Regulation Of Cadmium Absorption And Tolerance By Gene Manipulation Of AtMGT1in Plant

The heavy metal enrichment ability of plant is related to the uptake and transport process of heavy metal in plant. In these processes, metal transporter protein plays an important role. Cadmium is one of the most toxic and non essential metals in the environment. No spedcific transport protein of cadmium was discovered in plant cell up to now, but researchers found it can go across membrane into plant cells by carrier or channel of other divalent cations such as Ca2+,Fe2+and Zn2+. AtMGTl gene is a transportation protein, which has high affinity with magnesium ions. It can not only transmembrane transport Mg2+, but also transport other ions such as Ni2+, Co2+and Fe2+. It also can improve the tolerance of plants for aluminum stress. In this study, the AtMGTl gene was introduced into ordinary tobacco through transgenic technology, and the growth, the Mg, Cd and trace metals absorption and transport of AtMGT1gene tobacco was studied at different Mg and Cd levels through solution culture experiment and soil culture experiment. Also, the changes of oxidation-antioxidation system and photosynthetic characteristics were investigated. The aim of our study was to explore the physiological mechanism of cadmium uptake and tolerance in AtMGT1gene tobacco. The main results are as following:The solution culture experiment results showed that under Cd stress, biomasses of two tobaccos were reduced, and Mg deficiency enhanced further inhibition of growth. Mg excess inhibited the growth of AtMGT1tobacco, but promoted the growth of WT tobacco.AtMGT1tobacco had higher biomass than WT tobacco at Mg deficiency and Mg sufficiency, and lower biomass at Mg excess condition. Under Cd stress, the Mg levels of two tobaccos were raised. There was a significantly inhibition at the Cd absorption and transport of tobacco with Mg obtained, and the inhibitory was more obvious at WT tobacco. The influences of trace metals in AtMGT1tobacco at different Cd and Mg levels were different because of the element type, plant parts and Mg concentration. The Cd, Mg and trace metals absorption and transport capacity of AtMGT1gene tobacco were stronger than WT tobacco.Under Cd stress, the photosynthetic pigment and photosynthesis fluorescent parameters of two tobaccos were decreased, and the photosynthetic rates (Pn) were suppressed. And the influence of Cd stress was more deeply to WT tobacco. The chlorophyll contents and photosynthesis fluorescent parameters decreased significantly at Mg deficiency, that made a stronger inhibitory effect of Pn. Mg excess increased the photosynthetic pigment and photosynthesis fluorescent parameters of WT tobacco, and promoted the Pn. But Mg excess had litter effect on chlorophyll a, carotenoid and PSII maximum photochemical efficiency (Fv/Fm), reduced the chlorophyll b and other photosynthesis fluorescent parameters significantly, that made a unconspicuous decrease of Pn. The photosynthetic pigment, photosynthesis fluorescent parameters and Pn of AtMGTl tobacco were higher than WT tobacco at all the treatments besides Mg excess.Under Cd stress, the contents of malondialdehyde (MDA), glutathione (GSH), ascorbate (AsA) and proline, and the activities of superoxide dismutase (SOD) and peroxidase (POD) were significantly increased, that means the two tobaccos were suffering from oxidative damage and activated the antioxization system. Mg deficiency further increased the oxidative damage. Under this situation, MDA, GSH, AsA and proline contents were significantly increased, SOD activity had no obvious change in two tobaccos, POD activity had a significantly increas in AtMGT1tobacco but no obvious change in WT tobacco. Mg excess slightly increased the MDA and GSH contents and POD activity of AtMGTl tobacco, significantly increased proline content, and significantly decreased AsA content and POD activity. In the meantime, the MDA content and SOD activity decreased, the GSH, AsA and proline contents and POD activity had no obvious change in WT tobacco under Mg excess. MDA contents of AtMGT1tobacco were significantly lower than that of WT tobacco, and SOD and POD activities were higher than that of WT tobacco at different Cd and Mg levels. GSH contents of AtMGT1tobacco were lower than that of WT tobacco, that may relate to the Cd concentration in cytoplasm.The results of soil culture experiment showed that under Cd stress, the biomasses of two tobaccos decreased, the Cd contents of two tobaccos significantly increased, and it had obvious influence on the elements absorption of tobacco. Under Cd stress, the Cd contents of AtMGT1tobacco were significantly higher than that of WT tobacco. And the Cd accumulation ability of AtMGT1tobacco was higher at high concentration Cd-contaminated soil. Under Cd stress, the enrichment factor of AtMGTl tobacco was bigger than that of WT tobacco. The AtMGTl tobacco could exert stronger enrichment performance of Cd, so it can be used as hyperaccumulator of Cd.The influences of Cd stress on absorption and transport of Mg2+, Fe2+, Mn2+, Cu2+and Zn2+were different between solution culture experiment and soil culture experiment. It showed that the ions absorption and transport at tobacco were affected by process-time, treat concentrations and growing environment. But at both solution culture experiment and soil culture experiment, the Mg2+, Fe2+, Mn2+and Zn2+absorption and transport capacity of AtMGTl tobacco were stronger than that of WT tobacco, and under Cd stress, the Cd2+absorption and enrichment of AtMGT tobacco were stronger than that of WT tobacco.