Studies On The Accumulation Characters And Influence Mechanisms Of Cadmium In Tobacco

The uptake and accumulation of cadmium in tobacco has some regularity. On the one hand,cadmium poisoning affected by the content and chemical speciation of cadmium in different parts oftobacco; on the other hand, it affected by external environmental factors. After provening cadmiumaccumulation and uptaking by tobacco, we can have a better methord to regulate the cadmiumabsorption by tobacco, and find a way to reduce the cadmium poisoning to tobacco. In this study, potexperiment and hydroponic test combinated to study the accumulation characteristics of cadmium bytobacco and the distribution of major chemical state in different part of tobacco. The result describes theeffects of cadmium on the growth and physiology of tobacco, and through the electron microscopyobserved at the cellular level, reveals the effects of cadmium on the physiological growth of tobacco.Our study find the regulatory effects of pH, temperature and Zinc on cadmium accumulation. Our aim isproviding a theoretical basis for the production of low hazard tobacco. and preventing cadmiumpollution.1The results of cadmium accumulation and absorption test showed that cadmium uptake bytobacco has a certain regularity. With the cadmium uptake by tobacco seedlings, the content of cadmiumat the first reduced and then increased, while finally stabilized. The rate of cadmium uptake by tobaccodeclined first then rise. cadmium content in tobacco leaves was significantly higher than that in thestems and roots. Under the control treatment, cadmium content showed as: root> stem> leaf. Beforethe tobacco harvest, the cadmium content in tobacco leaves showed as: lower leaves> middle leaves>upper leaves. Tobacco cadmium accumulation rate increased with the increasing of cadmiumconcentration.2The sensitivity of cadmium in tobacco varieties presented differently. Different cadmiumconcentrations had a greater impact on photosynthetic performance of tobacco, and has a obviousdifference between the different tobacco varieties. However, the photosynthetic performance of the fourtobacco varieties were drastically reduced when cadmium content is at64mg/kg, in combination withother indicators, we can initially concluded64mg/kg cadmium concentration is most lethalconcentration to tobacco. The presence of cadmium accumulation characteristics in different tobaccovarieties were same: lower leaves> middle leaves> upper leaf> root, stem. The change of cadmiumcontent in stem and root due to the variety and growing period. With the improvement of the cadmiumcontent, cadmium content in parts of all kind of tobacco were increased, The accumulation of cadmiumof the four varieties of tobacco were more or less same, however, zhongyan100has a better cadmiumtolerance. The content of cadmium chemical forms was different in different part of tobacco. In thelower leaves, cadmium was mainly binded to deionized water, in small leaves, buds and upper levels thecontent of this form of cadmium is little. In the stalk, the cadmium content in xylem is more than that inphloem. Xylem can transport and deposite cadmium. There are cadmium in phloem showed thatcadmium can be extracted through the phloem and transport to other parts of the tobacco. 3The forms of cadmium in different tobacco varieties were different. Compared to all threesafflower tobacco, the cadmium in different parts of zhondyan100was mainly binded to deionizedwater and sodium chloride. Combined with the front study about the accumulation of cadmiumcharacteristics we can identify zhongyan100has a high cadmium tolerance. Compared to terms andleaves, the acetic acid extractable form was more binded in the roots of he three safflower tobacco. Thisindicated that the root was the main organ of tobacco to deposite cadmium. while the leaf is the organwhich was the most heavily poisoned by cadmium. The forms of cadmium in rustica tobacco wassignificantly different to the common tobacco, there was more cadmium binded with deionized water,but the actual observation, its physiological effects to growth was not the most serious of all. So weindicated that rustica tobacco has higher cadmium tolerance. At the same time, at the roots the cadmiumwas mainly binded with acetic acid.4At the control treatment, cadmium are mainly concentrated in the stems of tobacco, with theincrease of the cadmium concentration, cadmium in leaves was increased, but cadmium is still mainlyaccumulated in the roots and stems. Cadmium inhibited the growth of tobacco seedlings, reduced thephysiological activity of tobacco seedlings and severely affected to carbon metabolism. Lowconcentrations of Cd can increase the dry weight of tobacco seedling root, and the nitrate reductaseactivity was also increased. Compared with the results of this study, we think if we want to havelow-hazard Tobacco in practice, we should control cadmium at the seedling stage of tobacco.5With the increase concentrations of cadmium, tobacco seedlings membrane permeabilityincreased, cell membrane permeability under10μmol/L Cd treatment has no significant differencecompared to control treatment, and under the100μmol/L and500μmol/L cadmium concentration,the cell membrane parade difference was not significant, it can be seen that the membrane has rupturedhappen, so, as to enhance cell membrane permeability changes in the concentration of cadmium littlechange. With increasing of cadmium concentration, the number of chloroplasts of mesophyll cells werereduced, chloroplasts size was changed to smaller, chloroplast grana layer structure was reduced. Themesophyll cell walls which appeared a large number of osmiophilic particles with increasingconcentrations of cadmium, this indicated that cell wall can deposite cadmium.6At the stage of seed germination, neutral environment is the best to seed germination, too acid ortoo alkaline will reduce the germination rate. Acidic environment conducive to tobacco seedgermination, the growth of seedlings and has beneficial to the accumulation of dry matter of tobacco. Asthe increased of pH, the dry weight of tobacco seedlings will be reduced. Each part of tobacco had ahigher cadmium content at the acidic environment, while the content decreased at the alkalineenvironment. Temperature could affect the cadmium content in tobacco. The low and high temperatureswould both reduce the cadmium content in tobacco. Tobacco had a max cadmium absorption at20℃condition. At low temperature and normal temperature conditions, the cadmium content of tobaccoshowed as: stem> root> leaf.While under high temperature conditions it presented as: root> leaf>stem. A small amount of Zinc could promote the growth of tobacco, but a large number of Zinc would have toxic effects on the growth of tobacco. There was competition and synergies between the of zincand cadmium. Cadmium absorption by tobacco was regulated by the zinc. zinc had a regulatory role inthe low zinc concentrations，but at high zinc concentration, zinc was more toxicity than cadmium,cadmium bind to the sites which bind zinc before, so the cadmium content of tobacco was increased.