Evaluation of salicylic acid, zinc Nano-oxide and sodium nitroprusside pre-treatments on some physiologic parameters and enzymatic activity of sweet violet under water-deficit stress conditions

Sweet violet (Viola odorata) is a perennial herbaceous plant with ornamental and medicinal properties. The purpose of this study was to investigate the effect of different levels of water-deficit and spraying with salicylic acid, sodium nitroprusside and zinc Nano-oxide on physiological parameters, secondary metabolites and enzymatic activity of sweet violet. Factorial experiment in completely randomized design was performed with two factors; water-deficit stress at 3 levels (55, 65 and 85% of field capacity or FC of pot soil) and sprays including salicylic acid (200 and 300 mg/l), zinc Nano-oxide (1000 and 1500 mg/l) and sodium nitroprusside (200 and 300 μM) in three replications. The results showed that with increasing water-deficit stress, the amount of phenolic compounds, proline and phytol, as well as the percentage of secondary metabolites, antioxidant enzyme activity and plasma membrane stability increased. The highest phenolic compounds (57.07 mg/galic acid/g D.W.) and proline content (52.47 mg/kg F.W.) were obtained in the treatment of 300 μM sodium nitroprusside at 55% of field capacity. The highest activity of superoxide dismutase (1.94 EU/mg/pro./min), catalase (0.198 EU/mg/pro./min) and polyphenol oxidase (0.248 EU/mg/pro./min) were obtained in treatments of 200 mg/l salicylic acid and 200 and 300 μM sodium nitroprusside, respectively, in 55% FC. The highest amount of phytol (2.87%) belonged to the control treatment in 55% of FC. The highest amount of sodium (28.60 mg/kg) and phosphorus (0.60 mg/kg) in control plants in 55% stress and potassium (4.29 mg/kg), iron (306 mg/kg F.W.) and dry matter percentage of shoots (26.23) and roots (27.60) was observes in spraying with 1000 mg/l of zinc nanoparticles in stress 85%, 1500 mg/l zinc oxide in stress 65%, 200 μM salicylic acid in stress 85% and 1000 mg/l of zinc Nano-oxide in 55% stress, respectively. Totally, the use of 200 mg/l of salicylic acid as spray, in addition to improving the growth and developmental conditions of sweet violet, decreased the negative effects of water-deficit stress and increased plant resistance to water-deficit.