ABSTRACT
Plant toxicants or secondary compounds are ingested along with other plant constituents. They act to deter feeding by herbivores although the mechanisms of deterrence are poorly understood. It is hypothesized that plant toxicants vary in the extent to which they are toxic and impose detoxification costs, and therefore could be classified along a continuum between the two. For example, alkaloids may be extremely toxic at doses which require trivial costs of detoxification, while terpenoids such as thymol or menthol are not particularly toxic but are contained in plants at concentrations which require substantial glucuronidation capacity and acid-base restabilization. The consequences of conjugation reactions are thus production of an acid load. It has been proposed that this represents a major metabolic cost to an animal and it is its ability to maintain acid base homeostasis in response to this acid load that determines the maximum intake of such compounds.
