REDUCTION OF Cr(VI) TO Cr(III): A DETOXIFICATION MECHANISM IN HYPERACCUMULATOR LEERSIA HEXANDRA SWARTZ

The mechanisms underlying the detoxification of Cr(VI) by Leersia hexandra Swartz, a Cr-hyperaccumulator, remain unclear. To determine whether L. hexandra was able to detoxify Cr(VI) by reduction, we studied the oxidation state and possible complexation mode of Cr in plant tissues using non-destructive techniques, namely, XANES and EPR spectroscopy. In L. hexandra, treated with Cr(VI) solution, XANES and EPR indicated that highly toxic Cr(VI) was reduced to the intermediate Cr(V) and accumulated as less toxic Cr(III), and reduction of Cr(VI) mainly depended on the chemical reduction of Fe(III) and the complexation of organic acid. We also aimed to analyze the possible complexation mode of Cr in Cr(III)- and Cr(VI)-treated L. hexandra. In roots, Cr was accumulated in the form of Cr(OH)(3). A portion of Cr in roots was possibly bound to organic acid ligands, which promoted the translocation of Cr. However, The Cr in leaves was was primarily Cr(III)-trioxalate, with small amounts of Cr(III)-dioxalate and Cr(III)-citrate, and a small amount of Cr(OH)(3) were also found. Therefore, oxalate was the final receptor of Cr in the vacuole.