Nitric oxide (NO), an endogenous signaling molecule, is involved in various physiological processes and stress responses in plants. In the present research, Pyrodwarf pear (Pyrus communis) rootstocks were grown by nutrient solution to investigate the effects of sodium nitroprusside (SNP) application as an NO donor at 0, 0.1, 0.5, and 1 mM levels on plant stress tolerance, content of main polyamines, physiological reactions, and activity of CAT and APX enzymes under NaCl stress condition at 0, 50, 100, and 150 mM concentrations. Exogenous NO significantly increased endogenous NO content of leaves, height of the plants and relative water content (RWC) of leaves while it decreased malondialdehyde (MDA) content. NaCl stress increased the content of putrescine (Put) and spermine (Spm), and exogenous NO resulted in a further increase the content of Spm in plant leaves under NaCl stress. Pyrodwarf pear rootstocks significantly showed higher content of proline and antioxidant activity under NaCl stress, and NO treatment further increased the content of proline and antioxidant activity in plants exposed to NaCl stress. The activity of antioxidant enzymes including catalase (CAT) and peroxidase (POD) increased in plants under NaCl stress, and exogenous NO further induced those antioxidant enzyme activities. Exogenous NO resulted in the enhancement of Spm content and plants with higher Spm content exhibited high levels of antioxidant activity and proline content under NaCl stress, indicating the beneficial effects of exogenous NO under salinity conditions. NO improved the tolerance of Pyrodwarf pear rootstocks under NaCl stress by regulating the content and the ratio of polyamines. تفاصيل المقالة