Silicon-induced Reversibility Of Cadmium Toxicity And The Underlying Mechanisms In Poplar Plants

With the development of human activities and society and economy,the harm of soil cadmium?Cd?pollution to human health and ecological environment has been getting increasingly severe.In order to alleviate soil Cd pollution,the phytoremediation technology was proposed.Silicon?Si?,the second abundant element in the earth's crust only inferior to oxygen,is not only beneficial to the growth of higher plants,but has the ability to improve the resistance of plants to heavy metals,which may play an important role in the field of phytoremediation.In this study,Populus euramericana clone I-214 was used as the experimental object in a Hoagland nutrient hydroponic culture to examine the reversibility of Si to Cd toxicity in poplar plants,to explore the effect of exogenous Si on the changes of physiology and biochemistry and transicriptome,which may provide insights into the mechanism of Si in alleviating the toxicity of Cd to poplar plants.The main results of this study are as follows:1.The application of exogenous Si increased the growth of I-214 plants,increased the fresh weight and dry weight of the aboveground and belowground parts,increased plant height and root collar diameter,and reversed the decline of plant growth caused by Cd stress.2.After application of exogenous Si to the poplar plants stressed by Cd,the net photosynthetic rate and transpiration rate increased,the photosynthetic capacity improved,the stomatal conductance increased and the concentration of CO₂ decreased.Compared to the Cd stress treatment group,Cd+Si treatment reversed the decrease of chlorophyll content resulted from Cd toxicity.Chlorophyll a,chlorophyll b and carotenoid contents all increased,suggesting the reversal effect of Si on the toxicity of Cd.3.After application of exogenous Si to the poplar plants stressed by Cd,the contents of H₂O₂,O₂^-·and MDA effectively decreased,the activity of SOD and CAT significantly increased,the POD activity which reduced under Cd stress significantly increased,the content of soluble protein in the leaves of the plant significantly increased,the content of proline in the leaves of the plant reduced,and the root activity of the plant increased,demonstrating the reversal effect of Si on the toxicity of Cd.4.After application of exogenous Si to the poplar plants stressed by Cd,the Cd content of the plant reduced,the Mn content in leaves and roots and the Na content in leaves and stems effectively enhanced,but the content of Mg did not change,and the content of Ca,Fe,Mn,Cu and Zn in the root of the plant increased.5.The transcriptional analysis of Cd and CK treatment groups of clone I-214 showed that 954 differentially expressed genes?377 up-regulated genes,577 down-regulated genes?were identified,of which 722 genes were annotated to 1950 GO terms,and 62 genes were annotated to 80 KEGG pathways.The transcriptional analysis of Cd and Cd+Si treated groups revealed 366 differentially expressed genes?202 up-regulated genes and 164 down-regulated genes?.Among them,273 differential genes were annotated to 1325 GO terms,and 22 genes were annotated to 37 KEGG pathways.10 differentially expressed genes were randomly selected for real-time fluorescence quantitative PCR verification,the results were basically consistent with the results of the transcriptional sequencing.The accuracy of the sequencing results was further confirmed.