Hyphal paramorphs of Ceratocystis adiposa (Butl)

Abstract

The aim of this project was to study the biochemical and cell wall changes involved during the induction of paramorphs of the ascomycete fungus Ceratocystis adiposa by sorbose and bile salts and to find how early these effects could be detected during the formation of a mycelium from spores. It was found that the reduction in radial growth rate (Kr) by sorbose was an osmotic effect. The rate of increase in dry weight with time was linear and not significantly reduced by the concentration of sorbose, glucose or polyethylene glycol which halved Kr; 0.25M. Botrytis fabae was sensitive to much lower concentrations of sorbose, Kr being halved at 0.01M sorbose and 1.0M glucose. The bile salt, sodium deoxycholate, caused a 50% reduction in Kr at 0.25 x 10 M without reducing specific growth rate In the paramorphs, Kr reduction was correlated with increased branch frequency. Electron micrographs of the cell wall showed no differences between the normal and restricted forms : the cell wall had three layers. The structure of the hyphae and especially of the septum was similar to that found in the human pathogen Sporothrix schenckii which has been proposed as an imperfect stage of Ceratocystis (Nicot and Mariat,1973) .Ungerminated and inhibited conidia showed the same cytoplasmic and cell wall structure reported by Hawes (1979). The cytoplasm contained many lipid droplets as energy reserves and these were not present in germinated conidia. Chemical analysis of the cell walls revealed that when Kr was reduced to 50% by O.25M sorbose and PEG 200, the glucan content of the cell walls was decreased. Glucose increased the glucan level while Na deoxycholate caused only a slight decrease. The only sugars found on hydrolysis of the cell wall fractions were glucose, mannose and N-acetyl glucosamine. Melanin in the cell wall prevented extensive enzyme dissolution. Only Na deoxycholate inhibited germination (50% at 7.5 x 10 M) although reversible inhibition occurred at concentrations of PEG which prevented growth (1.0M). When Na deoxycholate was used in glucose solution, the conidia seemed to swell and show nuclear division earlier than those incubated in SSM.* PEG = Polythylene glycol SSM = standard synthetic medium