Responses of Astragalus tennesseensis to drought : Changes in free amino acids and amides during water stress and possible ecological significance.

In order to better understand the adaptations of Astragalus tennesseensis Gray (Leguminosae) to its summer-dry cedar glade habitat, comparisons were made of the free amino acids and amides in leaves of drought- and nondrought-treated plants. No qualitative differences were detected; 13 free amino acids and 2 amides were identified. However, water stressed plants showed a 115% increase in the total amount of amino acids and amides over nondrought stressed plants. Proline accounted for 30.1% of the increase and aspartic acid 37.1%. Water stress caused an increase in the 2 amides and in 11 of the 13 amino acids; alamine and serine decreased. Upon rewatering, the total amount of amino acids and amides quickly decreased. The ability to accumulate proline and aspartic acid may be of adaptive value to A. tennesseensis during short periods of drought.