Evaluating the Phototoxicity and Photogenotoxicity of Plant Secondary Compounds

Abstract

It is well known that the toxicity of many plant secondary metabolites is greatly enhanced in the presence of sunlight or UVA (320–400 nm). There are at least eight major biosynthetic classes of photo-activated chemicals which are distributed in many distinct families of higher plants (Table 1). Representative structures from each class are given in Fig. 1. It should be noted that some groups such as the polyines are quite large and include more than 500 known molecular structures which are distributed among the more than 10000 species of the largest plant family, the Asteraceae (reviewed in Towers 1984; Arnason et al. 1990). These phototoxins have been shown to be toxic to a wide variety of organisms including bacteria, fungi, viruses, insects, and mammals (Towers 1984). Although they have no known function in either plant physiology or metabolism, extensive studies in recent years have demonstrated their role as a defensive mechanism against attack by plant pathogens or insect herbivores.