Study On The Effect Of Exogenous DMTU On Two Tall Fescue Varieties With Different Tolerance Under Cadmium Stress

Under cadmium（Cd）stress,the physiological metabolism of tall fescue（Festuca arundinacea）is affected.Plants respond to adversity stress through phenotypic changes.The ability of plants to resist heavy metal Cd stress is closely related to the interaction between indole-3-acetic acid（IAA）and hydrogen peroxide（H₂O₂）in plants.N,N’-Dimethylthiourea（DMTU）,as a reactive oxygen species（ROS）scavenger,can effectively alleviate the toxic effects of Cd on plants by affecting the distribution and transportation of IAA.In this study,two varieties of tall fescue,Cd-resistant variety‘Arid 3’and Cd-sensitive variety‘Crossfire III’were used as test materials.The two cultivars were treated with Cd,DMTU and Cd+DMTU by hydroponics to explore the differences of growth morphology,physiological indexes and antioxidant system of two Cd tolerant varieties in response to DMTU under Cd stress.The main results are as follows:（1）Under Cd stress,the cell membrane permeability,MDA and H₂O₂ contents of each part of the two cultivars increased.The level of IAA in roots decreased while the activity of IAA oxidase increased.The level of IAA in leaf tip increased while the activity of IAA oxidase decreased.These led to electrolyte leakage,membrane lipid peroxidation,ROS production and affected distribution and transportation of IAA,which resulted in the oxidative degradation of IAA and the blocking of polar transport.Eventually,the height of tall fescue and the growth of primary roots are inhibited,the number of lateral roots and root hair increased,and the death rate of root tip cells increased,too.At the same time,the plant’s own antioxidant defense system plays a role.The glutathione（GSH）content and the four antioxidant enzyme activities of ascorbate peroxidase（APX）,catalase（CAT）,peroxidase（POD）and superoxide dismutase（SOD）increased.（2）Under Cd stress,DMTU could alleviate the increase in membrane permeability,contents of MDA and H₂O₂.It also,could increase IAA level in root and decrease IAA oxidase activity.It partially decreased IAA level in leaf tip.In turn,it alleviated electrolyte leakage,cell membrane lipid peroxidation and ROS levels caused by Cd stress,inhibited the oxidative degradation of IAA,and promoted its transport to roots.So as to alleviate the inhibition of Cd stress on tall fescue plant height and primary root elongation,reduce the formation of lateral roots and the death rate of root tip cells.At the same time,the plant’s own antioxidant defense system recovered to a certain extent.The content of GSH and the four antioxidant enzyme activities of APX,CAT,POD and SOD were reduced.（3）There are certain differences in the tolerance mechanisms of different varieties of tall fescue.In this study,compared the changes in growth morphology,physiological indicators,antioxidant systems and other aspects of two different tolerant tall fescue varieties.It was found that under Cd stress,exogenous DMTU had a more significant alleviating effects on the number of lateral roots,primary root length,root tip cell death rate,cell membrane permeability,H₂O₂ content,IAA content,and IAA oxidase activity of‘Crossfire III’,and a more significant mitigation effect on the plant height of‘Arid 3’.On the whole,the mitigation effect of DMTU on the Cd-sensitive variety‘Crossfire III’is better than that of the Cd-resistant variety‘Arid 3’.（4）Through the comparison group of Cd+DMTU vs Cd,various indexes of growth morphology,physiological indexes and antioxidant system were studied,and the change range of each index between different parts of two kinds of tall fescue was compared.It is found that DMTU has a stronger degree of mitigation to roots than the stem and leaf tip.