THE EFFECT OF RADIATION UPON CELL RESPIRATION

Abstract

What seedlings were irradiated with X-rays and gamma rays in such doses as to impede growth by 40 per cent, as measured 24 hours after treatment. Various experimental conditions were maintained. The oxygen consumptions of the control and irradiated seedlings were determined at different intervals after irradiation, using the Barcroft-Warburg manometric method. Under all conditions investigated, except when the respiration was determined within 6 hours after irradiation, the results were the same—oxygen consumption per gram of growing tissue is not affected by doses of radiation sufficient to inhibit growth by as much as 40 per cent. Growth is inhibited before the respiratory rate changes. This is shown by the measurements made during the first 6 hours after irradiation, when the respiratory index is higher in the irradiated than in the control seedlings. This precludes a direct attack of radiation upon the respiratory mechanism. When growth is stopped by exposure of seedlings to 6° C., there is no observable difference in the respiratory rates of the control and irradiated seedlings, per seedling, even after 48 hours. This makes improbable any attack of radiation upon the respiratory mechanism itself. There is no observable change in the respiratory rate, per seedling, until the growth of the irradiated seedling lags behind that of the control; then the respiration per unit mass becomes the same in both. The eggs of Arbacia and Chœtopterus were given large doses of X-rays sufficient to hamper their early development, produce abnormal cleavages, and cause early death. The respiration of the irradiated eggs, measured by the Barcroft-Warburg method, was not affected by the doses of X-rays given. The increase in oxygen uptake under the influence of methylene blue was also unchanged by X-rays. The rate of increase in respiration of control and irradiated eggs, with time, is similar. Developmental anomalies appear before the respiratory rate is altered, and do not, therefore, depend upon respiratory impairment.