Exogenous nitric oxide (NO) increased antioxidant capacity of cucumber hypocotyl and radicle under salt stress

Excessive accumulation of reactive oxygen species (ROS) under salt stress can cause oxidative damage, nitric oxide (NO) is considered as a functional molecule in alleviating salt stress to plants through modulating antioxidant metabolism. In the present experiment, effects of sodium nitroprusside (SNP), a NO donor, on the growth, and antioxidant capacity of cucumber hypocotyls and radicles as well as root tip ultrastructure were studied under 100 mM NaCl stress. NaCl treatment significantly induced accumulation of H2O2 and thiobarbituric acid-reactive substances (TBARS) in cucumber hypocotyls and radicles, and application of 100 μM SNP stimulated ROS-scavenging enzymes and increased α,α-diphenyl-β-picryllhydrazyl (DPPH) scavenging activity, chelating activity of ferrous ions and hydroxyl radical (OH) scavenging activity, resulting in lower lipid peroxidation induced by NaCl stress. The ultrastructure of the root tip cells was investigated, NaCl stress induced disturbance of mitochondria and the cell wall, and SNP treatment alleviated the ultrastructure disturbance induced by NaCl stress. The above effects of SNP were reversed by addition of hemoglobin (a NO scavenger), which indicated that the function of SNP alleviating lipid perioxidation in NaCl-treated cucumber hypocotyls and radicles depended on NO. Therefore, it can be concluded that the increasing antioxidant capacity by NO might be greatly responsible for its function in alleviating the inhibition of cucumber hypocotyls and radicles growth and cell ultrastructure damage by salt stress.

► Exogenous NO alleviated the inhibited growth of cucumber hypocotyls and radicles by NaCl.
► Exogenous NO increased antioxidant enzyme activities of cucumber hypocotyls and radicles under NaCl stress.
► Exogenous NO increased antioxidant capacity of cucumber hypocotyls and radicles under NaCl stress, which greatly depended on increasing contents of GSH and AsA.
► Exogenous NO protected the mitochondria and cell wall of cucumber root tips from damage induced by NaCl stress.