Transfer of quinolizidine alkaloids from hosts to hemiparasites in two Castilleja-Lupinus associations: analysis of floral and vegetative tissues

Many hemiparasites, including several members of the Castilleja genus (Scro phulariaceae), obtain secondary compounds from their host plants, Both Cast illeja miniata in subalpine Colorado and C. indivisa in central Texas have reduced herbivory when obtaining alkaloids from the hosts Lupinus argenteus and L. texensis (Fabaceae), respectively. However, pollinators were not de terred from visiting Castilleja parasitizing alkaloid-containing hosts. To determine if alkaloids are present in all tissues of plants parasitizing lu pins, we analyzed floral tissue as well as leaves of both Castilleja specie s. Leaves, bracts, calices, corollas, gynoecium and nectar of both Castille ja species were examined for quinolizidine alkaloid presence using a Dragen dorff reagent, and alkaloids were identified in vegetative tissue and necta r by capillary GLC and GLC-MS. Lupanine and alpha-isolupanine were the prin cipal alkaloids in C. indivisa parasitizing L. texensis, while principal al kaloids of C. miniata parasitizing L. argenteus were 5,6-iso-dehydrolupanin e, alpha-isolupanine, thermopsine, and 17-oxolupanine. Except for 17-oxolup anine, which was probably synthesized by biotransformation in the parasite, all other alkaloids correspond to those present in the host plants. Alkalo ids were present in the leaves of both Castilleja species, and in the bract s, calices and gynoecium of some plants, but never in the corollas. Alkaloi ds from L. texensis and L. argenteus were not detected in nectar of either Castelleja species. The presence of alkaloids leaves and outer floral tissu e of both Castilleja species, but not nectar. may explain why alkaloid upta ke and storage affected herbivores but not pollinators. (C) 2001 Elsevier S cience Ltd. All rights reserved.