Multivesicular Bodies in Sclerotinia Fructigena and their Possible Relation to Extracellular Enzyme Secretion

Summary: The occurrence of multivesicular bodies (m.v. bodies) in Sclerotinia fructi-gena, both in vivo and in vitro, was studied by electron microscopy. This investigation was an attempt to correlate the existence of m.v. bodies with extracellular enzyme production. It was observed that when the fungus grew in its natural hosts or in media containing pectin or sodium pectate, where extracellular pectolytic enzyme secretion was high, m.v. bodies were present in the hyphae. However, when the fungus grew in synthetic media without pectin or sodium pectate, these m.v. bodies were absent, and the extracellular enzyme activity was very low. Multivesicular bodies in S.fructigena seemed to originate from the endoplasmic reticulum, moving later to the periphery of the cell. A new histochemical technique was used at the electron microscope level; this provided supporting evidence that m.v. bodies are the cytoplasmic constituents involved in extracellular enzyme secretion by this fungus.