Effects of zinc-nano oxide, salicylic acid and sodium nitroprusside on physiological properties, antioxidant enzyme activities and secondary metabolites of Viola odorata under drought stress

One of the most important abiotic stresses and limiting factors (closing pores, lack of CO2 entry, reduced photosynthesis, and reduced yield) of plant products around the world is water-deficit stress. This study aimed to examine the water deficit stress and foliar application with anti-stress compounds (ASC) on characteristics of Viola odorata. The study was carried out as a factorial experiment based on a randomized complete design. The factors consisted of water deficit and the foliar application of ASC at six levels [zinc-nano oxide (ZnO, 1000 and 1500 mg l–1), salicylic acid (SA, 200 and 300 mg l–1), and sodium nitroprusside (SNP, 200 and 300 μM)], and the control. The water deficit reduced the leaf water potential, cell membrane stability, and the shoot and root fresh weight but increased electrolyte leakage and soluble sugar accumulation. However, foliar applications, particularly SA and SNP, positively affected the measured parameters. The activities of superoxide dismutase and guaiacol peroxidase at all three field capacity levels were higher in the plants treated with SA and SNP than in the control and plants treated with ZnO. In sum, using 200 mg l–1 of SA as a foliar application, in addition to improvement of the growth and developmental conditions of the aromatic violet plant, moderated the adverse effects of water deficit stress and increased the plant resistance to water deficit stress. Based on the results, the application of SA, SNP, and ZnO reduced electrolyte leakage and enhanced the plant’s resistance to water deficit by increasing the compatible osmolyte accumulation and antioxidant enzyme activity.