| Cadmium(Cd)is a heavy metal element with a long half-life that cannot be undecomposable,and it has the ability to be absorbed by plant roots and accumulated in the edible part of plants,where it can lead to its enrichment in the food chain,ultimately posing a threat to human health and causing various diseases.Silicon(Si)is the second abundant element in the earth’s crust after oxygen.Although it is a nonessential element,it has been found to have beneficial effects on plant growth and development.It has been shown that silicon can plant resistance to various adversities.Wheat is a crucial crop for over 35% of the global population and is the second largest food crop in China.The yield and quality of wheat have a direct impact on food security.This study focuses on winter wheat(Bainong 307)as the experimental material to investigate the response mechanism of wheat seedlings to varying concentrations of cadmium and explore the physiological,biochemical,and molecular mechanisms of exogenous silicon in mitigating cadmium toxicity in wheat under cadmium stress.The study provides both theoretical and practical foundations for the advancement of silicon-based fertilizers that can effectively control heavy metal toxicity in crops and promote food security.The following results were obtained from the study:1.Low concentrations of Cd(0.1-0.5 μM)did not significantly affect the growth of wheat seedlings to a certain extent,while high concentration of Cd(>10 μM)significantly inhibited the growth of wheat.High concentrations of Cd can be toxic to plant growth and development.It can reduce seedling height and root length,as well as the accumulation of biomass,and the reduction in photosynthetic pigments,such as chlorophyll a(Chla),chlorophyll b(Chlb)and total chlorophyll(TChl),and the inhibition of photosynthesis can occur through decreased photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO2 concentration(Ci),and transpiration rate(Tr).In addition,high levels of Cd can also trigger the generation of reactive oxygen species,leading to an increase in the content of malondialdehyde(MDA)in both shoots and roots.Under Cadmium stress,the antioxidative capacity of wheat seedlings was enhanced to eliminate excessive reactive oxygen species in the plants,which was mainly observed through an increase in the content of antioxidants and the activity of antioxidant enzymes.The contents of ascorbic acid(As A),glutathione(GSH),nonprotein thiol(NPT),and phytochelatin(PC)in both the shoot and the root were significantly increased,ranging from 5.45% to 545.01%,1462.03% to 8116.79%,176.46% to 1599.92%,and 140.75% to 1418.88% in root,respectively.Additionally,the content of As A in shoots was increased by 16.23% to 157.98%,that of GSH,NPT and PC were increased by 6.07% to 28.11%,0.69% to 49.39% and 4.08% to 73.11%,respectively.The activities of superoxide dismutase(SOD),ascorbate peroxidase(APX),and peroxidase(POD)in shoots,and catalase(CAT)and APX in roots were also enhanced,ranging from 2.92% to 24.28%,4.74% to 36.78%,36.72% to 90.44%,1.78% to 205.91%,and 6.82% to 352.82%,respectively.2.In the presence of Cd stress(10 μM),the growth of wheat was considerably impeded when compared to the control group(CK).However,with the addition of exogenous Si(1 m M,Cd Si),the growth of wheat was enhanced significantly,and the toxicity of Cd on wheat seedlings was effectively relieved.The addition of exogenous silicon promoted root development,as well as root and shoot growth,resulting in increased biomass accumulation and improved cadmium tolerance of wheat.Furthermore,the utilization of Si was observed to reduce the concentration of Cd in both aboveground and underground parts of wheat seedlings by 70.34% and 67.45%,respectively.Additionally,Si was found to support the uptake of mineral elements in wheat and elevate the levels of Mg,Na,and Mn in the underground part.Analyzing the weight network of chemical elements,there was a notable adverse relationship between the levels of Mg,Mn,Na and the Cd concentrations in roots,implying that Si could enhance the intake of Mg,Mn and Na while reducing Cd absorption.3.Under the influence of Cd stress(10 μM),wheat seedlings experienced significant oxidative damage.However,with the implementation of Si application,the photosynthetic performance and the ability for chlorophyll synthesis increased considerably,resulting in a 5.41%,69.82%,27.17% and 47.01% improvement respectively for parameters like Pn,Gs,Ci,and Tr.The contents of Chla,Chlb and TChl also saw an increase by 24.37%,72.58% and 29.42%,correspondingly.Through exogenous Si addition,oxidative harm caused by Cd was effectively alleviated,as seen in the reduction of MDA content in the shoot and root by 46.62% and 75.09%respectively.Si was additionally observed to remove free radicals by enhancing the potency of antioxidant enzymes.The activities of SOD and CAT in leaves and SOD and APX in roots notably increased by 224.56%,125.18%,137.50%,and 145.54%respectively.Furthermore,Si usage resulted in a substantial rise in GSH,NPT,and PC levels in wheat leaves by 16.20%,11.36%,and 10.72% respectively,thus lowering the oxidative destruction of leaf cells caused by Cd.4.In comparison to the control group(CK),Cd stress caused a significant downregulation of 2781 genes in leaves and 3444 genes in roots,while up-regulating 3284 genes in leaves and 3916 genes in roots.Under Cd stress,Si application led to the downregulation of 3049 genes in leaves and 2071 genes in roots with an up-regulation of5179 genes in leaves and 3092 genes in roots.A Venn analysis demonstrated that there were 2086 common genes in leaves and 2173 common genes in roots among different treatment groups(CK,Cd,and Cd Si).The differential expression genes were subjected to Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)enrichment analyses.GO enrichment showed a significant enrichment in nicotianamine synthesis and metabolic processes in roots(CKR vs Cd R,Cd R vs Cd Si R),while KEGG enrichment demonstrated a significant enrichment in phenylpropanoid biosynthesis pathway,glutathione metabolism pathway,and starch and sucrose metabolism pathway(CKL vs Cd L,Cd L vs Cd Si L,CKR vs Cd R,Cd R vs Cd Si R).Additionally,the plant hormone signal transduction pathway was enriched in leaves.Weighted gene coexpression network analysis(WGCNA)indicated that 11 modules in leaves and 21 modules in roots were closely related to wheat seedlings traits.MEred and MEturquoise in leaves,and MEblue,MEyellow,MEgreen,and MEturquoise in roots were significantly correlated with Cd concentrations in shoot or root,respectively.GO and KEGG enrichment analysis pointed out that cell wall,redox reaction processes,the glutathione metabolism pathway,ABC transporters,phenylpropanoid metabolism pathway,and starch and sucrose metabolism pathway were also significantly enriched.The hub genes of the module were identified,and genes encoding heavy metal-related isoprenoid plant protein(HIPP)(LOC123125426,LOC123055069)were found to play a vital role in regulating cadmium transport and detoxification.Finally,the results obtained through q RT-PCR agreed with those of transcriptome sequencing.The findings from this investigation indicate that Si primarily activates transcription factors via signal transduction pathways,which in turn regulates the expression of downstream crucial genes of photosynthesis,antioxidant systems,and transporters.This leads to a reduction in Cd absorption and an enhancement of the antioxidant system’s ability,ultimately mitigating the toxicity of Cd and improving the tolerance of wheat seedlings. |
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