6-13 THE YEAST CELL 



Henneberg (1926) and I (1945) have called them fat granules because 

 they are highly refractive; they coalesce when the cell is heated, or 

 dead, or treated with alcohol, and are conspicuous in cells whose 

 fat content is high. They are probably lipoidal coacervates with 

 ribosenucleoproteins. Caspersson suggested that the cytoplasmic 

 granules are the equivalents of both heterochromatin and the nucleo- 

 lus, since heterochromatin is associated in higher forms with the 

 production of ribose nucleoproteins. However, a true nucleolus is 

 present in the vacuole and I consider the Feulgen -positive bodies in 

 in the centrosome the equivalents of heterochromatin. 



I (1948) have identified the cytoplasmic granules with mitochon- 

 dria. They disappear when the cell is treated with acetic acid, which 

 would not be expected if they contained only ribose nucleoprotein, 

 but is characteristic of mitochondria. They coalesce when the cell 

 is heated, or treated with alcohol, or subjected to pressure, which 

 is also consistent with the view that they contain lipoids or fats. 

 They increase while fat storage occurs and are abundant in cells 

 containing large amounts of fat. Precise information on their re- 

 action to fat stains is difficult to obtain, because most fat stains 

 enter the living cell only slowly or not at all. The surroimding cyto- 

 plasm contains considerable amounts of fat, so that fat stains quick- 

 ly overstain the entire cell. In dead cells the structure is so changed 

 that localization of fat may easily lead to false conclusions concern- 

 ing its actual disposition in the living cell. Caspersson and Brandt 

 pointed out that the granules (mitochondria) show an irregular bound- 

 ary with the ultraviolet microscope. With the Spencer phase -differ- 

 ence lens that I have been using, the boundary between the cytoplasm 

 and the mitochondrium is very distinct (fig. 5-1). These facts sug- 

 gest that the mitochondria are lipoidal or fatty bodies containing ri- 

 bose nucleoprotein. Caspersson and Brandt found optically empty 

 fat vacuoles in the cytoplasm in certain old cells. These can easily 

 be produced by heating or merely drying and fixing yeast containing 

 a large number of mitochondria on a slide in the usual manner. 

 They state that the optically empty bodies are probably the fat gran- 

 ules described by Henneberg, but Henneberg' s figures show clearly 

 that he meant the smaller granules in the cytoplasm when he spoke 

 of "fat granules." Figs. 6-8 to 6-11 show mitochondria in various 

 types of cells. 



There seems to be a relation between the mitochondria and the 

 centrosome. The last mitochondria to disappear when budding be- 

 gins are those at the base of the centrosome (fig. 6-8). Mitochon- 

 dria often form a mantle surroimding the centrosome. These facts 

 suggest that the mitochondrial ribosenucleoproteins may be synthe- 

 sized from the centrosomal Feulgen -positive heterochromatin. Cas- 

 persson and Schultz (1940) and Schultz, Caspersson and Aquilonius 



