Seasonal variation in resource allocation of extractable compounds in Asclepias, Chrysothamnus and Grindelia

Abstract

The yields of whole plant hexane and methanol soluble extractables from Asclepias speciosa; Chrysothamnus itnauseosus subsp, consimilis and Grindelia squarrosa were examined throughout the growing season. The yields of non-polar extractables remained relatively constant during the growing season with increases in late summer or early fall according to the species. Each of the three taxa showed a similar pattern with the methanol soluble fraction reaching a maximum in June. However, a second maximum was observed in Asclepias and Grindelia in August. Protein content was examined in Asclepias and Grindelia and was found to decline throughout the growing season. Individual components of the hexane extract of Asclepias were examined and several components were found to vary seasonally. Principal components analysis of the nonpolar components revealed that the components with high intercorrelations were members of five chemical biosynthetic classes: alkanes, fatty acids, pentacyclic triterpenoids and tetracyclic sterols. Canonical variate analysis grouped the samples by date of sample from May to September-October.