Preliminary Study On The Tolerance Mechanisms Of Heavy Metal Cadmium In Halogeton Glomeratus

Heavy metal pollution of soil has become one of the major global environmental pollution problems.The excessive accumulation of heavy metal ions in soil not only destroys the structure of soil system,but also affects the growth and development of plants,and ultimately threatens human health by food chain.Therefore,making full use of land resources and carrying out economic and effective remediation of soil heavy metal pollution are of great significance for improving the ecological environment and ensuring the sustainable development of agriculture and human health.To explore the molecular mechanism of plant response to heavy metal stress is an important basis for the cultivation of new heavy metal tolerant plant varieties.Halophyte Halogeton glomeratus（H.glomeratus）,an annual herb of Chenopodiaceae,is an ideal wild resource for heavy metal contaminated soil remediation,which is not only a pioneer plant of drought and salt tolerance in Northwest China,but also a dominant population in metal mining area.However,the tolerance characteristics and molecular mechanism of H.glomeratus to heavy metal Cd have not been reported yet.In view of this,this study systematically studied the tolerance characteristics of H.glomeratus to Cd in different growth stages.Firstly,the seeds of H.glomeratus were treated with different concentrations of heavy metals（Cu,Zn,Ni,Cd and Pb）respectively to determine the tolerance to different heavy metals during germination.Secondly,the seedlings growing for 20 days were treated with different concentrations of Cd solution to analyze the physiological characteristics of response to Cd stress.Finally,the molecular mechanism of the response of H.glomeratus leaves to Cd stress was studied by proteomics.The main results are as follows:1.During the germination period,the H.glomeratus seeds were stressed with different concentrations of heavy metals（Cu,Zn,Ni,Cd and Pb）respectively,and the germination indexes and seedling growth indexes were measured and analyzed.It was found that the low concentration of heavy metals（Cu,Ni,Cd,Pb）had little effect on the germination of H.glomeratus seeds,while the high concentration had an inhibitory effect.In addition,different concentrations of Zn had no effect on the germination of H.glomeratus seeds.2.The clustering results show that there were little effects on seed germination and seedling growth of H.glomeratus while the heavy metal concentrations are lower than 3.00 mmol·L^-1 Zn,1.00 mmol·L^-1 Pb,Cu,Ni and 0.10 mmol·L^-1 Cd.The results of principal component analysis showed that The germination indexes can be used as an important parameter for evaluating the tolerance of H.glomeratus to Zn,Pb and Ni during the germination period,and biomass can be used as an important parameter for evaluating the tolerance of H.glomeratus to Cu and Cd in the germination period.3.The seedlings of H.glomeratus cultivated for 20 days were stressed with different concentration of Cd solution.After treatment,the growth morphology and physiological characteristics of the seedlings were analyzed.The results showed that H.glomeratus had a strong tolerance to heavy metal Cd,with the highest content of Cd²⁺in the root,the second in the leaves and the lowest in the stems.The concent of Cd²⁺in the leaves of H.glomeratus was 160 mg·kg^-11 and its transfer coefficient to Cd²⁺is 0.75 when the treatment concentration of Cd was 0.6 mmol·L^-1,indicating that H.glomeratus had a strong enrichment effect on Cd.In addition,the aboveground biomass of H.glomeratus was large,and about 15 times than of the underground,which endowed the H.glomeratus with the characteristics of enriching a large number of metal ions.4.DIA proteomics was performed to analysis the molecular characteristics of H.glomeratus leaf growing for one month,treated with 0.4 mmol·L^-11 Cd for 0,6,12,24h and 48 h,in response to heavy metal Cd stress.412,343,478 and 385 differentially expressed proteins（DEPs）were identified at 6,12,24 and 48 hours.Among them,566 DEPs were identified at 6,12 h and 669 DEPs were identified at 24,48 h,indicating that the longer the treatment time,the more DEPs were involved in response to Cd stress.5.189 proteins were co-expressed in the induction stage treated with Cd for 6,12h,which were mainly involved in translation,ribosome structure and biogenesis,energy production and conversion,and 194 proteins were co-expressed in the adaptation stage treated with Cd for 24,48 h,which were mainly involved in secondary metabolites biosynthesis,transport and catabolism,signal transduction mechanisms,amino acid transport and metabolism,intracellular trafficking,secretion,and vesicular transport.At the same time,there were 61 and 20 core up-regulated and down-regulated proteins respectively.which play an important role in the molecular mechanism of response to Cd stress.6.In this paper,we identified that the differential expressed proteins（DEPs）related to heavy metal Cd chelation were metallothionein,glutathione-S-transferase and S-adenosylmethionine synthetase.Meanwhile,we identified that the DEPs related to heavy metal Cd transport were ABC transporters（mainly ABCB1 and ABCC2families）,with subcellular localization on plasma membrane.These proteins may be involved in the detoxification process to Cd of H.glomeratus leaves.