EFFECTS OF BIOLOGICAL INHIBITORS ON KINETICS OF ALUMINUM UPTAKE BY EXCISED ROOTS AND PURIFIED CELL-WALL MATERIAL OF ALUMINUM-TOLERANT AND ALUMINUM-SENSITIVE CULTIVARS OF TRITICUM-AESTIVUM L

The effects of biological inhibitors on the kinetics of aluminium (Al) uptake by excised roots and purified cell-wall material of two Al-tolerant and two Al-sensitive cultivars of Triticum aestivum were investigated. In excised roots, treatment with 2,4-dinitrophenol (DNP) increased rates of Al uptake by 52 % and 73 % in Al-tolerant cultivars, but only by 7 % and 25 % in Al-sensitive cultivars. Gramicidin increased rates of Al uptake by 22 % and 61 % in Al-sensitive cultivars, while those of Al-tolerant cultivars were not affected. The combined effects of gramicidin and DNP on Al uptake were synergistic in Al-tolerant cultivars and multiplicative in Al-sensitive cultivars. Further investigations included fractionation of excised roots after absorption and desorption in vivo. In these experiments, kinetics of Al uptake in purified cell-wall material was unaffected by gramicidin, while increased uptake in the cell wall fraction was observed with DNP and DNP plus gramicidin. In contrast, in vitro uptake of Al by purified cell-wall material was unaffected by both DNP and gramicidin, suggesting that accumulation of Al in the cell-wall depends on the existence of a functional plasma membrane and/or cellular integrity. In all experiments with purified cell-wall material, no differences were observed between Al-tolerant and Al-sensitive cultivars. Thus, differences in the kinetics of Al uptake by excised roots could not be accounted for simply by differences in Al uptake into the cell wall. While the physiological basis of Al tolerance is still not clear, the effects of biological inhibitors on the kinetics of Al uptake by excised roots and purified cell-wall material in Al-tolerant and Al-sensitive cultivars provide experimental evidence that is consistent with the operation of an energy-dependent exclusion mechanism.