Aluminum-Enhanced Proton Release Associated with Plasma Membrane H+-Adenosine Triphosphatase Activity and Excess Cation Uptake in Tea (Camellia sinensis) Plant Roots

Abstract

Cultivated tea (Camellia sinensis) plants acidify the rhizosphere, but the mechanisms responsible for rhizosphere acidification associated with aluminium (Al) have not been fully elucidated. The present study examined the effect of Al on root-induced rhizosphere acidification, plasma membrane H+-ATPase activity and the cation–anion balance of tea plants. The H+ exudation from tea plant roots with or without Al treatment was visualized using an agar sheet with bromocresol purple. Al strongly enhanced H+ exudation and the acidification of tea plant roots by Al was closely associated with plasma membrane H+-ATPase activity. Detection of H+-ATPase hydrolytic activity associated with plasma membranes of roots under different Al treatments using the two-phase partition system indicated that plasma membrane H+-ATPase activity increased with Al concentration. The Al content, amount of proton release and H+-ATPase activity in the roots of tea plants were quantified after 7 days with or without Al. The Al content, amount of proton release and H+-ATPase activity were significantly higher in roots with Al treatment than those without Al treatment. The value for the cation–anion balance showed that all treatments had an excess of cations relative anions, and the amount of excess cations uptake increased with the increasing Al concentration. The results suggested that Al-enhanced proton release was associated with plasma membrane H+-ATPase activity and excess cation uptake. Taken together, these findings provide insights into the contributing factors of soil acidification in tea plantation.