenoids, amounts of MDA and hydrogen peroxide showed that the addition of 100 mu M SA and/or 100 mu M SNP markedly declined the oxidative damage to soybean plants induced by 50 and 100 mu M NaCl. Our results proved that combined action of SA and nitric oxide donor significantly activated catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX), which contributed to the decay of H2O2 in soybean leaves under NaCl toxicity. The protective action of (SA+SNP) against saltinduced oxidative damage was often more efficient than effects of SA and SNP alone. We also observed that the accumulation of proline was apparently accelerated by these substances under salt stress. As well, it was observed that the interaction between SA and nitric oxide had synergistic effects in decreasing of the damages induced by NaCl salinity.