Prolonged carbohydrate starvation of sterile excised pea roots induces a stationary phase characterized by the accumulation of meristematic cells in either the G1 (90%) or G2 (10%) periods of the mitotic cycle which is relieved by carbohydrate supply. With the presence of carbohydrate, DNA synthesis and mitosis are resumed and the cells return to a normal mitotic cycle. In these experiments three groups of roots were irradiated with 300 R or 600 R of X-rays after: (1) 24 hours in the stationary phase, (2) 48 hours in the stationary phase, or (3) 24 hours in the stationary phase followed by another 24 hours in this phase before carbohydrate provision. Three cytological measurements were made: the increase with time in the number of${}^{3}{\rm H}\text{-thymidine-labeled}$ cells, the frequency of mitotic figures, and the appearance of${}^{3}{\rm H}\text{-thymidine-labeled}$ cells in mitosis. Cells in the first and second groups of roots displayed a delay in the increase of${}^{3}{\rm H}\text{-thymidine-labeled}$ cells, an initial reduction in division figures, and a delayed appearance of labeled mitotic figures. The recovery roots, however, displayed only a delayed appearance of labeled mitotic figures. Oxygen consumption measurements indicated the recovery of DNA synthesis, and the onset of cell division took place while metabolism was at a very low level. The overall results demonstrated that retardation of cell division enhanced the recovery rate of DNA synthesis and radiation-induced mitotic delay.

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