The Study Of The Magnetic Field On The Growth Of Mung Bean Seedlings Under Cd Stress And Its Mechanism

Biomagnetism is new and interdisciplinary subject, it study magnetism of matter and the connection and affection between magnetic field and organisms. A lot of researches show magnetic field treatment can mobilize the regulation ability of plant, stimulate its vigour, improve metabolism physiologically. It can also alleviate the inhibited effect of adversity stress, such as drought, salt stress, low temperature. Cadmium (Cd2+) stress as one of the heavy metal stress could harm plants, affect their development and yield and quality. Now, information is still lacking regarding the effects and mechanisms of magnetic field on the growth of plant under heavy metal stress. We investigated the effects of magnetic field on the growth of plant under Cd2+ stress. In order to understand the mechanisms of magnetic field on the growth of plant under Cd2+ stress, we investigated effects of magnetic field on the membrane lipid peroxidation and photosynthesis of mung bean seedings under Cd2+ stress. The main results were presented as follows:1. Compared to control treatment,0.6T magnetic field treatment could raise mung bean seeding height and main root length, and the fresh and dry weight of the over-ground part and roots were also increased. By the contrast, when the mung bean seedings were under Cd2+ stress, growth of mung bean seedings was inhibited, and the fresh and dry weight of the over-ground part and roots were also decreased. However, we found the above inhibited effect of Cd2+ stress could be clearly alleviated by 0.6T magnetic field treatment. The results indicated that magnetic field treatment can not only improve the growth of mung bean seedings under normal circumstance but also alleviate the inhibited effect of Cd2+ stress on growth of mung bean seedings.2. Compared to control treatment, Cd2+ stress respectively increased the activities of SOD, CAT and POD in leaf and root of mung bean seedings, and at the same time raised the content of H2O2. Membrane lipid peroxidation was intensified, which was represented by the increase of MDA.0.6T magnetic field treatment did not influence the activities of POD in leaf and root of mung bean seedings, but the activities of SOD, CAT were increased to some extent, and caused a decrease of MDA content and H2O2 level in leaf and root of mung bean seedings. Compared to Cd2+ stress alone, treatment of MF+Cd2+ caused a decrease of MDA content and H2O2 level, and at the same time, more increases in SOD, CAT, POD activities in leaf and root of mung bean seedings. The results showed that magnetic field treatment might decrease the levels of reactive oxygen species, and then inhibit membrane lipid peroxidation in leaf and root of seedings under normal circumstance and Cd2+ stress by enhancing the activities of the three antioxidant enzymes, which may be one of the mechanisms that magnetic field treatment improved the growth of mung bean seedings under normal circumstance and alleviated the inhibited effect of Cd2+ stress on growth of mung bean seedings.3 Compared to control treatment,0.6T magnetic field treatment enhanced net photosynthetic rate, stomatal conductance, intercellular CO2 concentration and transpiration rate respectively, but stomatal limitation was not changed by the magnetic field. These results showed that the magnetic field treatment-induced improvement of photosynthesis in mung bean seedings was mainly caused by stomatal factor. However, Cd2+ stress caused the decreases of net photosynthetic rate, stomatal conductance, transpiration rate, while intercellular CO2 concentration was enhanced and stomatal limitation was not changed respectively, showing that the inhibitive effect of Cd2+ stress on photosynthesis of mung bean seedings was mainly caused by nonstomatal factors.0.6T magnetic field treatment also enhanced net photosynthetic rate, stomatal conductance and transpiration rate, but reduced intercellular CO2 concentration and did not change stomatal limitation of mung bean seedings under Cd2+ stress respectively, which indicated that the magnetic field treatment enhanced the ability of photosynthesis of mung bean seedings under Cd2+ stress, so as to alleviate Cd2+ stress-induced inhibitive effect on photosynthesis in mung bean seedings. The above results further indicated that the other reason of promoting the growth of mung bean seedings by magnetic field treatment under normal condition and Cd2+ stress is the enhancement of photosynthesis of seedings by the magnetic field. Although under the two conditions, the magnetic field-induced improvement of photosynthesis in mung bean seedings was the results of both stomatal and nonstomatal factors, the stomatal limitation is dominant under normal condition, and the nonstomatal limitation becomes the dominant one under Cd2+ stress.