Acute drought stress and plant age effects on alkamide and phenolic acid content in purple coneflower roots.

The effects of acute periods of drought stress on dry weight, and alkamide and phenolic acid content in purple coneflower [Echinacea purpurea (L.) Moench, Asteraceae] roots are described. Plants subjected to brief drought stress periods for two seasons during the initial flowering stage (D-F2) produced fall-harvested roots with significantly greater cichoric acid concentration (mg/g) than corresponding well-watered controls of the same age (C-2). Total alkamide, including the tetraenoic acid isomers, and chlorogenic acid concentrations from fall-harvested roots were largely unaffected by drought stress, regardless of when the stress occurred developmentally. The alkamide concentration in three-year roots was significantly less than that in two-year roots, with an average decrease of 50.5 %. Conversely, total phenolic acids increased an average of 67.1 % for all treatments from two to three years of age. Root dry weight increased significantly by an average of 70.0 % for all drought-stressed plants from two to three years of age, compared to an increase of 35.2 % for well-watered controls. The results suggest that controlled drought stress can stimulate increased root dry weight and root cichoric acid content, and that root age is the predominant factor determining overall phytochemical content variation.