Elicitor-active components from French bean hypocotyls

Abstract

Components which induced phenylalanine ammonia-lyase activity and accumulation of isoflavonoid phytoalexins in cultured bean cells were obtained by fractionation of material released during autoclaving of bean hypocotyls and by hydrolysis of bean cell walls. Elicitor-active components from autoclaved hypocotyls were heterogeneous with respect to both charge and M r , and were found in fractions containing neutral sugars with no detectable protein or uronic acid as well as in fractions containing uronic acid as the sole carbohydrate. Elicitor activity was not destroyed by incubation of bean elicitors with sodium periodate, while treatment with proteinase K increased the elicitor activity of the autoclaved hypocotyl extract components. Pectic fragments produced by enzymic digestion of polygalacturonic acid with pectolyase, or by degradation into discrete oligomer fractions by autoclaving, appeared to be less potent as elicitors than the autoclaved hypocotyl extract components on a uronic acid basis. The optimal size for elicitor activity of oligogalacturonides was approximately nine galacturonosyl units. However, high concentrations of a mixture of oligomers obtained after hydrolysis of polymethylgalacturonic acid by autoclaving and removal of low M r material by dialysis elicited very high levels of phaseollin. No synergism was observed between autoclaved hypocotyl extract and fungal elicitor with respect to the induction of phenylalanine ammonia-lyase activity in cultured bean cells. The data suggest that the elicitor activity of the crude autoclaved hypocotyl extract resides in a complex mixture of pectic and other components.