The Role of Brassinosteroids and Salicylic Acid on Spinach Growth and Cadmium Accumulation under Cadmium Stress

A greenhouse investigation was performed to examine the influence of salicylic acid and brassinolide on growth and cadmium accumulation of spinach under cadmium stress conditions at Nutrition Research Center, Department of Food Hygiene and Quality Control, Shiraz University of Medical Sciences during 2020 using a factorial as randomized complete block design with three replications. Experimental treatments were including salicylic acid (0, 0.5 and 0.75 mM), and brassinolide (0, 0.5 and 0.75 μM) and cadmium (0, 300 and 600 μM). The results showed that cadmium stress enhanced the concentrations of malondialdehyde (MDA), hydrogen peroxide (H2O2) and electrolyte leakage (EL) as well as reduced the spinach biomass. Under Cd stress conditions, the activities of antioxidant enzymes and the concentrations of proline and carbohydrates increased. Also, application of SA and Br considerably reduced the MDA and H2O2 content and EL, in contrast, elevated the activities of antioxidant enzymes and osmolytes content in Cd-stressed spinach plants, however; the positive effects of SA were high when applied with Br. It was found that the cadmium content in the root was greater than that of spinach leaves. Under 600 μM cadmium stress conditions, application of 0.5 mM salicylic acid, 0.75 mM salicylic acid, 0.50 μM brassinosteroid, 0.75 μM brassinosteroid, 0.5 mM salicylic acid+ 0.5 μl brassinosteroid, 0.5 μM salicylic acid /0 0 mM+ 0.75 μM brasinosteroid, 0.75 μM salicylic acid+ 0.50 μM brasinosteroid and 0.75 μM salicylic acid reduced the cadmium content 12.68, 13.68, 13.93, 22.13, 25.37, 30.09, 30.34 and 45.02% respectively in leaf, as well as 6.53, 10.13, 11.76, 18.30, 26.30, 32.67, 33.34 and 42.81% respectively in root compared to the non-use of these hormones. In conclusion, alleviation of Cd stress by seed priming and foliar application of Br and SA was associated partially with enhanced the activity of the antioxidant system, increase the accumulation of proline and carbohydrates, as well as improve cell membrane stability. Generally, supplementation with Br and SA had a significant effect on reducing the accumulation of cadmium and improving quality and quantity of spinach under Cd-stress.