Brementown Revisited: Interactions Among Allelochemicals in Plants

Abstract

While certain individual plant chemicals are closely identified with particular plant families—sinigrin and the Cruciferae, for example¹—plant species in reality produce. a variety of biosynthetically distinct secondary compounds. The tremendous chemical diversity that characterizes the angiosperms in general holds for an individual plant as well. The Umbelliferae are among the more diverse; even the rather undistinguished parsnip (Pastinaca sativa), a biennial that is a minor vegetable crop under cultivation and a noxious weed when naturalized, contains no fewer than seven classes of secondary compounds (Table 1). Yet interactions among co-occurring secondary compounds as regards herbivory, insect and otherwise, have been largely ignored by investigators who have instead concentrated on single classes of secondary products. This emphasis is the result of both practical and theoretical considerations. Operationally, examining a single class of compounds facilitates the design and execution of experiments. Conceptually, stepwise insect/plant coevolution, as formalized by Ehrlich and Raven,² derived largely from experimental work on the Cruciferae;^3–5 the dramatic effects of mustard oil glycosides as toxins to nonadapted species^6,7 and as attractants to adapted species^8–12 led to the tacit assumption (and fervent hope) that single chemicals can provide the key to understanding insect/plant relationships.

“When we are all performing together it will have a very good effect.” The ass, in “The Brementown Musicians”

(J. and W. Grimm, 1814)