Biological activity of defence-related plant secondary metabolites

Althought is accepted that secondary metabolites and natural products in plants are involved in diverse activities, the function of most of the thousands of phenolics, quinones, terpenes, flavonoids and other low molecular weight meta-bolites remains unknown. The best understood secondary metabolites are implicated in defence against pathogens, with the mode of action of some of these established. Interestingly, to date, a relatively small number of processes have been shown to be the targets of plant metabolites and these include electron transport chains, mitochondrial function and membrane integrity. It is now emerging, however, that other specific enzymes and processes may also be the targets of particular metabolites. There is a general hope that modern genomic approaches will identify new targets and modes of action of plant metabolites. Molecules, especially triterpenoids, that trigger apoptosis or autophagy in tumour cells are of particular interest in this regard. When considering the approaches taken in plant science hitherto, and the strategies that have yielded success in the biomedical -sector, we discuss whether there is a case to be made for carrying out initial studies on mode of action in a genetically tractable system like the yeast Saccharomyces cerevisiae, before moving to specific studies in plant or human cells.