CHLOROPLAST ABERRATIONS IN IRRADIATED FERN SPORES

Aberrations affecting chlorophyll and/or chloroplasts were scored amongst the survivors of irradiated haploid spores of the fern Osmunda regalis. They were classed in 8 recognizable groups, which occurred in the same relative numbers in irradiated and control samples. Two distinct types, comprising respectively 4.7% and 1.6% of all the aberrations, gave evidence of being due to mutation of nuclear genes. All the aberrations exhibited a high degree of somatic stability. The frequency of occurrence of aberrations was closely correlated with the rate of cell killing in all experiments. Factors which modified the effectiveness of the radiation in killing spores always modified to a similar extent its effectiveness in producing aberration amongst the survivors. These factors included LET of the radiation, the physiological state of the spores at the time of irradiation, whether the radiation dose was given at a single exposure or in two fractions, and the presence of oxygen during irradiation. In unirradiated spores the aberration rate increased markedly with length of time in storage. © 1968.