Two woody Rubiaceae species from tropical forest, Alibertia myrcifolia and Rudgea jasminoides, showed differences in relation to their capacity of producing phytoalexins, when challenged with fungi, and in the composition of the pectins from their cell walls. These species were compared in relation to the production and activity of phytoalexin-eliciting oligosaccharides derived from their leaf cell walls. Cell wall hydrolysis with Driselase showed that eliciting oligosaccharides were released from both species, although they are more easily obtained from Rudgea jasminoides, which presents positive phytoalexin response. Incubation of the cell walls with endopolygalacturonase promoted the production of oligosaccharides from R. jasminoides but not from Alibertia myrcifolia, which shows no phytoalexin response. Sequential hydrolyses with pectin-methylesterase and endopolygalacturonase that caused cell wall breakdown and release of eliciting molecules from A. myrcifolia, indicated the presence of pectins with different degrees of methylesterification between the two species. Additionally, oligosaccharides with low degree of polymerization (DP) were shown to inhibit phytoalexin response induced by a fungal elicitor or oligosaccharides with higher DP. These results suggest that the distinctive behavior between the Rubiaceae species in relation to phytoalexin production might be due to differences in the production of eliciting oligosaccharides from their cell walls as a consequence of the differences in the degree of the methylesterification and distribution of methyl-esters groups of their pectins.
methylesterification; monoclonal antibodies; oligosaccharides; pectin; phytoalexin
