ABSTRACT
Plants produce several secondary metabolites that are distinct from the components of
intermediary (primary) metabolism, in that they are generally nonessential for the basic
metabolic processes of the plant (Dixon, 2001). Most of the secondary metabolites show
antifungal action. There are two types of antifungal secondary metabolites: phytoalexins
(inducible secondary metabolites) and phytoanticipins (constitutive secondary metabolites)
(VanEtten et al., 1994). Phytoalexins are defined as the compounds that are synthesized
denovo in response to infection, accumulating to antimicrobial concentrations in the area
of infection (Dixon and Harrison, 1990; VanEtten et al., 1995), whereas phytoanticipins are
defined as the compounds that are preformed infectional inhibitors (VanEtten et al., 1994).
However, sometimes it is difficult to differentiate phytoalexin from phytoanticipin based on
these definitions. Some compounds may be phytoalexins in one plant species and phytoanti-
cipins in others. For example, sakuranetin is inducible in rice leaves, but accumulates
constitutively in leaf glands of blackcurrant (Kodama et al., 1988). Some phytoanticipins
may be produced in larger amounts after infection. If their constitutive concentrations were
sufficient to be antimicrobial, they are called phytoanticipins, otherwise they should be called
phytoalexins (Dixon, 2001).