ALUMINUM INDUCES A DECREASE IN CYTOSOLIC CALCIUM-CONCENTRATION IN BY-2 TOBACCO CELL-CULTURES

Al toxicity is a major problem that limits crop productivity on acid s oils. It has been suggested that Al toxicity is linked to changes in c ellular Ca homeostasis and the blockage of plasma membrane Ca2+-permea ble channels. BY-2 suspension-cultured cells of tobacco (Nicotiana tab acum L.) exhibit rapid cell expansion that is sensitive to Al. Therefo re, the effect of Al on changes in cytoplasmic free Ca concentration ( [Ca2+](cyt)) was followed in BY-2 cells to assess whether Al perturbed cellular Ca homeostasis. Al exposure resulted in a prolonged reductio n in [Ca2+](cyt) and inhibition of growth that was similar to the effe ct of the Ca2+ channel blocker La3+ and the Ca2+ chelator ethyleneglyc ol-bis(beta-aminoethyl ether)-N,N'-tetraacetic acid. The Ca2+ channel blockers verapamil and nifedipine did not induce a decrease in [Ca2+]( cyt) in these cells and also failed to inhibit growth. Al and La3+, bu t not verapamil or nifedipine, reduced the rate of Mn2+ quenching of I ndo-1 fluorescence, which is consistent with the blockage of Ca2+- and Mn2+-permeable channels. These results suggest that Al may act to blo ck Ca2+ channels at the plasma membrane of plant cells and this action may play a crucial role in the phytotoxic activity of the Al ion.