Submitted to: Journal of Chemical Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/2/2000
Publication Date: 7/1/2000
Citation: Ralphs, M.H., Gardner, D.R., Pfister, J.A. 2000. A functional explanation for patterns of norditerpenoid alkaloid levels in tall larkspur (delphinium barbeyi). Journal of Chemical Ecology. Interpretive Summary: Concentration of larkspur alkaloids vary between species, locations and years; but environmental stresses seem to have little effect on alkaloid levels. There is a need for a functional hypothesis that describes larkspur alkaloid synthesis which can be used to predict toxicity of larkspur populations. Alkaloid concentration is not a good measure of alkaloid levels in the plant because concentration is relative to the othe components within the plant, as well as the plants biomass. Therefore, alkaloid pools were defined to represent the total amount of alkaloids in larkspur stalks. Alkaloid pools increased in larkspur stalks during the first 3-4 weeks of growth, leveled off during weeks 4-6, then declined to very low levels as the plants began to sensece. We hypothesize that alkaloid synthesis occurs during the first 3 weeks of growth, thus accounting for the increase in pool size. As the plant continues to grow, the alkaloids are diluted in the increasing biomass. As larkspur begins t flower, there appears to be a catabolism or translocation of the alkaloids out of the stalk, thus accounting for the rapid decline in the pools at the end of the season. These alkaloid patterns will be used to predict potential toxicity of larkspur populations.
Technical Abstract: Concentration of norditerpenoid alkaloids vary between larkspur (Delphinium spp.) species, locations, and years; but environmental stresses seem to have little effect on alkaloid levels. There is a need for a functional hypothesis of alkaloid synthesis and metabolism to explain the observed trends in alkaloid concentration, and to predict the toxicity of larkspur populations. This study was replicated at two locations and two years in the mountains of central Utah. Ten tall larkspur (D. Barbeyi) plants were marked at each location and a single stalk was harvested from each plant at weekly intervals throughout the growing season. Concentration of toxic and total alkaloids was measured by Fourier-transform infrared spectroscopy (FTIR), and alkaloid pools were calculated by multiplying the alkaloid concentration by the dry weight of the plant to express the amount of alkaloids in the stalk. Alkaloid pools in the stalks increased for the first three weeks, leveled off, then declined to very low levels as the plants began to senesce. We hypothesize that larkspur alkaloids are synthesized during the first 3-4 weeks of growth. Pools of alkaloids increase during this period, peak and level out from week 4-6, then the alkaloids appear to be catabolized or translocated. Concentration of alkaloids declined through the season as the alkaloids were diluted in the increasing biomass as the plants grew. These alkaloid patterns will be used to predict potential toxicity of larkspur populations.