Effects of zinc on distribution and chemical form of lead in Potentilla griffithii var. velutina

The effect of Zn on tissue,subcellular distribution and chemical form of Pb in Potentilla griffithii var.velutina under hydroponic culture were studied using gradient centrifugation and sequential chemical extraction.Besides the control,other treatments showed 79%～88%,47%～77% and 13%～45% of total Pb in the plant were distributed in root,cell wall and soluble fraction,respectively.Although the addition of Zn had no influence on the overall pattern of subcellular distribution of Pb:cell wall soluble fraction karyon and chloroplast mitochondria,the addition of Pb and Zn generally increased the percentage of Pb in the cell wall and reduced it in the soluble fraction,suggesting that cell wall binding has been strengthened.As to the chemical forms,82%～89% of total Pb existed in an ethanol-and water-extractable form in the control,whereas 28%～60% of total Pb was in an HCl-extractable form in other treatments.The addition of Pb and Zn generally reduced the percentage of ethanol-and water-extractable Pb,meaning the chemical form of Pb was transferred from relatively active forms to less active forms.In conclusion retention in root,binding to cell wall,vacuolar compartmentalization in the soluble fraction and conversion of Pb to a less active chemical form were the main tolerance mechanisms for Pb in P.griffithii var.velutina.