Exogenous salicylic acid regulates reactive oxygen species metabolism and ascorbate-glutathione cycle in Nitraria tangutorum Bobr. under salinity stress.

Abstract

The effect of 0.5-1.5mM salicylic acid (SA) on modulating reactive oxygen species metabolism and ascorbate-glutathione cycle in NaCl-stressed Nitraria tangutorum seedlings was investigated. The individual plant fresh weight (PFW) and plant dry weight (PDW) significantly increased under 100mM NaCl while remained unchanged or decreased under 200-400mM NaCl compared to the control. Superoxide anion (O2·-), hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS), reduced ascorbate (AsA), dehydroascorbate (DHA), reduced glutathione (GSH) and oxidized glutathione (GSSG) increased whereas the ratios of AsA/DHA and GSH/GSSG decreased under varied NaCl treatments. Ascorbate peroxidase (APX) and glutathione reductase (GR) activities were enhanced while dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities remained unvaried under 100-400mM NaCl stresses. In addition, exogenous SA further increased PFW, PDW and root/shoot ratio. SA effectively diminished O2·- accumulation. H2O2 and TBARS decreased under 0.5 and 1.0mM SA treatments compared to those without SA. 0.5mM of SA increased while 1.0 and 1.5mM SA decreased APX activities. DHAR activities were elevated by 0.5 and 1.0mM SA but not by 1.5mM SA. MDHAR and GR activities kept constant or significantly increased at varying SA concentrations. Under SA treatments, AsA and GSH contents further increased, DHA and GSSG levels remained unaltered, while the decreases in AsA/DHA and GSH/GSSG ratios were inhibited. The above results demonstrated that the enhanced tolerance of N. tangutorum seedlings conferred by SA could be attributed mainly to the elevated GR and DHAR activities as well as the increased AsA/DHA and GSH/GSSG ratios.