Membranous Structures in Yeasts

Abstract

Summary 1. Most yeast cells carrying out active respiration have spherical or ellipsoidal mitochondria, with plate‐like cristae. 2. Cytoplasmic petite strains of Saccharomyces cerevisiae have aberrant mitochondria, often containing whorled membranes. Mutants with deficiencies in the tricarboxylic acid cycle have mitochondria which appear normal when the cells are grown in low levels of glucose. 3. Cells of normal and petite S. cerevisiae grown strictly anaerobically show no recognizable mitochondrial profiles. 4. Carbon substrates which can only be respired promote the development of well‐defined mitochondria. In certain facultatively anaerobic yeasts respiration is suppressed by glucose and the mitochondria under these conditions are large, pleomorphic and few in number. Other fermentable carbohydrates do not give this repression. 5. A number of antibacterial antibiotics, which inhibit mitochondrial protein synthesis, cause a disorganization of the mitochondrial cristae. 6. In yeast cells adapting from anaerobic to aerobic conditions mitochondria appear to develop from proliferations of the endoplasmic reticulum, which become progressively more organized. 7. Vacuoles often contain granular material, but in S. cerevisiae the vacuole, which has been described as a lysosome, frequently contains myelin‐like lipid inclusions. The material in these inclusions is apparently derived from spherosomes. 8. Endoplasmic reticulum, orientated parallel to the plasmalemma, may be associated with fermentative ability in certain facultatively anaerobic yeasts. Endoplasmic reticulum is also actively involved in the budding process. 9. Normally the yeast‐cell plasmalemma shows only minor convolutions, but in chloramphenicol‐grown Rhodotorula glutinis the plasmalemma produces vesicular structures termed ‘paramural bodies’. 10. The yeast nuclear membrane has about 200 pores occupying 6–8 % of the total surface area. The nuclear membrane remains intact during mitotic division in yeasts until the daughter nuclei separate.

Lipids of yeasts.

“…Various membranous structures have been recognized (184) in yeast and have been assumed by Hunter and Rose (127) to contain the bulk of the cellular lipids. In general, unfractionated membranous systems possess a lipid:protein ratio of approximately 1 (88,163,176).…”

The Endoplasmic Reticulum as the Site of Potassium Tellurite Reduction in Yeasts

“…Melibiose, a non-repressing fermentable substrate, gave rise to membranes that preserved well (Marchant & Smith, 1968). The endoplasmic reticulum was less well-defined in S. cerevisiae 1-434 than in RhudutoruZa muciZaginosa 49 when fixed in permanganate, and was mainly oriented around the periphery of the cell inside the plasmalemma (PI.…”

Isolation of Cellulolytic Phycomycete Fungi from the Caecum of the Horse

“…This occurs in some yeast species such as Saccharomyces cerevisiae (Marchant & Smith, 1968), and some aquatic phycomycetes such as Aqualinderella fermentans (Emerson & Held, 1969) and Blastocladia SOD. (Emerson & Cantino, 1948;Held et aZ., 1969) which are obligately fermentative but not killed by exposure to oxygen.…”