Comparative Morphological And Physiological Responses And Differential Gene Discovery In Kenaf(Hibiscus Cannabinus L.) Under Cadmium Stress

Kenaf(Hibiscus cannabinus L.)is annual,dicotyledonous bast fiber crop.Kenaf belonged to genus Malvaceae.It has strong vitality,high tolerance and enrichment ability for heavy metals.It is considered as a potential important phytoremediation plant.In recent years,the area of heavy metal pollution in farmland soils in China has gradually increased,threatening the health of crops and humans.Until now,there are few studies on abiotic stress in kenaf.However,the molecular mechanism of kenaf response to Cd stress is still unclear.Recent study was conducted to elaborate the molecular response under cadmium stress for two Kenaf cultivars(Fuhong 991(FH)and Yunnan Yuanjiang(YN),about twenty days old kenaf seedling were treated with three levels(0,10,30 mg/kg of CdCl2)of Cadmium stress for one week.The agronomic traits,physiological indexes and root vigor of the seedlings under three concentrations of Cadmium stress were measured.The enrichment of Cd in the two ctivars under different treatments was determined,and transmission electron microscopy was used to observe the root and leaf ultrastructure cells of two cultivars treated with 0,10 mg/kg Cd2+.At the same time,the leave transcriptomes of two varieties under 0 and 10mg/kg Cd2+ treatment were conducted and analyzed.The main results were shown as below:(1)The effects of heavy metal Cd on two kenaf varieties of FH and YN were determined by measuring some agronomic traits of kenaf seedlings.The study found that Cd has a very toxic effect on kenaf,causing roots,stems and other tissues and organs growth was reduce,and leaves chlorosis,curling and even falling off was observed.Moreover,with the increase of Cd treatment,the relative inhibition rate of various agronomic traits of kenaf cultivar FH(FH)was significantly lowered than that of(YN).(2)After one week of stress,the activities of SOD,POD,CAT and MDA contents in leaves and root activity of both kenaf cultivars were measured under different levels of Cadmium stress.In the range of 30mg/kg,with the increase of Cd stress,SOD,MDA and root activity increased gradually,POD activity increased first and then decreased,CAT activity showed a downward trend,the trends of various indicators were very obvious.Under different concentrations of Cadmium stress the activities of SOD and POD in FH were significantly higher than those in YN.MDA contents,root activity and CAT activity were noted significantly lower in FH than YN.(3)After one week of stress,the Cd content in root,stem and leaves of two kenaf var:ieties under different treatments was determined.It was noted that the enrichment degree of heavy metal Cd by kenaf showed root>stem>leaf,and under the same treatment,The Cd content in roots,stems and leaves of FH was higher than YN,it was proposed that the enrichment ability to Cd of FH was higher than YN.In the range of 0-30mg/kg,the content of Cd in the kenaf roots of FH and YN increased gradually,and the content in the stems and leaves increased first and then decreased.The roots of these two varieties reached the maximum value at 30mg/kg,FH was 2836 mg/kg,YN was 2976 mg/kg;but the stem reached the maximum value at 10mg/kg,FH was 320 mg/kg,and YN was 278 mg/kg;and the leaves also reached a maximum at 10 mg/kg,FH was 119 mg/kg,and YN was 96 mg/kg.(4)In present experiment,the ultrastructure of roots and leaves cell of FH and YN treated one week was observed by transmission electron microscopy(TEM).According to the analysis,compared with the control,the root cell structure of FH and YN under 10mg/kg Cd2+ treatment was destroyed,the cell wall was thickened,the nuclear membrane was blurred,the chromatin color was light;and the leaf cells had the same situation,the chloroplast thylakoid membrane structure was loose or disappeared,and leakage of the internal dissolved matter was noticed.At the same time,obvious the kenaf leaves of the two varieties under the 10 mg/kg Cd2+,YN have more serious damage to the chloroplasts than FH,almost no obvious chloroplasts were found,that is,from the cytological level,YN was more sensitive to heavy metal Cd than FH under 10 mg/kg Cd2+treatment.(5)The leaves of FH and YN under the treatment of Cd and blank were used for the the transcriptome sequencing.A total of 199762 Transcripts and 105437 Unigenes were obtained.Compared with FHO,there are 2,219 differentially expressed genes in FH10,compared with YNO,there are 3,320 differentially expressed genes in YN10.Among them,there are 525 same genes were found in differentially expressed of these two varieties,and the number of genetic changes in YN varieties is more than YN,it was said that YN is more sensitive to heavy metal of Cd;GO enrichment analysis of common differential genes found that it is mainly enriched in"cell composition","antioxidant enzyme activity"and"zinc-iron binding transport"Functional aspects.At the same time,in the KEGG metabolic pathway,the mainly enriched in metabolic pathways such as the"carboxylic acid metabolic pathway",the"MAPK signaling pathway",the"amino acid metabolic pathway",and the"MAPK signaling pathway".(6)The CXE1,MTP4,ZIP2,MT,MT2,ERF2,ERF5 gene sequences were cloned.The overexpression vector of CXE1,MTP4,ZIP2,MT,MT2,ERF2 and ERP5 was successfully constructed by double enzyme digestion.The over-expression vector of the constructed CXE1 gene was successfully transferred into tobacco by using tobacco genetic transformation system and a batch of transgenic plants were obtained by molecular detection.