Effect of aluminium on ion uptake and H+ release by maize

The aim of this study was to quantify the long-term effects of Al in solution on mineral ion uptake and associated H+ release by the roots of maize cultivated in conditionss compatible with field data. Two maize cvs of differing sensitivity to Al were compared. The culture was conducted in hydroponic conditions en the presence of 0-3 microM Al. Proton fluxes were localized along the roots using a videodensitometry method. Al reduced the uptake of anions, particularly NO3-, whereas the uptake of K+ and NH4+ was unaffected. These effects were accompanied by an increase in net H+ release which was quantitatively comparable with the reduction in NO3- uptake. The reduction in NO3- uptake and the concomitan increase in H+ release increased with the quantity of Al accumulated in the roots. The Al-sensitive cultivar bound more Al to its roots than the Al-tolerant one. These results led us to specify the relation between the Al deposition in roots, the reduction in NO3- uptake and the stimulation in rhizosphere acidification by the plant. They show Al induces an inhibition in NO3uptake and an increase in net H+ release in a 1:1 ratio. These concomitant effects suggests that inhibition in NO3-/OH- exchange unmasks active H+ excretion which is otherwise insensitive to Al. Both these effects are closely related to the Al content in roots expressed per unit root lengt