Aluminum tolerances of two snapbean cultivars related to organic acid content evaluated by high‐performance liquid chromatography

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Abstract
High‐performance liquid chromatography (HPLC) was used to determine aluminum (Al)‐induced changes in organic acid (OA) concentrations of Al‐tolerant ‘Dade’ and Al‐sensitive ‘Romano’ snapbean cultivars. Two week old ‘Dade’ and ‘Romano’ snapbean were grown in 1/5‐strength Steinberg nutrient solution for 10 days and then subjected to 0, 2, 4, 6, and 8 mg L‐1 Al treatments at pH 4.5 for an additional 3–15 days. Current studies confirmed earlier findings that the Dade cultivar was significantly more tolerant to Al than the Romano variety. Organic acid analyses were performed on extracts of root and leaf, and on stem exudates. The organic acids were separated on an ion exclusion column using a mobile phase of 0.01 N H3PO4. Individual OA were quantified with a variable wavelength detector operating at 210 nm. Aluminum stress tended to reduce the concentrations of citric, malonlc, malic, glycolic, fumaric, and acetic acids in the roots and increased the OA concentrations in stem exudates. In the presence or absence of Al stress, the Al tolerant Dade cultivar contained higher OA concentrations than did the Al‐sensitlve Romano. Aluminum stress reduced total OA levels in root extracts from Al‐sensltive Romano plants to a greater extent than in those of the Al‐tolerant Dade. Malic and citric acid concentrations were decreased more than those of the other organic acids examined. Results indicate that the Al‐tolerant Dade snapbean cultivar has a higher potential for Al‐chelation and detoxification than does the Al‐sensitive Romano. Hence, an Al‐chelation mechansism may be involved in differential Al tolerance within this species.