Studys On The Genotypic Difference Of Lead Accumulation, Physiological And Genetic Mechanism In Radish (Rapanus Sativus L.) Under Lead Stress

With the development of mining, smelting industry and using of all kinds of fertilizer, the problem of environmental pollution with Lead is becoming increasingly serious. Lead (Pb) is one of most toxic heavy metals to plants, animals and the people, whose pollution on vegetables was an important problem reducing the quality of vegetable production and damaging to people health. Choosing genotypes of crops with low Pb accumulation in edible parts is one of best-effective and efficient approaches to make full use of natural resources and guarantee food satefy. Radish (Raphanus sativus L.), originated from china, is an important world vegetable. In this study, hydroponic culture experiments were conducted to study the differences in Pb accumulation among radish genotypes, the genetic models of Pb accumulation, the physiological response and the DNA methylation level of radish to Pb stress. The results were summarized as follows,1. The Study on Genotypic Differences of Pb Absorption in Raphanus sativus CultivarsEight radish (Raphanus sativus L.) cultivars were planted in the hydroponic system to study their differences in Pb uptake. The results showed that these radish cultivars had significant difference in absorption of Pb when plants were treated with different pb concentrations .The Pb concentrations in root varied from 0.67 to 14511.86mg/kg, while the Pb concentrations in shoot was in a range of 0.13 to 110.28 mg/kg. The radish Pb concentrations were significantly different, lowest in Nau-Rg05, while the highest in Nau-Zdcb05. The Pb content of root negative correlated significantly with the root dry weight and the shoot dry weight.2. Pb Uptake Character and Stress Effect on the Growth and Antioxidant Enzymes Activities in Raphanus sativusThe effect of Pb on accumulation and antioxidative response were studied in Nau-Rg05 and Nau-Zdcb05 radish seedlings. The seedlings were treated with different concentrations of Pb (0-800mg/L) in the hydroponic system. It was indicated that radish genotype Nau-Zdcb05 accumulated more Pb than Nau-Rg05 and most of the Pb was accumulated in root and only a little was transported to shoot. The plant growth was inhibited under Pb stress, with the decrease of root length, fresh and dry weights. Excess Pb induced MDA contents increasing significantly and MDA in shoot was much higher than that in root, while the content of MDA in Nau-Rg05 was higher than that in Nau-Zdcb05. The antioxidant activities (SOD, POD, CAT and APX) increased in the roots at 100 mg/L Pb compared to control and followed by decreasing with the increasing Pb concentrations, indicating a direct correlation with Pb accumulation. Moreover, the antioxidant activities in root of Nau-Rg05 were higher than that in Nau-Zdcb05.3. Analysis of Genomic DNA Methylation Level in Radish under Lead Stress by Methylation-sensitive Amplified Polymorphism TechniqueThe MSAP ratios in radish seedling exposed to lead at the concentration of 100, 400 and 800 mg /L were 12.7%,14.2% and 17.0% respectively, higher than that in the control; the full methylation levels (C^mCGG in double strands) were at 9.7%,10.2% and 12.8% respectively, while the control was 9.5%. The level of increase in MSAP and full methylation indicated that de novo methylation occurred in some 5'-CCGG sites under Pb stress. There was significant positive correlation between increase of total DNA methylation level and Pb concentration. Four types of MSAP patterns: de novo methylation, de-methylation, atypical pattern and no changes of methylation pattern were identified among Pb treatments and the control. DNA methylation alteration in plants treated with Pb was mainly through de novo methylation.4. Genetic Analysis of Pb Accumulation in RadishRadish germplasms, Nau-Zdcb05 and Nau-Rg05, with large differences in Pb accumulation were choosen from general screenings and used to reveal the genetic mechanism of Pb accumulating ability in radish. Genetic analyisis were performed under major gene + polygene mixed inheritance model in the P₁, P₂, F₁ and F₂ of the cross Nau-Zdcb05 X Nau-Yh05. The results showed that Pb concentration in the cross was controlled by two major genes plus polygenes.