Acidification of Deionized Water by Roots of Intact Rice Seedlings

This investigation was designed to examine whether or not deionized water could be acidified by roots of intact rice seedlings. Roots of intact rice seedlings caused significant acidification of the deionized water in which they were immersed and this acidification could be repeated after replacement of acidified water with fresh deionized water. The addition of K, Na, and Mg* to the deionized water significantly increased the rate and extent of acidification. However, no such increase was found when Ca was present in the water. The inhibition of acidification by vanadate and its promotion by fusicoccin indicated that the acidification of water by roots of intact rice seedlings originated from an ATP-driven proton pump located in the plasmalemma. Ferricyanide was effectively reduced by the roots of intact rice seedlings. This reduction was associated with the acidification of the bathing solution. 8-Hydroxyquinoline and p-nitrophenylacetate inhibited both the reduction of ferricyanide and ferricyanide-induced acidification. Vanadate, although it slightly inhibited the reduction of ferricyanide, did not inhibit the ferricyanide-stimulated decrease in pH. It seems that the involvement of redox activity associated with the plasmalemma in the acidification of deionized water cannot be excluded.