Changes in mitochondrial structure of dimorphic cells of Endomycopsis fibuligera in saline medium.

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Since we first developed in 1964 to investigate electronmicroscopically the fine structure of an yeast,Endomycopsis fibuligera which behaves to grow in dimorphic type of the cell, namely yeast-like and filamentous ones, many papers concerned with the representations of the cell structure in comparison between two types of the cell. The purpose of the present investigation, therefore, is to clarify the significance of the effect of NaCl-hypertonicity on the structural changes in the grown cells in each type and the intracellular localization of NaCl taken up by the cells. An unique feature of grown cells in NaCl medium under shaking condition was a reminiscence of membrane system, resulted from the progressive degradation of mitochondria in growing cells. The difference of pronounced changes in mitochondrial degradation between yeast-like and filamentous cells indicated that the shape and the structure were differently linked to the cell metabolism in each type. This evidence has been approached by considering the comparative biogenesis of the irregular outline of vacuole in shape and the intravacuolar localization of NaCl taken up by the cell. The mitochondria can be identified both as a specific structural and a specific biochemical system, and current investigations aim at a more detailed understanding of the relationship between metabolic activity and structure. Halophytes and halophilic microorganisms must grow with high energy efficiency supplied by mitochondrial function to overcome the severe saline environment (Yabe et al. 1965, 1966). Conversely, although it has been obvious that slight but significant departures from a linear growth response of a non-halophilic yeast such asEndomycopsis fibuligera (formerly nomenclatured asE. fibuliger), under saline condition, must be taken into account of a specific ion effect in addition to the osmotic effect as so called dual effect, it will be expected that the progressive increase in cellular osmotic pressure with increasing salt concentration of external medium was directly and primarily related to the formation and the function of the mitochondria during decreased growth by added salt (Takada andKasakawa 1966 a, b). On the other hand, we have previously reported that when the cells ofEndomycopsis fibuligera were grown anaerobically, we could not found any mitochondrial structure within the cell and found concentrically arranged membrane system by means of electron microscopy (Hiraoka et al. 1966 b). There has been another experimental basis for believing that added NaCl or LiCl to hypertonic medium might to disintegrate the mitochondrial structure during growth, because this condition induced to enhance the anaerobic respiration associated with the depressed aerobic respiration accompanied with modified and different cytochrome pattern. A correlated ultrastructural study of mitochondrial structural states inEndomycopsis fibuligera has provided direct evidence of the effect of saline condition on mitochondrial morphologyin vivo.