Single Cell Wall Research Articles

Demonstration by freeze-etching of a single cleavage plane in the cell wall of a gram-negative bacterium.

In the examination of protoplasts of a gram-negative bacterium classified as a Pseudomonas sp. by freeze-etching, we found a smooth external surface which is not seen if the preparations are not "etched." This external structure is seen as a sleeve surrounding and connecting the cells in unetched preparations, and we present evidence that it is a eutectic formed during the freezing of the specimen. In the system used in this study, the four layers of the cell wall of a gram-negative bacterium can be removed from the cell. The single cell wall cleavage plane is not affected by the removal of the loosely bound outer layer or of the peptidoglycan layer, but it is lost when the outer double track layer and the underlying soluble layer are simultaneously removed. Thus, we conclude that it is one of these two layers which is responsible for the cleavage plane which exposes variable areas of a smooth surface in the cell wall. This cell wall cleavage plane is more likely to deflect the actual cleavage of the frozen cell when cells are relatively old or when they are suspended in sucrose.

Hyphal structure in Fusarium oxysporum (Schlecht) revealed by freeze-etching.

Freeze-etched hyphae of F. oxysporum exhibited a single layered cell wall; a plasmalemma, in which invaginations were frequently associated with paramural vesicles; cytoplasma bearing lipid droplets, vacuoles, intravacuolar vesicles and nuclei with typical nuclear pores. Some hyphae bore crystalline inclusions characterized by a pronounced hexagonal, external ornamentation and it is suggested that the presence of these crystals and intravacuolar vesicles are indicative of aging hyphae.

On the effect of ultraviolet rays on the survival rate of the spores of various species of Aspergillus

Dry spores of 11 various mold species were irradiated with UV-rays. It was found that by irradiation with the same dosis the survival of the spores was very different and depended on the quantity of irradiating energy acting on a single spore. It seems that between the survival and the spore mass there exists a relationship, what is indicated by the sensibility index (Ef) which is the greater the less the survival. Probably the survival of the spores depended on its single or double cell wall.

Orientation of cellulose fibrils in the cell wall of growing cotton hairs and its bearing on the physiology of cell wall growth

Under certain conditions young cotton hairs, viewed between crossed nicols, falsely create the impression that transverse and spiral structures are present (Figs. 2, 3). This is caused by wrinkles in the shrunken cell wall, which are not oriented in spirals at all. The extinction angle of the birefringence in pieces of single cell wall protruding from cut ends of disintegrated young cotton hairs (Fig. 4) is almost transverse, which proves that the average fibril direction is either transverse or follows a very flat spiral, making an angle of less than 4° with the transverse. Electron micrographs (Figs. 5–8) show that the outer layer of the primary cell wall has an axial structure, while the inner layer has a more or less transverse structure. This is explained by passive extension of the outer part of the wall due to inadequate intussusception of fibrils therein. Into the inner part of the cell wall, however, new fibrils will be easily intussuscepted if the cell lengthens, permitting this part to retain a more or less transverse structure. The negative birefringence shows that this inner part is the predominating one.