Effect Of Magnesium Levels On Growth Of Corn Under Cadmium Stress And Its Physiological Mechanisms

Cd is one of the most toxic heavy metals which farmland was contaminated with commonly. Research shows that the most area of farmland soil was contaminated with Cd in China. Cd has a strong biological mobility.In siol Cd pollution have had potential dangerous to safe production of agricultural products and human health. Magnesium is an essential nutrient element under normal growth conditions of the plant. It plays a number of crucial roles in plants photosynthesis and in plant defense response.In recent years, the number of researches on the effects of Mg in alleviating heavy metal poison is increasing, but it is no idear whether Mg could alleviate heavy metal poison, and the physiological processes and mechanisms of Mg in alleviating heavy metal toxicity are still far from clear.The corn was used in the studies. The effects of Mg on biomasses, oxidative stress, Cd distribution in corn, changement of mineral elements in corn, Photosynthetic and chlorophyll fluorescence characteristics were researched through water culture experiment. The major results and conclusions were summarized as follows:The results showed that under Cd stress, biomass of corn was reduced, the content of Cd was increased significantly, and Cd affects the absorption and transport of the mineral elements in Corn. Mg sufficiency reduced significantly biomasses of shoots, but apparently improved Cd contents; High Mg could improve biomasses of shoots obviously, but also significantly improved the Cd content. Under Cd stress, the effects of Mg levels on mineral element content in corn depended on the element type, plant parts and Mg2+concentration.Cd stress reduced the content of chlorophyll and carotenoid, suppressed hotosynthetic rate of corn. The effects of Mg sufficiency on the content of chlorophyll a and carotenoid were not obvious, but significantly reduced Chlorophyll b, obviously improved Chlorophyll a/b. And the effects of high Mg on the content of Chlorophyll b and a/b were not obvious, but significantly improved Chlorophyll a and carotenoid, thus obviously improved net photosynthetic rate, and reduced intercellular CO2concentration. Mg deficiency is more restrained photosynthetic of corn under Cd stress, Pn and Ci were all lower, and the effects of Mg deficiency on transpiration rate (Tr) and stomata conductance (Gs) are not obvious. Mg levels affect significantly PS â…¡ maximum photochemical efficiency (Fv/Fm), but Mg deficiency or high Mg obviously improved PS â…¡ potential activity, maintain a high activity of Light reaction center.Under Cd stress, the activities of superoxide dismutase (SOD) and catalase (CAT) significantly improved, on the contrary peroxidase (POD) reduced, and the content of MDA improved and increased the plant cell lipid membrane peroxidation. Mg sufficiency reduced the activities of SOD and the content of AsA, suppressed the antioxidant system in corn, but high Mg mitigate lipid peroxidation damage which were caused by Cd by improving the activities of CAT and the content of GSH and AsA.