Probabile aumento transiente della demolizione di RNA durante il periodo successive all’aggiunta di ammonia a cellule di Rhodotorula gracilis coltivale in presenza di nitrato

The growth rate of cells of Rhodotorula gracilis in liquid mineral medium is the same whether nitrogen is supplied as ammonia or as nitrate, though the pH in the culture medium becomes stabilised around 2.5 and 6.6 respectively. Growth was measured as increase in fresh weight, in dry weight and in protein. Under the two conditions mentioned, no difference was found in the RNA and aminoacids levels, on a fresh weight basis. The addition of ammonia to cells growing in the presence of nitrate causes, within the first hour of incubation, a decrease in the growth rate (measured as the increase in fresh weight, dry weight and protein) as well as a block in the accumulation of RNA. During this per:.od, transcription does not seem to be affected: labeling experiments show that the capacity to incorporate 32p is not altered by the addition of ammonia. The block in the accumulation of RNA appears to be dependent upon the breakdown of the RNA already present in the cells.