[Effects of cadmium and lead on subcellular distribution and chemical form of zinc in Potentilla griffithii var. velutina].

Using the differential centrifugation technique and sequential chemical extraction method, effects of Cd, Pb and different Zn salts on subcellular distribution and chemical form of Zn in Zn hyperaccumulator Potentilla griffithii var. velutina under nutrient solution culture were analyzed. Under all treatments except for the control, 46%-74% and 16%-33% of total Zn in the plants are distributed in cell wall and in soluble fraction, respectively. Further, 74%-95% of total Zn are localized in these two parts under all treatments, which suggest that cell wall and soluble fraction in the plant are major storage sites for Zn. Compared with the control, Zn percentage significantly increases by 9%-38% in the cell wall and decreases by 6%-40% in the soluble fraction with addition of Zn, Cd and Pb treatment (p < 0.05). Although the addition of Cd and Pb has no influence on the pattern of Zn subcellular distribution presenting cell wall > soluble fraction > karyon and chloroplast > mitochondrion, it generally reduces Zn percentage in the chloroplast, karyon and mitochondrion and increases that in the cell wall or soluble fraction, suggesting that Cd and Pb promote the transferring processes of Zn from organelle to either cell wall or vacuole. As to the chemical forms, 61%-87% of total Zn exist as ethanol- and water-extractable forms in plants under control and only leaves under Zn addition treatment; while 62%-73% of total Zn exist as NaCl- and ethanol-extractable forms in leafstalks and roots under Zn addition treatment. NaCl-, ethanol- and water-extractable forms are also the main chemical forms in the plants, occupied almost 70%-89% of total Zn under Zn/Cd and Zn/Pb compound treatments. The addition of Zn, Cd and Pb generally increases the percentage of NaCl-extractable Zn forms, but decreases that of ethanol-extractable Zn, which facilitates Zn chemical form transferring from relatively higher active forms to less active ones. These results mentioned above indicate that cell wall binding, vacuolar compartmentalization and reduction of total percentage in higher active chemical forms are main tolerance mechanisms for Zn in Potentilla griffithii var. velutina in response to Zn, Zn/Cd and Zn/Pb treatments. Additionally, different Zinc salts have no obvious influence on Zn subcellular distribution in the plant, whereas the treatment of Zinc nitrate turns Zn ethanol-extraction to a dominant chemical form.