Vacuolar Compartmentalisation And Efflux Of Cadmium In Barley

Plants have developed different tolerance strategies to deal with toxic metals. Various factors and mechanisms related to the compartmentalisation of cadmium (Cd) into the vacuoles and the efflux of Cd were investigated to analyse their roles in Cd tolerance in barley. In vacuolar transport assays, the addition of adenosine triphosphate (ATP) alone significantly increased Cd uptake into the vacuole, but more so when both ATP and glutathione (GSH) were supplied together. This suggests that Cd may be partly sequestered as Cd2+ ions via divalent cation transporters, but predominantly as Cd-GSH complexes, most likely via ATP-binding cassette transportertype transporters. Comparison of the concentrations of Cd-109 in whole protoplasts and vacuoles isolated from shoots demonstrated that the majority of the cellular Cd was located in the vacuole. Over 48 h, 12% of the root Cd was effluxed into the external solution when roots were loaded with Cd-109 by foliar application. This active excretion may be a detoxification strategy, in addition to the compartmentalisation of the majority of cellular cadmium into vacuoles predominantly as complexed form.