Two secretions from Botrytis cinerea important for pathogenesis
1996
Kamoen, O. (Rijkscentrum voor Landbouwkundig Onderzoek, Merelbeke (Belgium). Station voor Plantenziekten) | Cruyssen, G. van der
Numerous secretions from Botrytis cinerea have been described in the past. We examined two groups of secretions more closely, in relation to the expansion of lesions, viz. the polysaccharides (PSs) and the polygalacturonases (PGS). From B. cinerea we separated a dozen PGs by isoelectric focusing. One, PG.A is probably the most important, because it is the only enzyme present in the lesion border, while other PGs (PG.B and C) are present in the lesion center. PG.A is also secreted early, by the young hyphal tips during the germination of the conidia. At least two groups of polysaccharides may be distinguished, glucans (MW more than 500,000) and rhamno-galacto-gluco-mannans (rggMs) (MW more than 50,000). We found both groups in diseased grapes and strawberries. Infiltration of purified PG.A, or of partly purified rggM fractions into leaves induced similar symptoms to those observed at the lesion borders ahead of the hyphae. With purified PG.A, the first symptom was an inability of the host cells to plasmolyse, due to membrane damage. Disorganization of the cell content occured later, affecting particularly the chloroplasts. With purified rggMs however, firstly the chloroplasts degraded and only several hours later the cells lost their ability to plasmolyse. The rggMs containing 10 to 20 sugar molecules were most phytotoxic, the purified higher MW glucans were not phytotoxic. At low concentrations, the rggMs were elicitors of defence reactions. The expansion or restriction of the lesion depends mostly on the internal humidity of the plant tissue, suggesting a diffusion of the secretions ahead of the hyphae in the intercellular water films. Symptoms as caused by the rggMs are the first visible symptoms in vivo; and can be observed at a greater distance from the hyphal tips than the symptoms due to the PGs, suggesting that rggMs diffuse faster than PG.A, or at least are active at a greater distance.
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