Evidence of two polygalacturonases produced by a mycorrhizal ericoid fungus during its saprophytic growth

Abstract

A mycorrhizal fungal strain (PS4), forming endomycorrhizae with the fine roots of ericaceous plants, was grown in pure culture on citrus pectin or sucrose as carbon source. Extracellular polygalacturonase (PG) activity was found only in the pectin-containing medium. Preparative isoelectric focusing identified two activity peaks (maximal activity at pH 4.2 and 5.7) that were attributed to two PGs (PG1 and PG2). Viscosimetric analysis revealed that PG1 hydrolyzes the substrate randomly, whereas PG2 shows an exo-mode of action. The pH optima were 4.6 for PG1 and 4.9 for PG2. The optimum temperature was about 55°C for both the enzymes. Both PG1 and PG@ degraded preferentially polygalacturonic acid and, to a lesser extent, citrus pectin. On Western blots PG1 was specifically labelled by a polyclonal antibody raised against an endopolygalacturonase from Fusarium moniliforme. The molecular mass of PG1, as revealed by the antibody, was 40 kDa. Labelling with Concanavalin A showed that PG1 is a glycoprotein. © 1993.