A freeze-fracture study of hormone-induced branching in the fungus Achlya.

The induction of the male sexual organ primordia (antheridial hyphae) by the steriod hormone antheridiol in the water mold Achlya ambisexualis Raper requires the production and secretion of the enzyme cellulase. It is postulated that a localized secretion of cellulase produces a limited area of wall hydrolysis that is blown out into a lateral bleb by turgor pressure. Freeze-etch preparations show membrane profiles similar to those seen in other systems where exocytosis is occurring. Such a mechanism would provide the required localized secretion of cellulase. Water stress, imposed by polyethylene glycol, prevents the formation of antheridial hyphae, the secretion of cellulase and the expected membrane profiles. After a period of recovery from water stress antheridial hyphae are formed, cellulase secretion occurs and the expected membrane profiles are restored.