A functional explanation for patterns of norditerpenoid alkaloid levels intall larkspur (Delphinium barbeyi)

Concentrations of norditerpenoid alkaloids vary among larkspur (Delphinium) species, locations, and years, but environmental stresses seem to have lit tle effect on alkaloid levels. There is a need for a functional hypothesis of alkaloid synthesis and metabolism to explain the observed trends in conc entration and to predict the toxicity of larkspur populations. This study w as replicated at two locations over two years in the mountains of central U tah. Ten tall larkspur (D. barbeyi) plants were marl;ed at each location, a nd a single stalk was harvested from each plant at weekly intervals through out the growing season. Concentrations of toxic and total alkaloids were me asured by Fourier-transformed infrared spectroscopy (FTIR), and alkaloid po ols were calculated by multiplying the alkaloid concentration by the dry we ight of the plant to determine the amount of alkaloids in the stalk. Alkalo id pools in the stalks increased for the first three weeks, leveled off, an d then declined to low levels as the plants began to senesce. Concentration s of alkaloids declined through the season, as the alkaloids were diluted i n the increasing biomass as the plants grew. These patterns will be used to predict potential toxicity of larkspur populations.