Seasonal flux of isothiocyanate-yielding glucosinolates in roots, stems and leaves of Cardamine cordifolia

Concentrations of constituent isothiocyanate-yielding glucosinolates (IYG) declined seasonally in cauline leaves and stems of Cardamine cordifolia, sampled in montane Colorado. All five constituents (isopropyl, 2-butyl, isobutyl, benzyl and 2-phenyl-ethyl glucosinolates) were correlated positively with total concentration over the growing season. In contrast, no seasonal decline was discerned for total and constitutent IYG concentrations in roots and basal leaves, and constituents showed a mixed pattern of positive and negative correlations with total amount. Vegetative organs thus constitute two compartments relative to glucosinolate metabolism. In above-ground stems and associated cauline leaves, IYG concentrations decline individually and in concert over the growing season. In below-ground rhizomes and associated roots and basal leaves, individual compounds fluctuate in concentration, but in the aggregate do not decline seasonally. Metabolic fluxes of individual glucosinolates within and between vegetative organs, as well as changes in total concentrations, may influence feeding by herbivores.