Effects Of Heavy Metal Cadmium On Antioxidant System Activity And Glyoxalase System Activity In Salix Matsudana Koidz.

Cadmium（Cd）is one of the serious contaminants in soil heavy metal pollution in China,which has attracted wide attention because of its high toxicity.Cd is easily absorbed and accumulated in plants,which has a toxic effect on the metabolic process of plants,and can also enter the food chain and pose a health threat to organisms.The antioxidant system and glyoxalase system in plants work together to maintain the homeostasis of reactive oxygen species（ROS）and methylglyoxaldehyde（MG）in cells,which plays an important role in the response and adaptation of plants to abiotic stress.Salix matsudana Koidz.is the main tree species used in urban greening in northern China,and has high tolerance to cadmium.In order to explore the effects of long-term cadmium treatment on physiology and related stress resistance gene expression of Salix matsudana Koidz.,this experiment took one-year Salix matsudana Koidz.plants as experimental materials and set CK（control）,25 mg·kg^-1,50 mg·kg^-1,75 mg·kg^-1 and 100 mg·kg^-1 cadmium treatment concentrations.Samples were collected at 10 d,20 d,30 d and 40 d after treatment,and were token at the same time in the second year.By analyzing the physiological indexes of antioxidant system and glyoxalase system as well as the expression of related stress resistance genes under cadmium treatment,the response of Salix matsudana Koidz.to different concentrations of cadmium treatment was studied,which provided some reference for clarifying the physiological mechanism of plant response to cadmium stress and the remediation of soil cadmium pollution.The results showed that:1.At the beginning of the first year of cadmium treatment,ROS level and antioxidant enzyme activity in Salix matsudana Koidz.leaves increased,and oxidative stress response in Salix matsudana Koidz.plants was enhanced.With the prolongation of treatment time,ROS level decreased,antioxidant enzyme activity increased in different degrees,and the activity of As A-GSH circulatory enzyme increased significantly,indicating that the adaptability of Salix matsudana Koidz.to cadmium was improved.Low concentration of Cd(25 mg·kg^-1,50 mg·kg^-1)was less harmful to Salix matsudana Koidz.,Salix matsudana Koidz.had higher adaptability.High concentration of cadmium(75 mg·kg^-1,100 mg·kg^-1)caused serious damage to Salix matsudana Koidz..Under the condition of cadmium treatment,Salix matsudana Koidz.could reduce the oxidative stress of Cd by increasing the activities of related antioxidant enzymes SOD,CAT and As A-GSH.2.The enzyme activities of Gly I and Gly II increased under different concentrations of Cd,while the accumulation of MG decreased.The detoxification of MG was accomplished by increasing the enzyme activity of Glyoxalase system.In each period of the second year,compared with the first year,the increase of MG content in the leaves of Salix matsumoides treated with different concentrations of Cd was smaller than that in the control group,indicating that the adaptability of Salix matsumoides to Cd was enhanced with the extension of time.3.In each period of the first year,under different concentrations of cadmium,the relative expression levels of SOD,CAT,APX,GR genes and chelating genes PCS,MTs and ABCB in Salix matsudana Koidz.leaves were all up-regulated,indicating that Salix matsudana Koidz.can alleviate the damage caused by cadmium stress through the antioxidant system and chelating cooperation.The relative expressions of SOD,CAT and MT2B genes were up-regulated more obviously in the second year than in the first year,and the expressions of APX,GR and MT2A genes were at the same level in the second year and the first year,indicating that Salix matsudana Koidz.had certain adaptability under long-term cadmium treatment.In conclusion,cadmium treatment can lead to the accumulation of ROS and MG in Salix matsudana Koidz.leaves.The increase of antioxidant enzyme activity alleviated the oxidative stress induced by cadmium treatment,and the enzyme activity of glyoxalase system increased to remove excess MG.Under Cd treatment,Salix matsudana Koidz.can improve the tolerance to Cd by regulating genes related to antioxidant enzymes（SOD,CAT,APX,GR）,and genes involved in chelate formation（PCS,MTs）and transport（ABCB）.