Chapter 8 



THE INDUCTION OF DORMANCY AND THE CONDITIONS FOR 



REACTIVATION 



DORMANCY 



Diploid cells which have been grown on presporulation agar for 

 a week or more (but have not yet sporulated) become filled with 

 mitochondria and glycogen (fig. 8-1), and as a result of these re- 

 serve accumulations are dormant. When tested in a Warburg ap- 

 paratus they are unable to give off CO2 or consume Oq. Accessory 

 substances are probably also involved in the induction of dormancy 

 since the presporulation medium is a very rich source of vitamins. 

 Dormancy can only be broken by presenting the dormant cells with 

 a nutrient containing vitamins and a nitrogen source in addition to 

 glucose sufficient to insure continued growth. Vegetative cells 

 which have grown on rich natural substrates, such as ripened fruits, 

 fill with reserves and may be similarly dormant. Dormant cells 

 either germinate from dormancy by a simple vegetative procedure 

 in an adequate medium, or the diploid dormant cells may sporulate 

 when placed on a gypsum slant along with a mass of other cells in 

 an acid (pH 4) milieu. In the latter case, conditions are unfavor- 

 able for continued vegetative growth just as they would be in a sandy 

 soil. These observations suggest that the vegetative cells grown on 

 ripe fruit become loaded with reserves and become dormant. K they 

 fall on another fruit or into a rich, sugary nutrient, they germinate 

 and grow vegetatively. At the end of the season when the fruits fin- 

 ally fall on the soil, sporulation occurs and the spores germinate 

 the following spring. 



It has long been known that yeasts store both fats and carbo- 

 hydrates, and the principal conditions controlling the storage of 

 these reserve materials have been fairly well worked out. It was 

 not known, however, that cells containing abundant accumulations 

 of reserve materials are in a state of dormancy; they are unable 

 to take up O2, to give off CO2, or to bud, either in a phosphate buf- 

 fer solution or in a buffer -glucose solution in the Warburg appara- 

 tus; but they begin to grow when they are brought into a complete 

 nutrient medium. The mechanism has a high survival value; it 

 prevents cells from "wasting" their reserves, since growth can 

 only begin under conditions in which continued or considerable 

 growth is possible. 



8-1 



