We characterised the physiological mechanisms of tolerance in two beanvarieties (Phaseolus vulgaris L. viz. French Bean cv. Amy and Rosecoco(GLP2» differing in Al tolerance of the varietal level. Root elongation atvarying levels of Al over time clearly showed the Al tolerance superiority of Rosecoco over French bean. Aluminium uptake was much higher in French bean, in both root apex and 2 mm region of the root apex. The root cationexchange capacity of the AI-sensitive French bean was markedly higher thanthat of Rosecoco. Citric acid was the only organic acid whose secretion was stimulated by Al and was higher in Rosecoco than in French bean. The citrate synthase and NADP+-isocitrate dehydrogenase activities were apparently higher in Rosecoco than in French bean b1,lt those of phosphoenolpyruvate carboxylase were not significantly different between the two varieties under Alstress. Triphenyl-tetrazolium chloride (TTC) reduction was greater in Rosecoco and was also well correlated with the citrate secretion. These results suggest the role of TTC reduction and citrate secretion as underlying factors in the Al tolerance mechanism of Rosecoco

DOI: 10.1080/00380768.2000.10409159