Reducing the effect of salinity and lead on garlic (Allium sativum) seedling roots by improving oxidant defence under selenium and hydrogen sulfide

Selenium and hydrogen sulfide can alleviate the adverse effects of oxidative stress on plants by improving the oxidative defense system. In order to improve the oxidative defense system of garlic under lead and salinity stress by selenium and hydrogen sulfide, a factorial experiment was carried out using selenium and hydrogen sulfide in a completely randomized design with three replications. Experimental treatments included sodium chloride at three levels of zero, 25 and 75 mM, lead at three concentrations of zero, 10-5 and 10-3 M lead nitrate as well as stress ameliorators in three levels (5 mg / L sodium selenate, 200 μm sodium hydrogen sulfide and control). The results showed that with increasing salinity and lead concentration, a significant decrease in root length and dry weight was observed. In the treatment of 10-5 M lead under 75 mM salinity, the activity of antioxidant enzymes superoxide dismutase, ascorbate peroxidase and catalase were 4.44, 11.76 and 10.47%, respectively, and compared to the zero lead stress and 75 mM, salinity was improved with selenium application. In general, sodium selenate and sodium hydrogen sulfide decreased the uptake of lead in root tissue whereas increased the length and dry weight of roots under salinity stress at a concentration of 10-5 M, but at a concentration of 10-3 M lead, this effect was not observed. Overall results showed that the positive effect of selenium on hydrogen sulfide during salinity stress was more evident in reducing the negative effects of lead. It seemed that selenium suppressant improved the growth parameters of garlic roots under salinity stress and low lead concentrations by reducing lead absorption and increasing the activity of antioxidant enzymes.