| With the improvement of people's living quality and requirement to the dietary nutrition,vegetable consumption is increasing year by year.However,due to the serious soil heavy metal contamination and the reports of food safety incidents in recent years,concerns on vegetable safety production have been greatly raised.Therefore,this study is dedicated to screen high-and low-Cd accumulation leaf mustard from production practice and further explores their Cd uptake and transport mechanisms,in order to clarify the physiological differences between high-and low-Cd accumulation mustard varieties,and provide theoretical basis for vegetable safety production and research direction for low-Cd mustard cultivation.The research revealed that the difference of Cd content in shoots between high-and low-Cd accumulation leaf mustard varieties screened mainly due to the difference of Cd uptake and accumulation in its root.The main results are:1?Screening for high-and low-Cd accumulation cultivarsA high-and a low-Cd accumulation leaf mustard cultivars were screened by statistical analysis combining with production practice,which are low-Cdcultivar accumulation(Bianha more pulp leaf mustard)and high-Cd accumulation(cultivarShuidong sweet and crisp leaf mustard),respectively.2?The Cd translocationof the high-and low-Cd accumulation cultivarsCorrelation analysis found that Cd concentrations between xylem sap and culture media had significant positive correlation(p<0.05),in both high-and low-Cd accumulation mustard cultivars.However,the Cd accumulation in shoots was not linearly correlated with that in xylem,which indicated that antagonistic effect was existed during the xylem loading and transport processes.Variance analysis found that the two mustard cultivars had significantly different Cd accumulation rate in xylem(p<0.05),whereas they had quite similar Cd translocation coefficients(p>0.05).This might be due to the different xylem loading rates between these two varieties.These results also indicated from the side that root-shoot transport process is not a major determinant for Cd accumulation in shoots of leaf mustard.3?Subcellular distribution of Cd in roots of the high-and low-Cd accumulation cultivarsWe found that low-and high-Cd accumulation mustard cultivars also differed greatly in Cd subcellular distribution in roots(p<0.05).In low-Cd accumulation cultivar,the proportion of Cd adsorbed in cell walls increased as Cd concentration in culture media increased,while root soluble Cd decreased.Thus,it could be speculated that cell wall sequestration is an important means for Cd detoxification in low-Cd accumulation cultivar.The Cd fractions in roots were also extracted by ethanol,NaCl,acetic acid and HCl.Results showed that ethanol-,NaCl-,acetic acid-and HClextracted Cd concentrations in low-Cd accumulation cultivar had significant difference in comparison to those of high-Cd accumulation cultivar(p<0.05),in particular for acetic acid-and HCl-extracted Cd,the proportions of which were increased in Cd treatments.Therefore,low-Cd accumulation cultivar may reduce Cd root-shoot transport by transforming mobile Cd to inactive forms in roots.4?Characteristic of root exudates of the high-and low-Cd accumulation cultivarsBy studying the Cdaccumulation and root exudates in different Cd accumulation mustard cultivars,we found that high-Cd accumulation cultivar enriched significant higher Cd in root than low-Cd accumulation cultivar(p<0.05).In the root exudates of high-Cd accumulation cultivar,3-methyl-2-oxobutanoic acid was significantly higher than other organic compounds.While in the the root exudates of low-Cd accumulation cultivar,3-methyl-2-oxobutanoic acid was only detected in high Cd treatment.Therefore,it could be speculated that 3-methyl-2-oxobutanoic acid can promote root uptake of Cd from outside media. |
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