Ultrastructural localization of β-1,4-glucan-containing molecules in the cell walls of some fungi: a comparative study between spore and mycelium

An exoglucanase, purified from a cellulase produced by the fungus Trichoderma harzianum was complexed to colloidal gold and used for localizing β-1,4-glucan-containing molecules in the cell walls of some fungi. With the exception of Aspergillus niger, β-1,4-glucan-rich molecules were found to be associated with conidial walls of Trichoderma viride, Fusarium oxysporum f.sp. radicis-lycopersici, Verticillium albo-atrum, Penicillium thomii, and Ophiostoma ulmi. The abolition of wall labeling following previous cellulase digestion suggested that the compunds detected by the exoglucanase–gold complex were likely of cellulosic nature. Differences in cell wall composition between conidia and mycelium were reflected by the absence of β-1,4-glucan-containing molecules in the vegetative walls of most fungi tested. This raises the question as to what extent the chemical composition of spore walls should be considered as an important criterion in the taxonomy and phylogeny of fungi. The disappearance of these molecules upon conidial germination (with the exception of O. ulmi) suggests that lytic enzymes are produced to cause wall breakdown. The presence of molecules with β-1,4-linkages in conidia probably contribute to reinforcement of the wall architecture. Key words: fungi, spores, β-1,4-glucan, gold cytochemistry.