SEASONAL and INTRAPLANT VARIATION of CARDENOLIDE CONTENT in the CALIFORNIA MILKWEED, Asclepias Eriocarpa, and IMPLICATIONS for PLANT DEFENSE 1
Journal of Chemical Ecology, VoL 7, No. 6, 1981 SEASONAL AND INTRAPLANT VARIATION OF CARDENOLIDE CONTENT IN THE CALIFORNIA MILKWEED, Asclepias eriocarpa, AND IMPLICATIONS FOR PLANT DEFENSE 1 C.J. NELSONY J.N. SEIBER, 2 and L.P. BROWER 3,1 2Department of Environmental Toxicology University of California, Davis, California 95616 3Department of Zoology, University of Florida, Gainesville, Florida 32611 (Received October 31, 1980; revised January 19, 1981) Abstract--Root, stem, leaf, and latex samples of Asclepias eriocarpa collected from three plots in one population at 12 monthly intervals were assayed for total cardenolide content by spectroassay and for individual cardenolides by thin-layer chromatography. From May to September mean milligram equivalents of digitoxin per gram of dried plant were: latices, 56.8 >~ stems, 6.12 ~ leaves, 4.0 > roots, 2.5. With the exception of the roots, significant changes in gross cardenolide content occurred for each sample type with time of collection during the growing season, whereas variation within this population was found to be small. Labriformin, a nitrogen- containing cardenolide of low polarity, predominated in the latices. Leaf samples contained labriformin, labriformidin, desglucosyrioside, and other unidentified cardenolides. In addition to most of the same cardenolides as the leaves, the stems also contained uzarigenin. The roots contained desglucosyrioside and several polar cardenolides. The results are compared with those for other cardenolide-containingplants, and discussed in relation to anti-herbivore defense based on plant cardcnolide content. Arguments are advanced for a central role of the latex in cardenolide storage and deployment which maximizes the defensive qualities of the cardenolides while preventing toxicity to the plant.
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