POLYOL METABOLISM IN THE BASIDIOMYCETE SCHIZOPHYLLUM COMMUNE

Enzyme activities associated with arabitol and mannitol biosynthesis and catabolism in Schizophyllum commune

Enzymes of polyol metabolism were studied in basidiospore germination of Schizophyllum commune during periods of in vivo arabitol and mannitol pool depletion (growth on glucose-asparagine) and during their subsequent synthesis (growth on acetate-NH+4). Optimal conditions for assays were established and specific activities of enzymes employing D-arabitol, D-mannitol, D-ribulose, D-fructose and D-xylulose as substrates. were traced. Inquiries into the products formed during these reactions showed that D-ribulose generated arabitol while D-fructose produced mannitol with D-xylulose giving rise to xylitol. The dehydrogenase reactions were further investigated using polyacrylamide disc gel electrophoresis. Here was revealed the existence of at least two separate enzymatic activities pertaining to the catabolism of arabitol and mannitol. Also noted were the electrophoretic patterns when D-sorbitol, ribitol, xylitol and ethanol were used as substrates

Ultrastructural changes and biochemical events in basidiospore germination of Schizophyllum commune

Electron microscopic features and biochemical events were outlined in basidiospore germination of Schizophyllum commune. Normal ultrastructural changes included prominent vacuolization and more abundant endoplasmic reticulum. A lag phase in outgrowth included depletion of cellular reserves of trehalose, mannitol, and arabitol and subsequent increases in ribonucleic acid and protein. Depletion of polyols required exogenous carbon and nitrogen sources and was arrested by protein synthesis antagonists. Outgrowth subsequent to the lag period was accompanied by increased glycogen deposition and alkali-soluble glucan production.

Cytodifferentiation and morphogenesis in Schizophyllum commune

Images

Erythritol metabolism in wild-type and mutant strains of Schizophyllum commune

Erythritol uptake and metabolism were compared in wild-type mycelium and a dome morphological mutant of the wood-rotting mushroom Schizophyllum commune. Wild-type mycelium utilized glucose, certain hexitols, and pentitols including ribitol, as well as d-erythrose, erythritol, and glycerol as sole carbon sources for growth. The dome mutant utilized all of these compounds except d-erythrose and erythritol. Erythritol- or glycerol-grown wild-type mycelium incorporated erythritol into various cellular constituents, whereas glucose-grown cells lagged considerably before initiation of erythritol uptake. This acquisition was inhibited by cycloheximide. Dome mycelium showed behavior similar to wild-type in uptake of erythritol after growth on glucose or glycerol, except that erythritol was not further catabolized. Enzymes of carbohydrate metabolism were compared in cell extracts of glucose-cultured wild-type mycelium and dome. Enzymes of hexose monophosphate catabolism, nicotinamide adenine dinucleotide (NAD)-dependent sugar alcohol dehydrogenases, and reduced nicotinamide adenine dinucleotide phosphate (NADPH)-coupled erythrose reductase were demonstrated in both. The occurrence of erythrose reductase was unaffected by the nature of the growth carbon source, showed optimal activity at pH 7, and generated NAD phosphate and erythritol as products of the reaction. Glycerol-, d-erythrose-, or erythritol-grown wild-type mycelium contained an NAD-dependent erythritol dehydrogenase absent in glucose cells. Erythritol dehydrogenase activity was optimal at pH 8.8 and produced erythrulose during NAD reduction. Glycerol-growth of dome mycelium induced the erythritol uptake system, but a functional erythritol dehydrogenase could not be demonstrated. Neither wild-type nor dome mycelium produced erythritol dehydrogenase during growth on ribitol. Erythritol metabolism in wild-type cells of S. commune, therefore, involves an NADPH-dependent reduction of d-erythrose to produce erythritol, followed by induction of an NAD-coupled erythritol dehydrogenase to form erythrulose. A deficiency in erythritol dehydrogenase rather than permeability barriers explains why dome cannot employ erythritol as sole carbon source for mycelial growth.

Cellobiose as a paramorphogen in Schizophyllum commune

The mycelial growth of Schizophyllum commune on cellobiose, as sole carbon source, produced colonies that were quite dense and restricted in diameter. The hyphae were composed of shorter, more highly branched cells when grown on this disaccharide. Cellobiose brought about an increase in the ratio of an alkali-soluble cell-wall fraction (S-glucan) to an alkali-insoluble cell-wall fraction (R-glucan). This change might be explained by increased activity of enzymes which hydrolyze the R-glucan component following growth in cellobiose. Thus, a system is described which attempts to relate wall-softening enzymes to morphology.

Carbohydrate and Lipid Metabolism During Germination of Uredospores of Puccinia graminis tritici

Uredospores of Puccinia graminis (Pers.) tritici (Eriks. and Henn.) were uniformly labeled with (14)C by permitting the host (Triticum aestivum L.) to carry out photosynthesis in (14)CO(2) during the process of spore production by the obligate parasite. The use of (14)C labeled spores provided advantages in a study of the utilization of endogenous substrates at frequent intervals with small amounts of spores under conditions conducive to germination.Because of previous uncertainties about the nature of the substrates of importance to germination, a detailed study of carbohydrate and lipid components, both in the spores and in the germination medium, was made during the first 7 hours after placing the spores on aqueous media. Diethyl ether and 80% ethanol soluble metabolites each constituted approximately 20% of the total spore carbon. During the first hour nearly 60% of the 80% alcohol solubles disappeared from the spores while the total ether soluble material did not change appreciably. A significant part of the 80% ethanol soluble materials appeared in the germination medium.During germination and germ tube extension, there was rapid utilization of trehalose, arabitol and mannitol even though appreciable amounts of these materials were present as exogenous pools in the germination medium. Although the total amounts of ether soluble components did not change as drastically as the carbohydrate fraction, there was extensive utilization of palmitic, oleic, linolenic and 9,10-epoxyoctadecanoic acids.The results indicate that the germination process in spores of obligate parasites is not based solely on the utilization of lipids and some possible roles of the changes in internal and external pools of soluble carbohydrates are discussed.