Cadmium Tolerance Mechanism Of Populus’ Zhonghua Hongye’

Environmental pollution especially soil heavy metal cadmium pollution,is a global problem.Phytoremediation technology uses plants to absorb heavy metals in soil and remove them in the easy-to-harvest part of the ground.This technology is both green and environmentally friendly.Woody plants have the advantages of large biomass,wide root expansion depth and range,high nutrient and water uptake efficiency,and low management costs.Woody plants can make use of their high biomass to compensate for low transport efficiency,and rely on their genetic diversity to enhance phytoremediation effect.Populus’Zhonghua Hongye’is a new variety successfully cultivated through the bud variety of fast-growing poplar-2025（ZL-2025）.It not only has the characteristics of strong growth capacity and quick adaptability,but also has the advantages of long colorful red leaves,bright color and no male catkin.Populus’Zhonghua Hongye’and ZL-2025 were treated with 50μmol·L^-1 Cd Cl₂ for15 days.The physiological changes of Populus‘Zhonghua Hongye’under cadmium stress were as follows:Natural root growth was inhibited;after 15 days of cadmium treatment,the root activity measured by TTC method was still 11.68U·g^-1FW.Chlorophyll content of poplar leaves decreased.The anthocyanin content in leaves of Populus auriculata was significantly increased.The anthocyanin content in leaves of populus auriculata was 18.2nmol·L^-1 by ethanol extraction with hydrochloric acid under natural growth condition,which was much higher than that in ZL-2025(7.6nmol·L^-1).After cadmium treatment,anthocyanin content in POPULus auriculata was further increased.At 15 days,the anthocyanin content in all treatment groups reached31.2 nmol·L-1,nearly twice that of CK group.ROS was formed in the roots and leaves of Populus chinensis.The content of MDA in the products of membrane lipid peroxidation increased,and after 15 days of cadmium treatment,the content of MDA in the leaves of Populus‘Zhonghua Hongye’was significantly lower than that of ZL-2025.After cadmium treatment,the antioxidant enzyme activity of Populus‘Zhonghua Hongye’was significantly enhanced.When Populus‘Zhonghua Hongye’accumulated more cadmium,the increment of ROS and MDA was not higher than that of ZL-2025,and the antioxidant enzyme activity of Populus‘Zhonghua Hongye’root was stronger than that of ZL-2025.Respectively,after cadmium treatment cadmium accumulation of the whole plant was 0.98mg and 0.83mg.The cadmium accumulation of the Populus‘Zhonghua Hongye’was also higher than that of the ZL-2025.The transport coefficients of S/R and L/R were 42 and 23 respectively.The total cadmium accumulation in aboveground was higher than that in ZL-2025.Transcriptome sequencing analysis revealed that a large number of differentially expressed genes were found after 10 days of 50μM cadmium stress.Compared with the control group,2205 genes were up-regulated in the roots and 1342 genes were up-regulated in the leaves of Populus’Zhonghua Hongye’.The GO enrichment analysis of Populus’Zhonghua Hongye’showed that the differentially expressed genes were significantly enriched in the biological processes of regulating transcription,protein phosphorylation,oxidation-reduction process,response signal transduction to cadmium ions and defense response when subjected to heavy metal cadmium stress.After cadmium stress,the genes related to oxidation-reduction process were up-regulated in two kinds of poplars.The physiological data showed that ROS,antioxidant enzymes and phenolic compounds（anthocyanins）values were increased.Transcriptome analysis showed that the genes related to defense response and response to cadmium ions were up-regulated.The strong cadmium absorption capacity of Populus’Zhonghua Hongye’is accompanied by strong physiological and molecular detoxification ability to effectively protect itself from toxicity.