Effects Of Cadmium Stress On Pectin And Lignin Synthesis In Roots Of Brassica Juncea

Soil cadmium(Cd)contamination is a serious environmental problem worldwide.Phytoremediation is one of the most promising approaches to the remediation of heavy metal-contaminated soils.Brassica juncea can be enriched with a variety of heavy metals,so it has the potential to be used in phytoremediation of soil heavy metal pollution.Therefore,it is of great significance to study the absorption mechanism of Cd.The cell wall is the first barrier for heavy metals in soil to enter plant root cells.However,the effect of Cd stress on the cell wall of root cells in B.juncea is currently unclear.This thesis explores the effects of Cd stress on lignin and pectin synthesis in cell walls of Brassica juncea roots.This study is to reveal the mechanism of Cd accumulation in mustard and provide references for breeding mustard varieties suitable for phytoremediation.The results of the study are as follows:(1)The contents of lignin and pectin and related enzymes(phenylalanine ammonia-lyase,laccase,superoxide dismutase,peroxidase,and pectin esterase,etc.)were determined in B.juncea roots treated with 80 μmol/L CdCl2 for 0 h,48 h,and 7 d).The results showed that the content of lignin and pectin in the cell wall of roots increased after Cd stress.The activities of phenylalanine ammonia-lyase,laccase,superoxide dismutase,and peroxidase increased with the increase of stress time.In contrast,the activity of pectin esterase decreased with the increase of stress time.(2)The effects of Cd stress at different times(0 h,48 h,and 7 d)on roots lignin and pectin synthesis related metabolites in B.juncea seedlings were analyzed by liquid chromatography-mass spectrometry(LC-MS).The results showed that Cd stress had a significant effect on the levels of lignin and pectin synthesis-related metabolites in the cell wall of B.juncea roots,and the differential metabolites of the phenylpropane metabolic synthesis pathway were significantly upregulated.The contents of three types of lignin monomers increased,and the synthesis ability of cell wall lignin was enhanced.The differential metabolites enriched in the galactose metabolic pathway were significantly upregulated,the contents of oligosaccharide and polysaccharide substances in cells increased,and the ability to polymerize into pectin was enhanced.(3)Transcriptome high-throughput sequencing was used to detect the differentially expressed genes of B.juncea roots under Cd stress at different times(0 h and 7 d),and the detected differentially expressed genes(DEGs)were functionally annotated and enriched by GO database and KEGG database.The results showed that a total of 2725 DEGs and 115 enrichment pathways were identified.Under Cd stress,the DEGs in B.juncea roots were mainly expressed down-regulated,indicating that B.juncea roots mainly responded to Cd stress through negative regulation of genes.In the phenylpropane metabolism synthesis pathway,94 DEGs were identified,and the proteins encoded mainly included phenylalanine ammonia-lyase,laccase,peroxidase,cinnamate-4-hydroxylase,and coumaric acid-3-Hydroxylase and 4-coumaric acid coenzyme A ligase.In the galactose metabolic pathway,10 DEGs were identified,of which 7 gene expression was upregulated and 3 gene expression was down-regulated,these genes were identified proteins encoding glucosidase,galactotransferase,and glucose isomerase promoted the synthesis of polysaccharides such as raffinoidase,mannose,medise,inositol,sucrose,and galactitol,and induced the increase of cell pectin content.