Changes in phenolic acids content, phenylalanine ammonia-lyase and peroxidase activities in sugarcane leaves induced by elicitors isolated fromXanthomonas albilineans

Abstract

Xanthomonas albilineans is the agent responsible for a serious disease of sugarcane called leaf scald disease. Symptoms of the disease vary from a white line on the leaves to plant death. This paper correlates leaf scald resistance to changes in the concentration of phenolic compounds and phenylalanine ammonia-lyase and peroxidase activities in sugarcane leaves which were induced by a putative elicitor isolated from X. albilineans within different SE-chromatography fractions. The interaction was studied in leaf discs obtained from cultivars Louisiana 55-5 (susceptible to leaf scald) and Mayari 55-14 (resistant to leaf scald). SE-chromatography fractions containing only proteins enhanced the production of hydroxycinnamic acids (HCA) in cv. Mayari whereas fractions containing both proteins and carbohydrates enhanced the production of hydroxybenzoic acids (HBA) in cv. Louisiana. The eliciting protein(s) induced a level of PAL activity that increased the concentration of p-coumaric and caffeic acids, whereas ferulic acid, later synthesised in the host plant defence cycle, is used for the synthesis of syringic acid and for reinforcing the cell walls through peroxidase activation in the resistant cultivar. These facts justify the increase of p-coumaric, caffeic and syringic acids and the decrease of ferulic acid concentrations in this cultivar. Bacterial carbohydrates not only elicit the accumulation of p-coumaric acid, but also induce synthesis and accumulation of some hydroxybenzoic acids (HBA), such as gallic, protocatechuic and syringic acids and impede the production of antibacterial substances in the susceptible cultivar.