Studies on Isaria cretacea. Morphogenesis of the synnema and endogenous nutrition.

Abstract

The indeterminate-growing synnema of Isaria cretacea arises from the vegetative mat when it is grown on No. IS-M synthetic medium. Synnemata development is not dependent upon the particular carbon or nitrogen source, or on the concentration of carbon, nitrogen, or phosphate of this medium. Development does require more exogenous biotin and thiamine than is required for maximal vegetative mat growth. Sucrose is a specific inhibitor of synnemata development and when it replaces the glucose of the medium the mat grows more profusely, the pH drops further, and synnemata do not appear. Addition of indoleacetic acid, which inhibits endogenous respiration of I. cretacca, to the sucrose medium retards vegetative mat growth (primary vegetative growth) and initiates synnemata growth (secondary vegetative growth). Addition of calcium carbonate or phosphate buffer also results in the development of synnemata but does not retard vegetative mat growth. It was concluded that the synnema is the product of the change of the center of growth from the hyphal tips of the vegetative mat to the hyphal tips of privileged vertical hyphae. Efficient translocation and a potentiality for indeterminate growth would seem to be requirements for synnemata morphogenesis. Secondary growth ordinarily follows primary growth but the sequence can be interrupted if an exogenous nutrient favors either continued primary growth or rapid staling of the medium. The data suggested that the synnema was synthesized from endogenous nutrients and this conclusion was supported by the observation that synnemata readily developed from washed mycelium that had been placed in a nutrient-free moist chamber.