Light microscopic and polypeptide analyses of sclerotia from mesophilic and psychrophilic pathogenic fungi

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Abstract
The structure and polypeptide composition of sclerotia of three mesophilic pathogenic fungi, Sclerotinia sclerotiorum, Sclerotium rolfsii, and Botrytis cinerea, and one psychrophilic snow mold, Myriosclerotinia borealis, were compared. The sclerotia of S. sclerotiorum and B. cinerea were black, round, hard structures which were composed of three areas: the rind, the cortex, and the medulla. Both the cortical and medullary areas of these sclerotia exhibited intensely stained inclusions. In contrast, sclerotia of M. borealis were not present as discrete entities but coalesced near the central point of inoculation. These black sclerotial masses were composed of thin-walled, pseudoparenchymal cells tightly packed together to form two distinct areas: a rind and a medullarylike region. No inclusions were evident in the medulla of cells of M. borealis sclerotia. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of sclerotial extracts of mesophilic fungi indicated the presence of major polypeptides. The polypeptide complement of B. cinerea contained a single, major polypeptide with an apparent molecular mass of 33 to 36 kDa. Similarly, sclerotia of S. sclerotiorum contained one major polypeptide of approximately 36 kDa in addition to one minor polypeptide of about 18 kDa. However, sclerotia of S. rolfsii contained a major polypeptide of about 16 kDa. Sclerotia of M. borealis contained a major polypeptide of 32 to 36 kDa and a minor polypeptide of about 16 kDa.

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