Morphology and fine structure of the slime mold Dictyostelium discoideum

Abstract

The morphology of cell aggregates of the slime mold Dictyostelium discoideum at different stages of development have been investigated as ultrathin sections and studied by electron microscopy (Figs. 1–16). The investigations were concentrated on the mature sorocarp and especially on the sorophore and its sheath. The resistant framework in the sheath and the cell walls, from earlier work reported to contain cellulose, has been purified and extensively studied using a variety of methods—paper chromatography after hydrolysis, X-ray diffraction (Text-fig. 1), osmotic and viscometric measurements (Text-figs. 2 and 3), and fine structure analysis with electron microscopy after dispersion with ultrasonic waves (Figs. 17–21). From these investigations the following conclusions have been drawn concerning the sorophore sheath and the cell wall substance: The resistant fibrous substance, which is deposited extracellularly in the sheath and also occurs in the primary wall of sorophore and basal disk cells, is most probably—as isolated and purified here with hot aqueous 1 per cent sodium hydroxide—a partly mercerized cellulose of a very low crystalline order. The elementary fibrils or micelle strings of this cellulose are deposited in the sheath as layers with different orientation. When the substance is partially hydrolyzed, the fibrils are decomposed into rodlike fragments, micelles, of the same width as the original strings (~ 100 Å) but of lengths varying within wide limits.