Effects of exogenous zinc on the accumulation of zinc and chromium and polyphenols in flue-cured tobacco under chromium stress

【Objective】This study was to explore the effects of different zinc(Zn) concentrations on the accumulation of chromium(Cr), Zn and polyphenols in flue-cured tobacco under Cr stress, so as to provide theoretical basis for the prevention and remediation of heavy metal pollution in flue-cured tobacco planting.【Method】Employing the pot experiment to simulate the single Zn(20, 60 and 100 mg/kg) pollution and the contamination treatment of Znand Cr(Cr was 15, 30 and 90 mg/kg), the treatment without adding Zn and Cr was selected as the control.On the 50^th day and 80^th day after transplanting, tobacco leaves of the 7 to 11 leaf positions were taken to determine the contents of chlorogenic acid, scopoletin and rutin;on the 80^th day after transplanting, the biomass, Cr and Zn absorption of tobacco plants were determined from three parts of tobacco(root, stem, leaf), the data were analyzed by significance test, two-way ANOVA and Pearson correlation analysis.【Result】Under single Zn stress, the biomass of tobacco plants increased firstly and then decreased with the increase of Zn concentration.The biomass of 60 mg/kg Zn treatment was the highest, and the roots, stems and leaves biomass increased by 28.1%, 14.5% and 7.4% respectively compared with the control.Under the Zn and Cr combined pollution, the biomass of tobacco plants treated with 15 mg/kg Cr was not greatly different from that of the control, while the biomass of 90 mg/kg Cr treatments was lower than that of the control.Single Zn had obvious effect of low concentration promoting and high chromium inhibiting the absorption of Cr in the roots of tobacco plants, and reduced Cr contents and promoted Zn accumulation in leaves.Under the combined treatment of Zn and Cr, the accumulations of Cr in tobacco roots was increased and that of Zn was decreased.At the same time, the Cr contents of compound treatments in tobacco leaves were decreased by 41.9%-72.7% compared to control, while the Zn content of tobacco leaves was lower than that of the control except for 15 mg/kg Cr combined with Zn.Exogenous addition of Zn could reduce the tobacco leaf Cr bioaccumulation factor(BAF).Except for the combined treatment of 0 and 15 mg/kg Cr and 100 mg/kg Zn, the stemand leaf/root translocation factor(TF) of the other treatments were lower than the control.Single Zn could promote the accumulation of chlorogenic acid, rutin and scopoletin in tobacco leaves.The soil Zn/Cr addition ratios at 20/15, 60/15, and 100/15 were beneficial to the accumulation of chlorogenic acid and rutin in tobacco leaves under Cr and Zn combined stress.【Conclusion】Adding exogenous Zn can reduce the Cr accumulation in tobacco leaves.The high soil Zn/Cr addition ratios can promote the accumulation of Zn, chlorogenic acid and rutin in the tobacco leaves, and inhibit the accumulation of Cr in the roots.It can be considered to adjust the ratio of Cr and Zn in the soil by adding Zn element to reduce the content of Cr in tobacco leaves and regulate the accumulation of polyphenols in tobacco leaves.