Abstract: Significant differences in the exudation and accumulation of citric acid in common bean genotypes were observed in response to Al toxicity stress by hydroponic cultural experiments. Secreted citric acid increased with increasing external concentrations of Al³⁺ which ranged from 0 to 50 μmol·L^-1,while ranged from 50 to 80 μmol·L^-1,secreted citric acid decreased with increasing external concentrations of Al³⁺. Among different genotypic common beans,citric acid secreted in G19842 was the largest,while Al uptake per unit dry weight in G19842 was the least. No difference in the accumulation of citric acid in leaves was found among different genotypic common beans,while the size of the content of citric acid in roots was G19842>AFR>ZPV>G5273. The amount of citric acid exuded was smaller induced by phosphorus deficiency than that induced by Al toxicity stress. Exposure to 50 μmol·L^-1 LaCl 3 could not induce the exudation of citric acid,and it implied that the exudation and accumulation of citric acid in common bean was an important physiological response of resistance to Al toxicity stress.

Key words: Al toxicity stress, Citric acid, Exudation and accumulation, enzyme activity, calcium, abscisic acid, photosynthesis, cucumber seedling