Radiation Genetics in Wheat I

Chromosome aberrations in einkorn wheat induced by irradiation

抄録

1. Dormant seeds of Triticum monococcum L. var. vulgare Körn. were exposed to unfiltered X-ray irradiation, which was applied at 90 KVP, 3mA tube current and 15 cm distance for 12.5 to 62.5 minutes. The doses ranged from 2, 700 to 13, 500r units. The frequency of chromosome aberrations (mostly reciprocal translocation) in the P.M.C.'s increased in a parabolic relation to the dose (Table 1). The relatively small increase of the frequency at high doses is assumed to be partly due to limitations ascribed to the “saturation effect”.
2. At equal dose and target distance, with the increase of wave lengths of X-rays obtained by varying the kilovoltage and the time of exposure the aberration frequency decreases (Table 2).
3. If the two-hit aberrations are dependent upon two separate breaks, their new recombination is limited in time and space. The effect of varying the wave length was studied by keeping the dosage and the time of exposure constant and varying the target distance (Table 3). The result was a similar tendency in the relation of frequecy to wave length.
4. These facts could be explained on the basis of a difference in ionization distribution within the nuclei and chromosomes. In the case of hard X-rays much of the total ionization formed by the resulting electrons occurs relatively scattered in their tracks, whereas the ion pairs from soft X-rays are more closely spaced. Since at hard X-radiation chromosome breaks induced by the ionization are scattered in one chromosome or different chromosomes, the reunion of different broken ends, or interchange, occurs more easily than at short radiation with closely adjacent breaks, accompanied by much restitution.
5. In the induced chromosome aberrations in T. monococcum mostly (4)+5II, often 6II+2I and seldom (4)+1IV+3II or (6)+4II were observed, while in tetraploid plants losses of a whole chromosome and deficiencies or duplications of chromosome pieces were found, besides translocations. These results are attributed to the indispensability of at least one complete genome in haplo- and two complete genomes in diplophase, to secure viability in both phases.
6. By fast neutrons and γ-rays were such chromosome aberrations induced like those by X-radiation. The relation of aberration frequency to dose at these exposures was reported preliminary.