Phytoalexins, Chemical Defense Substances of Higher Plants?

Abstract

Abstract Phytoalexins are defense substances with antimicrobial properties which are produced by plants after infection. They include various groups of natural substances ( e.g. isoflavonoids, terpenoids, polyacetylenes and dihydrophenanthrenes). Induction of phytoalexin formation can be caused not only by living microorganisms but also by products of microbial origin (elicitors) or by stress treatment (cold, UV light). The elicitor from the mycelial walls of the fungus Phytophthora megasperma var. sojae (Pms) is a β‐1,3‐glucan with branches at C‐6. In some cases the basic features of the biosynthesis of the phytoalexins are known. The activity of the enzymes involved in phytoalexin biosynthesis is increased by the action of the elicitor on plant tissues. The ability of some microorganisms to chemically modify the phytoalexins may be related to their pathogenicity. The role of phytoalexins as defense substances is not yet fully clear.