Effects of Zn on Subcellular Distribution and Chemical Forms of Cd in Potentilla griffithii var.velutina

Using the differential centrifugation technique and sequential chemical extraction methods,effects of Zn on subcellular distribution and chemical forms of Cd under nutrient solution culture were studied to understand the influence of Zn on Cd tolerance in Zn hyperaccumulator Potentilla griffithii var.velutina.The results showed that 72%～95% of total Cd were bound to cell wall and soluble fraction in the plant,and only a small quantity of Cd distributed in chloroplast,karyon and mitochondrion,which suggested that cell wall and soluble fraction in the plant were major storage sites for Cd.Moreover,cell wall binding Cd fraction increased with the increasing of Cd or Zn concentrations in the nutrient solution.As to Cd chemical forms,73%～93% of total Cd existed as water-and ethanol-extractable forms in the plants under the control,and 86%～96% of total Cd existed as NaCl-,water-and ethanol-extractable Cd forms in other treatments.Whereas NaCl-extractable form,accounting for 42%～78% of total Cd,was dominant in Zn/Cd compound treatments.The percentage of NaCl-extractable Cd form increased but those of ethanol-and water-extractable Cd forms decreased with the increasing of Cd or Zn concentration,which indicated that Cd or Zn addition facilitated the transferring of Cd from relatively higher active chemical forms to less active ones.The results mentioned above indicate that cell wall binding,vacuolar compartmentalization in the soluble fraction and transferring to lower active chemical forms are main tolerance mechanisms for Cd in Potentilla griffithii var.velutina.