Release of Cell Wall Degrading Enzymes from Conidia of Blumeria graminis on Artificial Substrata.

Abstract

Cellulase and pectinase activities were examined in the exudates released from conidia of Blumeria graminis (Syn: Erysiphe graminis) and their germlings on two hydrophobic artificial substrata. Conidia were allowed to germinate on the substrata for 1, 6 and 16hr for the formation of primary germ tubes, appressorial germ tubes and maturation of appressoria, respectively. The exudates released by 16hr after inoculation were collected by washing the substrata with 10mM Tris-HCl buffer (pH 7.0). The exudate-buffer mixture was then charged on an anion- (High Q) and a cation- (High S) exchange column. Fractions eluted with a step-wise 0.2-1.0 NaCl gradient from a High Q column exhibited cellulase activity in a carboxylmethyl cellulose plate test and in ρ-nitrophenyl-β-D-cellobioside assay, but not pectinase activity in a polygalacturonic acid-yeast extract-agar plate test. Thus, cellulases are released from germlings by 16hr after incubation on the substrata. The exudates released at 1 and 6hr after inoculation also exhibited a little activity of cellulase but not of pectinase. However, the exudates from the surfaces of conidia on conidiophores which were prepared by washing with 10mM Tris-HCl buffer (pH 7.0) exhibited neither cellulase nor pectinase activities. The exudates prepared by washing conidia and germlings with 1M NaCl contained pectinase but not cellulase activities, suggesting that pectinases may be tightly adsorbed to the surface of the conidium. Homogenates of ungerminated conidia and germlings contained cellulase and pectinase activities, indicating that some of cellulase and pectinases are present constitutively within conidia. This is the first direct evidence that conidia of a powdery mildew fungus produce cellulases and pectinases and that their germlings release cellulases. Since carboxylmethyl cellulose and ρ-nitrophenyl-β-D-cellobioside were used as substrates to detect cellulase activity, the cellulases shown in this paper should be considered to correspond to carboxylmethyl cellulases and exo-β-glucanases.