Effects Of Foliar Application Of Zinc Fertilizer On The Bioaccessibility Of Cadmium And Zinc In Brassica Chinenesis L.

The pollution of cadmium（Cd）in farmland soils in our country is becoming more and more serious.Vegetables have a strong ability to uptake and accumulate Cd from soils,and thus become one of the main sources of dietary Cd intake in humans.Cd enters the human body through the food chain,which seriously threatens human health.Therefore,it is necessary to reduce the Cd concentrations in vegetables,especially leafy vegetables,to ensure the safe production of vegetables.Zinc（Zn）is a trace element necessary for the growth and development to plants and human.In this study,to explore the effect and regulation mechanism of foliar Zn on health risks of Cd and Zn in Brassica chinenesis L.,a pot experiment was used to plant two cultivars of Brassica chinenesis L.with different Cd accumulation ability.The in vitro digestion method was used to study the effect of spraying different forms and concentrations Zn fertilizer on the Cd and Zn concentrations and bioaccessibility in Brassica chinenesis L.On this basis,by analyzing the subcellular fractions and chemical form of Cd and Zn,as well as the phytic acid,sulfhydryl compounds and sulfur-containing amino acid,combined with correlation analysis and linear correlations methods to explore the mechanism of spraying Zn fertilizer on the bioaccessibility of Cd and Zn.This study can provide new ideas and technical support for the prevention and safe utilization of Cd-contaminated vegetable in China.The main results of this study are as follows:（1）A pot experiment,spraying different concentrations of ZnSO₄ and EDTA-Zn on two cultivars of Brassica chinenesis L.（the common cultivar Hanlv and the low-Cd accumulating cultivar Huajun）in acid（Xiangtan）and neutral（Jiyuan）Cd-contaminated soil,was conducted to study the effects of foliar Zn fertilizer on biomass,Cd concentrations,Cd bioaccessibility,subcellular fractions and chemical form of Zn in Brassica chinenesis L.The results showed that foliar ZnSO₄ had no significant effect on the biomass and Cd concentrations in the shoots,but inhibits the digestion and dissolution of Cd in the gastric and small intestine phases.Foliar EDTA-Zn inhibited the growth,increases the Cd concentrations in the shoots,and promotes the digestion and dissolution of Cd in the small intestine phases.Foliar ZnSO₄ decreased the Cd ratio in organelles,while foliar EDTA-Zn decreased the Cd ratio in cell wall and increased in cell soluble components.The mainly chemical forms of Cd in the shoot were Na Cl and water extractable.Foliar ZnSO₄ decreased the water and increased the Na Cl extractable Cd ratio in Jiyuan soil.Foliar EDTA-Zn increased ethanol and water and decreased Na Cl extractable Cd ratio.Correlation and linear fitting analysis showed that cell soluble fractions,ethanol and water extracted Cd contribute the most to the digestion and dissolution of Cd.Foliar Zn regulated the bioaccessibility of Cd by affecting these subcellular and chemical form fractions.（2）A pot experiment,spraying different concentrations of ZnSO₄ and EDTA-Zn on two cultivars of Brassica chinenesis L.in acid and neutral Cd-contaminated soil,was conducted to study the effects of foliar Zn fertilizer on Zn concentrations,bioaccessibility,subcellular fractions and chemical form of Zn in Brassica chinenesis L.The results showed that foliar Zn fertilizer significantly increased the Zn concentrations of the shoots and bioaccessible Zn concentrations in the gastric and small intestine phases.Foliar ZnSO₄ increased Zn ratio in the cell wall and decreased in the organelle.Foliar EDTA-Zn increased Zn ratio in the soluble fraction and decreased Zn ratio in the cell wall and organelle.Foliar Zn fertilizer increased the Zn concentrations of each chemical form fractions,with the increasing of foliar Zn concentration.Foliar ZnSO₄ increased the Zn ratio of Na Cl and acetic extractable fractions and decreased ethanol and hydrochloric extractable fractions.Foliar EDTA-Zn increased the Zn ratio of ethanol and water extractable fractions and decreased other forms.Correlation and linear fitting analysis showed that cell soluble fractions,ethanol and water extracted Zn are most easily digested and dissolved during the gastric and small intestine phase.Foliar Zn regulated the bioaccessibility of Zn by affecting these subcellular and chemical form fractions.（3）A pot experiment,spraying 4 mmol·L^-1 ZnSO₄ and EDTA-Zn on two cultivars of Brassica chinenesis L.in acid Cd-contaminated soil,was conducted to study the effects of foliar Zn fertilizer on Cd and Zn concentrations and bioaccessibility,phytic acid,sulfhydryl compounds and sulfur-containing amino acid concentrations in Brassica chinenesis L.The results showed that foliar Zn fertilizer application had no significant effect on the Cd concentrations and Cd bioaccessibility in the gastric phase,while significantly increased the Zn concentrations in the shoots and decreased Zn bioaccessibility in the gastric and small intestine phase.Foliar EDTA-Zn significantly increased Cd bioaccessibility in the small intestine phase.Foliar ZnSO₄ significantly increased phytic acid concentrations in Hanlv,while foliar EDTA-Zn decreased it.Foliar Zn fertilizer had no significant effect on the total sulfhydryl concentrations,significantly reduced protein sulfhydryl concentrations in Huajun,and significantly increased non-protein sulfhydryl and phytochelatins concentrations.Foliar ZnSO₄significantly increased the glutathione concentrations in Huajun and methionine in Hanlv.Foliar EDTA-Zn significantly reduced the glutathione and cysteine concentrations in Hanlv.Correlation and linear fitting analysis showed that the phytic acid,glutathione and methionine in the shoots of Brassica chinenesis L.were not conducive to the digestion and dissolution of Cd and Zn,while Cysteine contributes to it.Foliar Zn fertilizer affected the Cd and Zn bioaccessibility by comprehensively regulating these physiological indicators.