Short Communication Aluminum Stress Increases K+ Efflux and Activities of ATP- and PPj-Dependent H + Pumps of Tonoplast-Enriched Membrane Vesicles from Barley Roots

Aluminum stress significantly stimulated K+ efflux from barley roots that had been preload-ed with K+. The stress also increased P P r and ATP-dependent H+ pump activities of tonoplast-enriched membrane vesicles from the roots. Ca2+ ions reduced increases in K+ effux and both H + pump activities under these conditions. Key words: Al stress — Hordeum vulgare. — H + pumps — K+ efflux — Tonoplast. Aluminum (Al) is one of the major elements in soil. Solubilized Al ions in acid soil, often at pH values below 5.5, have long been known to have a toxic effect on the growth of plants. Therefore, the harmful effects of acid soil on plant growth are closely related to Al toxicity. Various efforts have been made to solve the problem of Al toxicity using crop plants (Foy 1988). Clarification of the mechanism of Al toxicity or tolerance to Al is impor-tant but it is still difficult to define any unifying features of the results from the many published physiological and bio-chemical studies. It seems likely from research published to date that the physiological injuries caused by Al stress are largely de-pendent on the effects of Al on the functions of the various plant cell membranes. The preferred association of phos-phorus in membrane phospholipids with positively charge