Differential aluminum tolerances of two barley cultivars related to organic acids in their roots

Abstract

‘Dayton’ barley is significantly more tolerant to excess Al in acid soils and nutrient solutions than is ‘Kearney’ barley; however, the physiological or biochemical mechanisms of such differential tolerance have not been clearly established. One hypothesis is that Al‐tolerant plants contain and exude organic acids or other ligands that form stable chelates with Al and thereby reduce its chemical activity and toxicity. The objective of our study was to determine the effects of Al on concentrations of organic acids in the roots of Al‐tolerant Dayton and Al‐sensitive Kearney barley cultivars. Plants were grown for 17 days in nutrient solutions containing 0, 55 and 110 μM Al (initial pH 4.5), and their roots were analyzed for organic acids by high performance liquid chromatography.

Aluminum stress significantly reduced concentrations of citric, succinic and total organic acids in the roots of Al‐sensitive Kearney barley but not in those of Al‐tolerant Dayton. Aluminum decreased concentrations of levulinic acid much more than citric acid, and to a much greater degree in Kearney than in Dayton. Hence, in the presence of Al, organic acids in the roots of the Al‐tolerant Dayton cultivar were protected from destruction, or the production of these acids was maintained more effectively than in the Al‐sensitive Kearney.

Further study is needed on the distribution and chemical states of Al in plants to assess the possible role of Al‐organic acid chelation in differential Al tolerance.

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Key words:

• Hordeum vulgare (L.)
• acid soils
• Al toxicity
• high performance 1iquid chromatography (HPLC)
• plant breeding
• low‐input agriculture