Biochemical changes during acetate deprivation and repletion in Euglena.

Summary Cultures of a streptomycin-bleached strain of Euglena gracilis, starved of acetate, remain almost completely viable for at least 13 days. Some biochemical effects of acetate deprivation and repletion in these cells have been examined. 1. The paramylon content decreases by 90 per cent during the 13-day acetate starvation, the RNA by 55 per cent, the protein by 45 per cent, and the DNA by about 30 per cent. The ability to oxidize added acetate decreases about 30-fold. The carotenoid content of these cells, however, increases. 2. The effect of the age distribution of cells in a logarithmically growing culture on these measurements was examined theoretically. It was suggested that the decrease in DNA could be accounted for by failure of the starved cells to resynthesize DNA after their last division. 3. Following the return of the starved cells to a complete medium there is a lag period of growth, linearly related to the length of starvation. In the first three hours of this lag period, before there is any appreciable protein synthesis, the ability to oxidize acetate increases greatly. At the end of the growth lag period logarithmic growth resumes with a normal generation time. The time course of biochemical resynthesis during this lag period depends upon the duration of starvation. 4. The data suggest the operation of control mechanisms allowing the cells to utilize cytoplasmic components selectively for survival.