Comparative effects of indole acetic acid and salicylic acid on oxidative stress marker and antioxidant potential of okra (Abelmoschus esculentus) fruit under salinity stress

Plants suffer osmotic and ionic stress under high salinity due to salt accumulation in the various cells. In this study, the effects of phytohormones on seedling and fruit antioxidant enzymes were investigated. Okra seeds were germinated in polyethylene bags in a screen house under various salt conditions with or without application of compounds that can minimize the harmful effects of this environmental stress. The okra seeds (genotype LD 88) were pre-soaked with salicylic acid (10−2, 10−4,or 10−6 mM), indole acetic acid (0.4, 0.5, or 0.6 mM) or distilled water (control) for 12 h under natural environmental conditions, followed by 0, 50, 100 or 200 mM NaCl treatment. Results showed that activity levels of antioxidant enzymes significantly (p < 0.05) increased with increasing NaCl concentration. Increased in antioxidant activities were especially noticeable at high salinity levels (150 and 200 mM NaCl) the exception of catalase (CAT) and glutathione peroxidase (GPX) that showed low activities at high salinity level (200 mM) when compared to a control plant (0.0 mM NaCl). But CAT activity increased more in the presence of salicylic acid, and indole acetic acid at 10−6 mM and 0.4 mM respectively while GPX and superoxide peroxidase (SOD) activities were poorly expressed in the two treatments when compared to the control group. Increased in the 2,2-diphenyl-1-picryhydrazyl (DPPH) radical scavenging capacity in this study was as a result of increased in the activity of antioxidant enzymes in the plant, which mitigate the destructive effects of reactive oxygen species in the plant.