Inhibition of proton transport activity of microsomal membrane vesicles of barley roots by aluminium

Abstract

The extrusion of protons from the roots of barley (Hordeum vulgare L.) seedlings in the presence of KCl decreased markedly after treatment of the samples with 1 mm AlCl₃ at pH 5.5. The membrane vesicles with ATP-dependent proton transport activity were prepared from barley roots. The proton transport activity measured by the quenching of the fluorescence of quinacrine was inhibited by approximately 50% in the presence of 100 μm AlCl₃ at pH 6.5 but the inhibition was only 10% at pH 7.5. The values of V _max and K _m for ATP related to the proton transport activity of the vesicles were affected markedly by AlCl₃. The inhibition of the proton transport activity of the vesicles due to Al was effectively restored by citric acid. The results suggest that one of the mechanism of Al toxicity in plant roots is the inhibition of the proton transport activity associated with the cell membrane which in turn leads to the inhibition of proton extrusion from the roots.