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).