Alleviating Effects of Exogenous Glutathione, Glycinebetaine, Brassinosteroids and Salicylic Acid on Cadmium Toxicity in Rice Seedlings (Oryza Sativa)

A hydroponic experiment was conducted to study the ameliorative effects of 24 h pretreatment with exogenous glutathione (GSH), glycinebetaine (GB), brassinosteroids (BRs) and salicylic acid (SA) upon 50 μM cadmium (Cd) stress to rice seedlings. The results showed that Cd caused a significant reduction in seedling height, chlorophyll content and biomass, the activity of POD in stems, and shoot Mn, shoot/root Zn and root Cu concentration, but improved SOD and POD activities in leaves with elevated MDA accumulation and Fe concentration. Pretreatment with 100 μM GSH, GB or SA greatly alleviated Cd-induced growth inhibition and suppressed Cd-induced MDA accumulation. Compared with Cd alone treatment, pretreatment of GSH, GB and SA markedly increased chlorophyll content; reduced shoot Cd concentration, and GSH also decrease root Cd content. GSH, GB and SA pretreatments counteracted the pattern of alterations in certain antioxidant enzymes induced by Cd, e.g. significantly suppressed Cd-induced increase of leaf SOD activity, GB and BRs also significantly decreased leaf POD activity; GSH significantly elevated the depressed stem POD and SOD activities; and GB elevated stem SOD activity. Compared with Cd alone, GSH pretreatment significantly relieved Cd-induced reduction in Cu or increase in Fe concentration in leaves; GB pretreatment decreased Cd-induced Fe enhancement; SA pretreatment markedly increased shoot Fe, but reduced Mn concentration. Although BRs pretreatment increased plant dry biomass with no effect on chlorophyll content and MDA accumulation, significantly increased Cd concentration both in shoots and roots.