Mechanism Of Cadmium Tolerance In Different Tobacco Cultivars

Cadmium is one of the most mobile and toxic heavy metals in environment. Tobacco has high ability to accumulate cadmium. So far studies have focused on toxic effect of Cd on tobacco while variance analysis on physiological and biochemical response of different tobacco toward Cd stress is in lack of research and the key control mechanisms of producing variance is still in need of further study. In this study, base on the Nicotina tabacum L. var. Xanthi and Nicotina tabacum L. var. Guiyan 11 which are the different tolerance tobacco varieties of cadmium, the differences of growth, accumulate and transport under cadmium in the two varieties and transport and nutrition distribution element under cadmium have been discussed; the different physiological mechanisms on different tobaccos response cadmium have been discussed; according to the differences of cadmium distribute changes in subcellular of roots and leaves of these two tobaccos, cell-compartmentation mechanism has been studied; according to the DNA electrophoresis, the possible approach of physiological metabolizable and dominate mechanisms response cadmium have been studied. It offers references of physiological and molecular mechanisms on plant how to tolerant cadmium, and it is very important to restore contaminated soil of cadmium.The results showed: there are different responses in these two tobaccos on cadmium, the growth of Xanthi have obvious dose effect on cadmium, but Cd restrain the growth of Guiyan 11, so Xanthi has more resistent ability of cadmium than Guiyan 11; root has more obviously response cadmium, and it is more sensitive than leaves.The studies which based on the difference accumulation and transport of economic on cadmium in these two tobaccos tell us: roots have tolerance ability which can prevent cadmium carrying to shoot, and the organization district of Xanthi is more obvious; following the cadmium threaten, the concentration of cadmium in roots ascend in these two tobaccos, but Xanthi ranged higher than Guiyan 11, so Xanthi has more able to accumulate cadmium; the difference of cadmium concentration in shoot was significantly visible, because cadmium content in Nicotina tabacum L. var. Xanthi shoots are obvious higher than Guiyan 11, but it was not visible in roots cadmium content in these tobaccos;Following cadmium, the transport rates of two tobaccos were descended, and it was also be founded that organization district of Xanthi is more obvious than Guiyan 11, so we think it is one of possible mechanisms of Xanthi to resistant high cadmium concentration; cadmium can restrain the content of bleedings of Nicotina tabacum L. var. Xanthi, but promote that of Guiyan 11, and the content of cadmium in bleedings were ascend in both of them, and comparing control treatment, the cadmiun transport rate of Guiyan 11 is higher than Xanthi in bleedings, and transport rate of calcium and magnesium were decended under cadmium, and kalium ascended in low treatment and descended in high treatment, and all of calcium, magnesium, kalium had obvious different in two varieties.According to the nutrition element studies in these varieties, the distributing of constant and microelement changed under cadmium, and it was different in two varieties. The dambification of DNA in two varieties indicated that, the colour of DNA was becaming darker following time of exposure, from white to brown to dark brown to black, and Guiyan 11 was more sensitive and deep toxicosis than Xanthi; intimidate of 25μmol/LCd²⁺ can damage DNA of tobacco, and the more time of exposure, the DNA break down deeper and smaller. After 72h under 25μmol/LCd²⁺, the damage was most serious; and the concentration more high, the damage was more serious.According to the antioxidation system responses cadmium stress in these two tobaccos leaves, the malondialdehyde(MDA) of two tobaccos had the same change to cadmium, frist increase then decrease, but MDA of Xanthi was higher than Guiyan 11, and they had significant different; superoxide dismutase(SOD) have significant different in two tobaccos, and SOD of Xanthi was higer than Guiyan 11, so Xanthi can hold higher SOD; peroxidase(POD) also have significant different in two tobaccos, and higher treatment can hold higher POD activities in Xanthi, but the POD of Guiyan 11# was decreased on cadmium, so it is one of possible physiological mechanisms of Xanthi to resistant cadmium; the change of catalase(CAT) in these tobaccos also had significant differences, those were low treatment restrained CAT activities in both two varieties, and high treatment increased CAT activities of Xanthi but decr eased in Guiyan 11, so it is also one of possible physiological mechanisms of Xanthi to resistant cadmium. Synthetically, containing SOD, POD, CAT, under low cadmium siol stress, SOD was very important in Xanthi and Guiyan 11, on the other hand, whiles in high cadmium stress, POD and CAT are vital in antioxidant system of Xanthi, but they are not visible in Guiyan 11.The studies of protein changes to cadmium of two tobacco varieties suggested: the change of soluble protein content are not obviously in these two tobaccos, Guiyan 11 changed a little, and Xanthi decreased in 3mg/Kg cadmium stress, but increase in 10mg/Kg cadmium stress and beyond control. This may because the indiscerptible protein break to soluble protein as cadmium stress, and it indicated that the protein change is complex to cadmium, and it related to concentration and varieties. Compare these two tobaccos, Xanthi have more detoxifcate capability. In the protein electrophoresis, both of two tobaccos protein changed but some protein weaken and laken and no new protein came out in Xanthi; in 5μmol/L Cd²⁺ treatment 120KD protein came out and 50KD protein disappeared in Guiyan 11, and it suggested that protein in roots of Guiyan 11 changes bigger than Xanthi. Cadmium can induce new protein and laken or weaken some protein, and the new protein may resistant toxic of cadmium.Cell wall was the dominate region in the subcellular, and the obstruct ability of Xanthi was better than that of Guiyan 11 in cell wall to stop the cell organelles destroy by cadmium, so cell-compartmentation mechanism of Xanthi was more significant. Beside cell wall, cell organelles were the important region in roots and liquid was the important region in leaves, and the responses of two tobaccos were not the same. It was similar content of cadmium in cell organelles and liquid, but liquid in leaves of Guiyan 11 had more cadmium than cell organelles. Because liquid came from cytoplasm and vacuole, besides cell wall, vacuole was the important regions in subcelluar of Guiyan 11.