Histochemistry and storage of organic compounds during basidiosporogenesis in the ectomycorrhizal fungus Pisolithus microcarpus

Knowledge on the distribution and storage of different organic compounds during basidiosporogenesis in P. microcarpus is paramount to a better understanding of basidiospore recalcitrance to germination. The objective of this work was to detect the presence and distribution of phenolics, reducing sugars, starch, glycogen, total polysaccharides, RNA, and proteins during P. microcarpus basidiosporogenesis. Starch and reducing sugars were not detected in the fungal basidiocarps, while other polysaccharides predominated in the extracellular matrix at the base of the basidiocarp containing unconsolidated peridioles. Phenolics were also detected in this region. Glycogen was present inside the hyphae, basidia, and basidiospores and constitutes an important storage compound in the fungal basidiocarps. In mature basidiospores, RNA accumulation occurred at discrete locations in the cytoplasmatic periphery, while polysaccharides and proteins were shown to predominate in the cell wall. The presence of glycogen, RNA, and proteins inside the basidiospores strongly indicates provision for future germination and suggests that other factors may also influence basidiospore recalcitrance.