MORPHOLOGY AND LABORATORY CULTIVATION OF ECHINOSTELIUM MINUTUM

Alexopoulos , Constantine J. (State U. Iowa, Iowa City.) Morphology and laboratory cultivation of Echinostelium minutum. Amer. Jour. Bot. 47(1): 37—43. Illus. 1960.—The morphology of the sporangium, spores, swarm cells and Plasmodium of the white form of Echinostelium minutum is described. A peridium is present in the early stages of sporangial formation. It eventually disappears leaving only a small collar at the base of the columella. The structure of the spore wall is unique in this genus. The spore case may be described as consisting of a thin wall with several thickened portions distributed over its surface. These are particularly evident in germinated spores. Spore germination and swarm cells are described for the first time. Swarm cells are biflagellate with two long anterior flagella of nearly equal length. The Plasmodium remains microscopic until fruiting time, when it gives rise to but a single sporangium. The plasmodial protoplast never becomes differentiated into veins but remains more or less homogeneous. It exhibits almost imperceptibly slow, irregular streaming instead of the reversible, rapid, rhythmic motion characteristic of plasmodia of most other Myxomycetes which have been studied. It typifies, therefore, a third type of Plasmodium which may be placed alongside that of the Physarales, and that of Stemonitis flavogenita. The laboratory cultivation of E. minutum from spore to spore on agar media is reported here for the first time.     

THE LABORATORY CULTIVATION OF STEMONITIS

Alexopoulos , Constantine J. (State U. Iowa, Iowa City.) The laboratory cultivation of Stemonitis. Amer. Jour. Bot. 46(2): 140-142. Illus. 1959.—The cultivation of a species of Stemonitis, probably S. flavogenita, in laboratory culture is reported here for the first time. The organism completed its entire life cycle on artificial media from spore to spore, in the presence of contaminating bacteria, in 36 days. The plasmodium, characteristically different from those of the Physarales, is described and illustrated.     

Discrete steps in dioxygen activation—The cytochrome oxidase/O2 reaction

The kinetic constraints that are imposed on cytochrome oxidase in its dual function as the terminal oxidant in the respiratory process and as a redox-linked proton pump provide a unique opportunity to investigate the molecular details of biological O₂ activation. By using flow/flash techniques, it is possible to visualize individual steps in the O₂-binding and reduction process, and results from a number of spectroscopic investigations on the oxidation of reduced cytochrome oxidase by O₂ are now available. In this article, we use these results to synthesize a reaction mechanism for O₂ activation in the enzyme and to simulate time-concentration profiles for a number of intemediates that have been observed experimentally. Kinetic manifestation of the consequences of coupling exergonic electron transfer to endergonic proton translocation emerge from this analysis. Energetic efficiency in this process apparently requires that potentially toxic intermediate oxidation states of dioxygen accumulate to substantial concentration during the reduction reaction.