CORRELATION BETWEEN ENDOGENOUS TANNINS AND LEAD ACCUMULATION IN ROOTS OF SYMPHYTUM OFFICINALE L.

摘要

Metal-chelating tannins may help plants tolerate heavy metals. However, there is a lack of evidence linking endogenous tannin levels with lead accumulation in plants tested for phytoremediation. This study strengthens this possible link by finding a correlation between lead accumulation and the different concentrations of tannins in main and lateral roots of Symphytum officinale (comfrey) plants, following treatment with lead-based solutions (with and without EDTA). The concentration of tannins in lateral roots (8.9 mg tannic acid g~(-1) dry weight) was more than three times greater than in main roots and was unaffected by either lead treatment. Lead accumulation was found to be ten times greater in the lateral roots (2375 mg kg~(-1)) than in main roots and, using transmission electron microscopy, more lead was observed in lateral roots. These results suggest that roots with more endogenous tannins may accumulate more lead, and therefore tannin levels may be used as a characteristic for selecting plants for phytoremediation.