| In recent years,the area of soil salinization increased year by year due to unreasonable tillage managements,over-developed farming,and global climate changes.However,a large percentage of salt-effected soil is simultaneously contaminated with heavy metals.Salinity could enhance the mobility of heavy metals in soil and increased accumulation of heavy metals in plants,which would pose great threat to crop growth and food safety.Aside from increased the mobility of soil heavy metals induced by salinity,the impact of the regulation of plant response to salt stress on soil heavy metal mobilization and them uptake in plant.Thus,two contrasting Cd-accumulator edible amaranth(Amaranthus mangostanus L.)cultivar,names Liuye(high-Cd accumulator)and Quanhong(low-Cd accumulator),that screened by previous study are chosen for this study.Metabolomics and transcriptomics were used to investigate metabolic adjustment of edible amaranth cultivar in response to salt stress.We aimed to reveal the effects of metabolic adjustment on the mobility of soil heavy metals and them uptake in edible amaranth cultivar.The main results and conclusions were listed as below:(1)To investigate the impact of edible amaranth cultivar on the mobility of heavy metal in soil,and them uptake and accumulation in plant,two edible amaranth cultivars,Liuye and Quanhong cultivar,were subjected to salinity treatment both by soil culture and hydroponic culture,respectively.The results showed that salinity significantly promoted Cd accumulation in roots and shoots of edible amaranth cultivar in soil culture,however,Cd accumulation in roots and shoots of edible amaranth cultivar was inhibited by salinity in hydroponic culture,especially for Liuye cultivar.The total mobilized Cd amount in rhizosphere under salinity treatment increased 1.78 in Quanhong cultivar and 3.36 in Liuye cultivar compared with controls,in which 51.2% in Quanhong cultivar and 80.5% in Liuye cultivar was contributed by biological mobilization induced salinity.Therefore,we deduced the biological mobilized induced by salinity played an important role in enhancing the mobility of soil heavy metal under salt stress treatment,and the increased the mobility of heavy metals in soil played major contribution to the increased Cd accumulation in edible amaranth cultivar.Furthermore,more Cd accumulation in Liuye cultivar than Quanhong cultivar was resulted by a stronger ability in mobilised soil Cd in in Liuye cultivar.(2)The metabolites in root and leaf of edible amaranth cultivar,and metabolite in rhizosphere were extracted and identified by gas chromatography mass spectrometry technology.The corresponding standard were purchased and identified in the same condition,eventually the spectrum library of the metabolites in edible amaranth cultivar were established.According to the spectrum library of the metabolites in edible amaranth cultivar,metabolite in roots,leaves and rhizosphere both in control and salt stress treatment in soil culture were identified.Furthermore,the root exudates of edible amaranth cultivar in hydroponic culture were also identified.Multivariate statistical analysis showed that metabolic profilings in root,leaf,rhizosphere soil,and root exudates all showed significantly different between control and salt stress treatment.Among the metabolites identified in rhizosphere,the metabolites have strong ability in mobilise soil Cd,such as oxalic acid,malic acid,fumaric acid,glyceric acid,threonic acid,3-hydroxybutyric acid,aspartic acid and glutamic acid,their levels were showed significantly increased under salt stress treatment compared with the control,and it played a major role in enhancing effect of biological mobilized by salinity.The increased accumulation of organic acid in rhizosphere under salt stress treatment was mainly resulted by the increased secretion of organic acid from the root of edible amaranth cultivar.The up-regulated TCA cycle(tricarboxylic acid cycle)was an important response mechanism for edible amaranth cultivar to cope with salt stress.Furthermore,the increased level of glucose,fructose,ribose,glycerol,inositol,serine and 4-aminobutyric acid played a major role to adapt to salt stress treatment for Liuye cultivar,and the increased level of ribose and increased synthesis of proline were major mechanism to adapt to salt stress for Quanhong cultivar.(3)A high quality and homogeneous c DNA library was constructed by DSN(Duplex-Specific Nuclease)nuclease,and then the homogeneous c DNA library was sequenced with high throughput sequencing and de novo assembly.A total of 22.3 Gb data about transcriptomics of edible amaranth were obtained.A total of 104483 Unigene was obtained after assembled by de novo and removal of redundancy,the mean length,N50 and GC ratio of Unigene were 921 bp,1661 bp and 4084%,respectively.All Unigene were blasted to 7 of functional database and annotated.A total of 69234 Unigene were annotated,the annotation ratio is 66.26%.Furthermore,a total of 60486 sequence coding for aminoacids in protein(CDS)were detected,and the 9584 CDS was obtained using the ESTScan prediction.At the same time,9961 simple sequence repeats spread over in 8550 Unigene were detected.A total of 1816 transcription factor were predicted,which distributed in 57 transcription factor family.These results provide important reference genome information for subsequent research on edible amaranth cultivar.(4)According to the obtained transcriptome reference genome information of edible amaranth cultivar,digital gene expression profile of root of edible amaranth cultivar under control and under salt stress were sequenced and analyzed.A total of 5593 significantly differentially expressed genes(DEGs)for Liuye cultivar and 1052 DEGs for Quanhong cultivar were identified between control and salt stress treatment,respectively.These results indicated that Liuye cultivar might be more sensitive to salt stress compared with Quanghong amaranth cultivar.Salt stress up-regulated the expression level of aluminum activated malate transporter(ALMT).Thus,it can be deduced that the up-regulated expression level of ALMT triggered by salt stress promote secretion of malic acid from root to rhizosphere,which played an important role in rhizosphere soil acidification and the increase Cd biological mobilization under salinity stress.The genes belong to pectinesterase,polygalacturonase and GAUT were down-regulated by salt stress in the root of Liuye cultivar,which might result in a decrease content of pectin and Methxyl-esterification of cell wall of root.The decrease content of pectin and Methxyl-esterification of cell wall of root might lower ability of Cd adsoption and interception by root resulted in more Cd go through cell wall into protoplast.However,the genes belong to cell wall were not showed any significant change for Quanhong cultivar under salt stress treatment.The result means that salt stress did little effect on the cell wall of root in Quanhong cultivar.The genes belong to Nramp5,ZIP2 and HMA2 were down-regulated by salt stress treatment,which meaned that Cd adsorb onto root might be inhibited.The ABCC3 were up-regulated by salt stress treatment,which might promote Cd transport into vacuole and promote Cd detoxic ability of edible amaranth cultivar.Above all,we deduced that the incrased Cd accumulation in edible amaranth cultivar under salt stress treatment might not be induced by the change of Cd adsorb ability of root,but might be contributed to an increase Cd mobility in soil,the decrease Cd adsorption by cell wall and increased ability of Cd vacuole compartmentation.Furthermore,some genes involed in cation transport,such as CAX3,ZIP6,MTP10,HMA5,and OPT4,were also signficantly differentially expressed.Eventhough there are not any relevant research has shows their either taking part in Cd adsorb and transport,but they might be important candidated genes to influence heavy metals accumumulation in plant. |
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