antibiotic biosynthesis phytoalexin biosynthesis Biosynthesis of phytoalexins, a group of antibiotics produced by plants that are under attack. Phytoalexins tend to fall into several classes including terpenoids, glycosteroids and alkaloids. It is convenient to extend the definition to include all phytochemicals that are part of the plant's defensive arsenal. Phytoalexins produced in plants act as toxins to the attacking organism. pathway UPa:UPA00421 GO:0052315 plant chemical defense toxin biosynthesis antifungal biosynthesis