Phytoalexin elicitor activity in carnation is associated with a neutral polysaccharide fraction of about 10 kDa and a glycoprotein isolated from the culture filtrates of Fusarium oxysporum f.sp. dianthi and Phytophthora parasitica Dastur, respectively. The molecular mass of the glycoprotein determined by MALDI experiments was found to be close to 25 kDa. The N-terminal region of this glycoprotein elicitor seems to be characteristic of the species parasitica and appears not essential for the phytoalexin-inducing activity. The glycosyl residue composition analyses of both active fungal compounds showed the presence of the same neutral sugars, mannose, galactose and glucose. Methylation analysis revealed that the active polysaccharides of F. oxysporum f.sp. dianthi correspond to the structurally complex branched hexopolysaccharides. A similar composition and distribution of the glycosyl residues in the sugar region of the active glycoconjugate of P. parasitica Dastur was observed, indicating a possible role of the polysaccharide moiety in the phytoalexin-inducing activity. The presence of hexofuranosyl residues was observed in extracellular polysaccharides of F. oxysporum f.sp. dianthi.
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