Studys On The Genotypic Difference Of Cadmium Accumulation, Physiological Response And Methylated Change In Radish (Rapanus Sativus L.) Under Cadmium Stress

Radish (Raphanus sativus L.) is a very important world vegetable originated from china,it has been widely cultivated in china, its production area stands second in vegetable crops.With the development of mining, smelting industry and sludge dumping, sewage irrigatingin agiculture and using of phosphorus fertilizer, the problem of environmental pollutionwith cadmium is becoming increasingly urgent. Cadmium(Cd) is one of five most toxicheavy metals to plants, animals and the people, Cd pollution on vegetables was a importantproblem reducing the quality of vegetable production and damaging people health. How tocontrol and alleviate Cd-contaminated vegetables is urgently important. Most studiesshowed that Cd accumulation and tolerance within plant species have obvious geneticvariation. Consequently, It is one of best-effective and efficient approaches to choose andstudy varieties or genotypes of crop with low Cd accumulation in edible parts so as to makefull use of natural resources and guarantee food satefy. In this study, hydroponic cultureexperiments were conducted to study the physiological response and the DNA methylationlevel in Cd-tolerant genotype exposed to different Cd concentrations, based on the researchof the genotypic difference in Cd uptake in 46 radish accessions from different countries orregions. The results were summarized as follows:1. The study on genotypie differences of Cd absorption in Raphanus sativus cultivarsunder Cd stress46 radish (Raphanus sativus L.) cultivars were planted in the hydroponic system tostudy their differences in cadmium (Cd) uptake at seedling stage .The result showed thatthese radish cultivars had significant difference in absorption of Cd when plants weretreated with Cd²⁺ at 50 mg/L. The Cd content in root varied from 433.1 ug/g to 2838.4ug/g,while the Cd content in shoot was in a range of 136.4 ug/g to 521.1ug/g. Root exceed shoot.The radish Cd concentrations were significantly different: lowest in Nau-CW20, Nau-Hm-05-1 and RADISH-US, while highest in Nau-Brz, Nau-Bysj and Nau-Rg. The Cdcontent of root negative correlated significantly with the root dry weight and the shoot dryweight.2. Cadmium uptake character and stress effect on the growth and antioxidantenzymes activities in Raphanus sativusThe effect of cadmium (Cd) on germination rate, accumulation, and antioxidativeresponse was studied in Nau-Hm-05-1 radish seedlings. The seedlings were treated with thedifferent concentrations of Cd (0-500mg/L) in the hydroponic system.The rate ofgermination and seedling growth were markedly inhibited with the increasing concentrationof Cd²⁺. A concentration of 500 mg/L Cd²⁺ inhibited seedling emergency by 8ï¼…. Cdconcentration in roots and shoots of plants increased with the increasing concentration ofCd in the nutrient solution. The content of Cd in shoots and roots were about 20 and 25times than that of the control from the treatment of 500 mg/L Cd, respectively. The Cd²⁺stress could result in lipid peroxidation and induced an obvious increase in MDA content.The effect of Cd stress on the membrane protection enzyme system was evaluated and theactivity of CAT increased with the treatment of 0 to 250 mg/L Cd and then decreased withthe higher concentration of Cd; however, the activity of SOD and POD significantlydecreased with increasing concentration of Cd in the nutrient solution.3. Analysis of Genomie DNA Methylation Level in Radish under Cadmium Stress byMethylation-sensitive Amplified Polymorphism TechniqueThe level of cytosine methylation induced by cadmium in Nau-CW20 radish (Raphanussativus L.) genome was analysed using the technique of methylation-sensitive amplifiedpolymorphism (MSAP). The MSAP ratios in radish seedling exposed to cadmium chlorideat the concentration of 50, 250 and 500 mg/L were 37ï¼…,43ï¼…and 51ï¼…, respectively, andthe control was 34ï¼…; the full methylation levels (CmCGG in double strands) were at 23ï¼…,25ï¼…and 27ï¼…, respectively, while the control was 22ï¼…. The level of increase in MSAP andfull methylation indicated that de novo methylation occurred in some 5'-CCGG sites underCd stress. There was significant positive correlation between increase of total DNAmethylation level and CdCl₂ concentration. Four types of MSAP patterns: de novomethylation, de-methylation, atypical pattern and no changes of methylation pattern wereidentified among CdCl₂ treatments and the control. DNA methylation alteration in plantstreated with CdCl₂ was mainly through de novo methylation.