THE RELATIONSHIP OF M-INOSITOL TO MORPHOLOGY IN NEUROSPORA CRASSA

Shatkin , A. J., and E. L. Tatum . (The Rockefeller Institute, New York 21, New York.) The relationship of m-inositol to morphology in Neurospora crassa. Amer. Jour. Bot. 48(9): 760–771. Illus. 1961.—The role of m-inositol and its relationship to morphology in Neurospora crassa have been examined. The growth pattern of the inositolless mutant has been found to be a function of concentration of carbon and nitrogen sources and m-inositol, utilizability of carbon source, ratio of concentrations of sugar to m-inositol, and size of conidial inoculum. Inhibition of mycelial m-inositol uptake has been demonstrated for a number of carbon sources, and the ability of a particular compound to inhibit m-inositol uptake found to be directly related to both its effectiveness as an energy source and its effect on the morphology of the inositol-requirer. Results of cell-fractionation experiments and autoradiography have shown that phospholipid inositol is widely distributed in the hyphae and not bound in a single subcellular organelle. Electron micrographs of cell fractions indicate that inositol is a structural constituent of N. crassa lipoprotein membranes, including plasmalemma, nuclear envelope, mitchondrial membranes, and endoplasmic reticulum. Normal inositol-requiring and wild-type hyphae are similar in ultrastructure. However, sub-optimally cultured, colonial, inositolless hyphae contain large lipid droplets, and the cellular membranes are in various stages of degeneration. Chemical evidence indicates that colonial hyphae do not synthesize more fat than normal hyphae, suggesting that the lipid droplets are products of membrane catabolism. It is proposed that the colonial morphology of the inositol-requiring mutant of N. crassa is due to a metabolic imbalance between membrane synthesis and the synthesis of other cellular constituents.