Alleviation of Adverse Effects of Ambient UV Stress on Growth and Some Potential Physiological Attributes in Soybean (Glycine max) by Seed Pre-treatment with Static Magnetic Field

The effect of seed pre-treatment with a static magnetic field (SMF) of 200 mT for 1 h on the impact of ambient UV (280-400 nm) stress was tested using soybean var. JS-335 seeds. The SMF-pre-treated and untreated seeds were sown in plastic nursery bags placed in iron mesh cages covered with polyester filters that cutoff UV-B (< 315 nm) and UV-A/B (< 400 nm) radiations, transmitted all the ambient UV or without filters. The results of solar UV exclusion suggested that ambient UV caused reduction in growth, nitrogen, and carbon metabolism which ultimately reduced the yield of soybean seedlings, whereas SMF-pre-treatment increased plant height, leaf area, biomass accumulation with higher Lb, and hemechrome content in the root nodules, and improved the PS II efficiency and rate of photosynthesis both in the presence of solar UV components as well as under exclusion of solar UV as compared to untreated seeds. The amount of ROS like hydrogen peroxide (H2O2) and the activity of antioxidant enzymes like superoxide dismutase (SOD), glutathione reductase (GR), and guaiacol peroxidase (POD) assayed in the leaves of soybean were higher in the plants grown under ambient UV as compared to the exclusion of solar UV. Whereas under ambient UV stress, the plants that emerged from SMF-treated seeds showed lower amount of H2O2 and lesser activities of antioxidant enzymes SOD, GR, and POD as compared to untreated seeds. Thus, reduction in the H2O2 content and antioxidant enzyme activities after SMF-pre-treatment and UV exclusion indicated that solar UV components exert a significant stress on soybean plants. The levels of UAS were also decreased by both exclusion of UV and SMF-treatment. Reduction in the production of UAS indicated a changed pattern of metabolism leading to improved primary metabolism. The results indicate that exclusion of solar UV components and SMF-pre-treatment eliminates the need for defense against the ambient UV stress. Comparing SMF-treated groups with their respective untreated group, the remedial effects of SMF were found to be more striking on overall growth, nitrogen metabolism, and photosynthetic performance even in the presence of ambient UV stress. Consequently, SMF-pre-treatment ameliorated the ambient UV stress, so that the plants do not have to divert their metabolic energy for detoxification of ROS produced under UV stress. Thus, SMF-pre-treatment can be effectively used for alleviation of adverse effect of ambient UV stress and improve the yield of crop plants.