Alvin V. Beatty

Radiation repair of chromosome breaks as effected by constituents of nucleic acids

Abstract In these experiments with a total dose of 400 R of X-rays in a helium atmosphere, Tradescantia inflorescences treated in adenine, guanine, cytosine, uracil, thymidine, adenosine, adenosine 2′-, 3′-, and 5′-monophosphates, adenosine-5′-diphosphate, deoxyadenosine-5′-mono- and 5′-triphosphate did not show an average aberration frequency differing from that of the control in helium. Thymine, guanosine, cytidine, uridine, guanosine triphosphate, thymidine triphosphate and uridine triphosphate treatments reduced the aberration yield by approximately 25 per cent. Adenosine triphosphate, cytidine triphosphate, deoxyadenosine, deoxyguanosine, deoxycytidine, deoxyuridine and 3′–5′-diphosphoadenosine effected approximately a 50 per cent reduction in aberration yield. We do not believe the compounds which bring about a reduction in aberration yield do so by reducing the amount of initial radiation damage. We believe that some compounds such as the triphosphates may be reducing aberrations by furnishing energy to the cell. These compounds, as well as the deoxy compounds and 3′−, 5′-diphosphoadenosine, may also be involved directly in the chemical repair of the radiation-induced breaks.

Metabolic repair of radiation-induced chromosomal damage

Abstract Chromosomal aberrations of the exchange types induced in the microspores of Tradescantia with 400 r of X-radiation delivered at 50 r/min in a helium atmosphere are used as a measure of radiation damage. Materials treated with potassium gluconate, ATP and glutathione either before or after irradiation showed approximately 40 per cent fewer aberrations than the irradiated controls. Neither doubling the concentrations of chemicals nor increasing the time of treatment gave any further reduction in aberrations. Three experimental temperatures were used with each chemical. The lowest, 0·2°C, when used alone, reduced aberrations to the same extent as the chemicals at 30°C. Any two of the four variables gave some synergistic effect, which was not increased by using all four at one time. In addition to these chemicals, glucose 6-phosphate, 6-phosphogluconate, TPNH, DPNH and others also proved effective, indicating that the energy for recovery was being obtained through the hexose monophosphate shunt.

Chromosomal aberration gradients in Tradescantia anthers

Abstract Inflorescences were X-irradiated for one minute at 400 r/min in atmospheres of helium, 100 per cent oxygen, 5 per cent oxygen with 95 per cent helium or with 95 per cent CO, and 20 per cent oxygen with 80 per cent helium or with 80 per cent CO, fixed 96 hr later in Craf fixative, then sectioned and stained in crystal violet. After the sections were projected and traced, cells in metaphase of the first microscore division were identified, their position in the cross-section of the anther marked, examined subsequently under oil immersion for chromosomal aberrations of the ring and dicentric types and recorded as aberrations occurring in the outer or inner regions of the tissue. Materials irradiated in the various gases gave aberration yields per cell, in outer and inner regions respectively, of: 0·74 and 0·44 in 5 per cent oxygen, 0·85 and 0·61 in 20 per cent oxygen, 0·28 and 0·26 in helium, and 0·96 and 0·86 in 100 per cent oxygen. Material irradiated in the 5 per cent oxygen-helium mixture, then post-treated in CO, gave yields of 0·64 and 0·66, while the same treatment in 20 per cent oxygen-helium mixture gave 0·82 and 0·80. The aberration gradients found in the first two experiments reported here are interpreted on a metabolic gradient basis, which would influence recovery, rather than on an oxygen gradient in the tissue during irradiation, which would modify breakage.