Mechanism of aluminum tolerance in snapbeans. Root exudation of citric acid

• Published in: Plant physiology (Bethesda) Vol. 96; no. 3; pp. 737 - 743
• Main Authors: Miyasaka, S.C. (University of Hawaii, Hawaii Branch Station, Hilo, HI), Buta, J.G, Howell, R.K, Foy, C.D
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01-07-1991
• Subjects: 560300 - Chemicals Metabolism & Toxicology; Acid soils; ACIDE CITRIQUE; ACIDO CITRICO; Adaptation to environment and cultivation conditions; Agronomy. Soil science and plant productions; ALUMINIO; ALUMINIUM; Aluminum; Biological and medical sciences; BIOLOGICAL AVAILABILITY; BIOLOGICAL STRESS; CARBOXYLIC ACIDS; CHELATING AGENTS; CITRIC ACID; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; CRECIMIENTO; CROISSANCE; ELEMENTS; EXSUDAT; EXUDADOS; FITOTOXICIDAD; Fundamental and applied biological sciences. Psychology; Genetics and breeding of economic plants; HYDROXY ACIDS; LEGUMINOSAE; MAGNOLIOPHYTA; MAGNOLIOPSIDA; METALS; NONMETALS; Nutrient solutions; ORGANIC ACIDS; ORGANIC COMPOUNDS; PHASEOLUS; PHASEOLUS VULGARIS; Phosphates; PHOSPHORUS; PHYTOTOXICITE; Plant roots; PLANTS; RACINE; RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT; RAICES; Rhizosphere; Seedlings; SENSITIVITY; SOILS; TOLERANCE; TOXICITY; VARIACION GENETICA; VARIATION GENETIQUE; VARIEDADES; Varietal selection. Specialized plant breeding, plant breeding aims; VARIETE; Root; Tolerance; Aluminium; Organic acids; Citric acid; Stress; Rhizosphere; Phytotoxicity; Leguminosae; Vegetable crop; Phaseolus vulgaris; Dicotyledones; Hydroponic cultivation; Angiospermae; Chelation; pH; Spermatophyta; Exudation; Cultivar
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.96.3.737

One proposed mechanism of aluminum (Al) tolerance in plants is the release of an Al-chelating compound into the rhizosphere. In this experiment, two cultivars of snapbeans (Phaseolus vulgaris L. "Romano" and "Dade") that differ in Al tolerance were grown hydroponically with and without Al under aseptic conditions. After growth in nutrient solutions for 8 days, aliphatic and phenolic organic acids were analyzed in the culture solutions with an ion chromatograph and a high pressure liquid chromatograph. The tolerant snapbean, "Dade", when exposed to Al, exuded citric acid into the rhizosphere in a concentration that was 70 times as great as that of "Dade" grown without Al, and 10 times as great as that of "Romano" grown with or without Al. The sensitive cultivar, "Romano", exuded only slightly more citric acid into the growing medium under Al-stress, compared to nonstressed conditions. Citric acid is known to chelate Al strongly and to reverse its phytotoxic effects. Also, citric acid has been shown previously to enhance the availability of phosphorus (P) from insoluble Al phosphates. Thus, one mechanism of Al-tolerance in snapbeans appears to be the exudation of citric acid into the rhizosphere, induced either by toxic levels of Al or by low P due to the precipitation of insoluble Al phosphates. Our experiment was not able to distinguish between these two factors; however, tolerance to both primary and secondary Al-stress injuries are important for plants growing in Al-toxic soils