Regulation of lignin formation in reed canarygrass in relation to disease resistance

Lignin content and enzymes involved in lignification were measured in leaf discs of reed canarygrass (Phalaris arundinacea L.) inoculated with Helminthosporium avenae and floated on water or solutions of cycloheximide (25 mug/ml). Fungal germ tubes did not penetrate localized lignified swellings, which formed beneath penetration sites, in the outer epidermal wall of discs floated on water. Within 18 hours, inoculated discs on water had higher lignin content and higher activity of the enzymes phenylalanine ammonia lyase, tyrosine ammonia lyase, hydroxycinnamate-CoA ligase and peroxidase than noninoculated discs on water. When inoculated tissues were floated on cycloheximide solutions, increases in lignin content and enzyme activities associated with lignin biosynthesis were inhibited, and the tissue was susceptible to fungal penetration. Lignin biosynthesis at the site of attempted fungal penetration may play an important role in the resistant response of reed canarygrass to leaf-infecting fungi.