Phytochemistry

Abstract

Compared to many other angiosperms, the grasses are not noted for the diversity of their secondary compounds. However, as indicated below, this may simply reflect lack of investigation. A wide range of secondary compounds is reported, but in general the data come from a handful of taxa that are particularly important for grazing or field crops; the taxonomic distribution of most compounds is thus largely unknown. Secondary compounds may be produced by roots or by above ground tissue, and production may be constitutive, or be triggered by herbivore attack, or be produced in response to the presence of particular bacteria or fungi. Of the 2400 species in a database of plants with pest-control properties (Grainge and Ahmed 1988), about 50 are grasses; documentation of the chemicals produced by these plants and their effects on other organisms varies considerably in quality. Compounds produced in response to pathogens are sometimes called phytoalexins, a term that refers to their inducibility rather than their chemical composition. A number of grass species harbor fungal endophytes that produce secondary compounds that serve as plant defense; in this case the defense compound is in fact a product of the fungus rather than the plant. Finally, cell walls in the grasses have a distinctive chemical composition; whether it is adaptive in any way is unknown. The material presented here is not intended to be a comprehensive review, but will provide some hint of the phytochemical diversity to be explored in the family.