Rapid uptake of arsenite (AsⅢ) into barley roots

摘要

Arsenite is the dominant inorganic arsenic species under reducing conditions, such as those existing in the rhizosphere of paddy rice. Arsenite has high membrane permeability, in part due to it being uncharged at physiological pH. As a consequence, it seems unlikely that uptake into the cell is mediated by membrane transporters. In barley roots exposed to 20μM As(Ⅲ), uptake was biphasie, comprising a rapid initial influx followed by a slower linear component that continued for at least 6 days, at which time the internal concentration had risen to around 1200M. The accumulation of As(Ⅲ) was correlated with the synthesis of thiol compounds (R-SH), with a stoiehiometric ratio of 1.5-2 R-SH per As(Ⅲ). Increasing the As(Ⅲ) concentration above 10μM did not result in higher internal As(Ⅲ) or R-SH accumulation. It is proposed that the accumulation of As(Ⅲ) is limited by the rate of synthesis of thiol compounds and/or the rate at which arsenite-thiol complexes can be transported to the vacuole.