Characteristics Of Cd Uptake And Distribution And Transcriptome Analysis In Two Cultivars Of Solanum Nigrum L.

Phytoremediation is a remediation technology for heavy metal contaminated soil that has received widespread attention.Understanding the uptake characteristics of hyperaccumulator can help improve remediation the efficiency of phytoremediation.There were few studies on Cd uptake mechanism of Solanum nigrum L.In this study,we used the S.nigrum L.and Solanum photeinocarpum as research materials to explore the uptake and distribution characteristics and to explore the mechanism of Cd uptake and distribution combined with transcriptome analysis.This study provided a theoretical basis for improving the remediation efficiency of S.nigrum L.The Cd uptake characteristics of the two cultivars of S.nigrum L.are significantly different:（1）The Cd content in above-ground and root of S.nigrum L.were both higher than S.photeinocarpum.The Cd content in the xylem sap of S.nigrum L.was higher than S.photeinocarpum.（2）The Cd content in symplast sap was higer than apoplast sap in two cultivars of S.nigrum L.（3）The absorption kinetics of Cd concentration of the two types of S.nigrum L.were in accordance with the Michaelis-Menten equation.The maximum Cd absorption rate of S.nigrum L.was higer than that of S.photeinocarpum.The flow rate of Cd in the roots of Solanum nigrum L.was 4.09 times that of S.photeinocarpum.There was no difference in the distribution and chemical forms of Cd between the two cultivars of S.nigrum L.The Cd chemical forms was mainly NaCl extraction,ethanol extraction and watersoluble extraction in above-ground.The Cd chemical forms was mainly HAC extraction in root.The pathway of Cd absorption and transport in Solanum nigrum L.was further studied.The results showed that spraying transpiration inhibitor had no directly essential effect on the absorption and accumulation of Cd in Solanum nigrum L.and Solanum photeinocarpum.Low temperature treatment（4℃）significantly reduced the absorption and translocation of Cd in Solanum nigrum L..the Cd concentration of shoot in S.nigrum L.and S.photeinocarpum decreased by 58.11%,33.15%respectively.At Cd level of 25 μM,the Cd concentration was 4-5 fold higher in xylem sap of S.nigrum L,as compared with that in external Hoagland nutrient solution,whereas 3-4 fold higher in xylem sap of S.photeinocarpum.The addition of the metabolic inhibitor,cyanide m-chlorophenythydrazone（CCCP）,significantly reduced the Cd concentration in xylem sap of S.nigrum L.,and the S.nigrum L.was more severely inhibited than S.photeinocarpum.The Cd concentration decreased by 50.07%,60.17%and 40.87%respectively in xylem sap,shoot and root of S.nigrum L.,compared with 40.12%,53.16%and 33.28%in xylem sap,shoot and root of S.photeinocarpum.These results indicate that Cd absorption and translocation is an active process in S.nigrum L.,symplastic pathway rather than apoplastic pathway plays a major role in the process of absorption,translocation and xylem loading.In order to clarify the absorption and accumulation mechanism of Cd in S.nigrum L.,We performed transcriptome sequencing and analysis of S.nigrum L.and S.photeinocarpum.Transcriptome differential expression analysis showed that under the treatment of 25 μM Cd,there were 2209 and 4760 significantly differently expressed genes respectively in S.nigrum L.and S.photeinocarpum.According to the analysis of Go enrichment of differential genes,the results showed that the catalytic,metabolic,and transport-related functions were significantly enriched,which may be involved in the Cd absorption and accumulation process of S.nigrum L.Through KEGG enrichment analysis,the glutathione metabolic pathway is involved in the Cd absorption and accumulation process of S.nigrum L.Further analysis revealed that the glutathione transferase gene,ZIP5 and MATE family DXT genes were significantly up-regulated in two cultivars of Solanum nigrum L.,indicating that the glutathione transferase gene,ZIP5 and MATE family DXT genes are involved in Cd absorption and accumulation in S.nigrum L.These findings provide a theoretical basis for improving the remediation efficiency of S.nigrum L.