Unveiling the Mechanisms Underpinning Alleviation of Mercury Toxicity by Static Magnetic Field Treatment in Soybean

The toxic metal mercury (Hg) exhibits inhibitory effects on several plant physiological processes. Multiple attempts have been tried in the past to lessen the phytotoxic effects of Hg in plants. However, so far no information is available on the possible beneficial effects of magnetopriming in soybean plants subjected to Hg toxicity. In the present study, the soybean seeds were magnetoprimed by static magnetic field (SMF) of 200 mT for 1 h to assess the influence of magnetopriming on germination and early growth features of seedlings under Hg toxicity. Reduction in germination percentage and growth parameters such as seedling length, fresh and dry weight of seedlings and vigor indices of seedlings emerged from unprimed seeds under different concentrations of mercuric chloride (0.0, 0.05, 0.1 mM HgCl2), indicated the negative effects of Hg toxicity on seedling growth at all the concentrations of HgCl2. However, magnetopriming has been found to be effective in alleviating the Hg stress. Along with hydrogen peroxide (H2O2) and nitric oxide (NO), the activities of total amylase, protease, and nitrate reductase (NR) were elevated in seedlings emerged from SMF-primed seeds in non-stress as well as Hg toxicity conditions. The proline and malondialdehyde (MDA) contents were increased with the increasing Hg concentrations in the seedlings emerged from unprimed seeds; however, magnetopriming reduced their content. Antioxidant enzyme system revealed higher activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GuPOX) along with higher antioxidants (total ascorbate, AsA and reduced glutathione, GSH content) after SMF priming in comparison to unprimed seeds during germination at all the concentrations of HgCl2 used. It is conceivable that the positive effect of magnetopriming is mediated by the reduced lipid peroxidation and enhancement of H2O2 and NO levels along with the activation of antioxidant defense system to protect the soybean seedlings against Hg toxicity during seed germination.