Ultrastructure and lipid changes in Pyrenochaeta terrestris during aging.

Abstract

Pyrenochaeta terrestris, the onion pink root fungus, was grown on a reciprocal shaker in a synthetic medium which contained cellulose as the only carbon source. The mycelium was processed for lipid analysis and ultrastructural investigations after 8, 16, 24, and 32-day growth intervals.Hyphal cells contained membrane complexes. An electron-dense substance was present in large quantities on hyphal cell walls until after the 24-day period. As the cultures aged, organelles in some hyphal cells disintegrated and viable hyphal cells grew inside senescent cells in some cases. It was not possible to correlate positively lipid content observed at the ultrastructural level with the biochemical lipid analysis as a result of the relatively small amount of lipid observed in hyphal cells at the ultrastructural level.The lipid analysis indicated that the lipid content and mycelial weight reached a maximum at the 16-day period. The major fatty acids present were: C16:0, C18:0, C18:1, and C18:2. As aging occurred, the amount of unsaturation increased in the free fatty acids, the total fatty acids, and the fatty acids of the diglycerides and triglycerides. Only the fatty acids of the monoglycerides failed to increase in unsaturation. The sterol content increased slightly over the total growth period.