Purification and partial characterization of a beta-glucan fragment that elicits phytoalexin accumulation in soybean.

The synthesis of phytoalexins (antibiotics) in plant cells is induced by molecules called elicitors. Partial acid hydrolysis of mycelial walls of Phytophthora megasperma f. sp. glycinea solubilized a multicomponent mixture of elicitor-active and elicitor-inactive oligoglucosides. One elicitor-active and seven elicitor-inactive hexa(beta-D-glucopyranosyl)-D-glucitols were purified by gel-filtration, normal-phase partition, and reversed-phase liquid chromatography after reduction with NaBH4. The elicitor-active and all but one of the elicitor-inactive hexa(beta-D-glucopyranosyl)-D-glucitols consisted of 3-, 6-, and 3,6-linked glucopyranosyl residues. The eighth hexa (beta-D-glucopyranosyl)-D-glucitol consisted of beta-4-linked glucopyranosyl residues. The similarity of the structural characteristics of six of the elicitor-inactive hexa(beta-D-glucopyranosyl)-D-glucitols to the elicitor-active hexa(beta-D-glucopyranosyl)-D-glucitol suggested that a highly specific carbohydrate structure was required for elicitor activity.