Study Of Mechanism For Cadmium Accumulation By Pectin In Tomato Cell Wall

Cadmium?Cd?has generally been considered as a heavy metal which is highly toxic to plants and animals without a beneficial biological function.When the Cd content exceeds the limit,it not only inhibits the growth of the plant,but also accumulates in crops and affects human health.Studies have shown that the cell wall plays a key role in the physiological process of plant resistance,however,the mechanism of resistance of the cell wall to toxicity and gene regulation are not exhaustive enough.On the basis of previous studies,the tomato plant was selected as a research subject.In this work,the binding sites on the cell wall of tomato and Cd were discussed,the correlation between the content of pectin,the activity of PME and the Cd content in the cell wall was analyzed.Meanwhile,the role of the LeQUA1 and LePME1 gene in the regulation of the anti-cadmium mechanism of tomatoes was studied.The main results are summarized as follows:In order to explore the mechanism of adsorption of the tomato cell wall to heavy metal Cd,the cell walls of the tomato organs were modified.The influence of the cell wall on the adsorption rate of Cd and the amount of adsorption before and after the modification was studied by adsorption experiments.With the increase of time,the adsorption rate was gradually reduced,and the increase in adsorption decreased accordingly.Around 480min,the adsorption capacity of the cell wall reached saturation,and the amount of saturated adsorption was about 1.00 mg.g^-1.Compared with the untreated group,esterification,methylation adjustment and pectin content regulation reduced the Cd concentration immobilized in the cell wall.It was indicated that the degree of esterification,the pectin content and its degree of methylation of the cell wall play a key role in the adsorption of Cd in tomatoes.Meanwhile,by using the Fourier transform infrared spectrum,the information about the functional groups of Cd adsorption sites in the tomato cell wall was characterized.The FTIR spectra revealed that the maximum intensity and position of the hydroxyl and carboxyl groups in the cell wall were modified to different degrees before and after stress with Cd.It has been found that pectin is one of the main parts of the binding of the cell wall at Cd²⁺.In addition,under stress conditions,the hydroxyl and carboxyl groups in the cell wall interact mainly with Cd²⁺,which is the main binding site.Tomato seedlings were treated with different levels of Cd-stressed.Cell wall,pectin and pectin metesterase?PME?were extracted in different tomato organs.To investigate the effects of different Cd stresses on pectin content and PME activity in different tomato organs.With the increase of concentration of Cd-stressed,Cd content in tomato seedling organs increased significantly.The distribution of Cd in various organs is root>stem>leaf,Cd concentration in the cell wall and pectin are root>stem>leaf.The experimental results showed that Cd concentration in the pectin accounted for about 12²7%of the cell wall,indicating that pectin is the main binding site for the accumulation of Cd in plant cell wall.Meanwhile,with the increase of the Cd-stressed concentration,the pectin content and the activity of PME also increased.Both the pectin content and the PME activity correlated positively with the Cd accumulation of the cell wall.Rt-PCR was used to study the regulation of the mechanism of Cd tomato accumulation by LeQUA1and LePME1.The results showed that,compared to CK,treatment with Cd for 12h,24h,the expression of the LeQUA1 gene decreased by 30.02%and increased by 158.08%,respectively.After 36h of Cd stress,the expression of the LeQUA1 gene was slightly down regulated.After treatment with Cd for 14 days,the expression of the LeQUA1 gene was significantly increased by 68.62%.In comparison with CK,the expression of the LePME1 gene was reduced by 54.83%when treated with Cd for 12h.When Cd-stressed with 24h and 36h,the expression of the Le PME1 gene changed little.After Cd-stressed for 14 days,the expression of the LePME1 gene increased by79.69%.In addition,the expression of different Cd stress times was compared.The expression of the LeQUA1 gene was positively regulated at 24h,36h and 14days under Cd stress,which were 3.69,1.30 and 2.41 times of 12h,respectively.Meanwhile,the expression of the LePME1 gene in 24h,36h and 14 days under Cd stress was also positively regulated,which were 2.37,1.91 and 3.98 times of12h,respectively.