A survey of biochemical changes which follow the irradiation of potato tubers in the lower decakilorad range has revealed that the following increase above those of unirradiated controls: (a) sugars, especially sucrose; (b) inorganic phosphate; (c) apparent nucleic acid content of ammonium sulfate-precipitable fraction; (d) lactic dehydrogenase activity of soluble protein fraction; (e) polyphenol oxidase induced chromogenicity of freshly sliced tuber surfaces. The following were found to decrease: (a) the rate of sprout growth; (b) resistance to microbial attacks; (c) apparent protein content of ammonium sulfate-precipitable fraction.
There was little or no consistent effect on the pH of freshly prepared crude extracts nor on the inhibition by adenosine triphosphate of the above-mentioned chromogenicity. Ascorbic acid rose immediately after irradiation but decreased to control levels within 1 day. The level of the phosphorylase with respect to controls depended upon the post-irradiation temperature. The magnitude, duration, and, in some instances, the directions of these effects were found to be dependent upon the pre- and postirradiation history of the tubers as well as on the irradiation dosage. The radiobiological basis for some of these effects is discussed. The apparent postirradiation increase in some enzyme-linked reactions has been interpreted tentatively in terms of a hypothesis involving the possible differential radiosensitivity of the mechanism for synthesis of individual enzyme proteins as compared with the sensitivity of the mechanism for their degradation.