The primary objective of this study was to investigate the radiosensitivity of Pseudotsuga menziesli (Mirb.) Franco, Douglas-fir, from two different provenances representing the coastal and interior regions in British Columbia, Picea sitchensls (Bong.) Carr., Sitka spruce, and Tsuga heterophylla (Raf.) Sarg., Western hemlock. A secondary objective was to correlate the radiosensitivity with some cytogenetical and biochemical characteristics. Induction of mutations and radiostimulation of seed germination and seedling growth were also sought. Filled seeds of the above mentioned species were given five different dosages of gamma-irradiation from a cobalt-60-source control, 500, 2,000, 5,000, and 10,000 R. Stratification for 14 days at 0°-2°C as post-irradiation treatment was tested. Germination values were evaluated and germinants were transplanted. Survival and growth under controlled environmental conditions were recorded for 182 days. The species exhibited differential responses to seed irradiation. All showed drastic reduction in germination and survival at the higher dosages, (5,000-10,000 R). There was some stimulation of Interior Douglas-fir seed germination and seedling survival at 500 and 2,000 R irradiation dosages over the control. The same exposures stimulated the height growth of Coastal Douglas-Fir. Stratification after irradiation reduced seed germination and seedling growth and survival in all the species. The tolerance to gamma-irradiation decreased in the following Order: Interior Douglas-fir, Coastal Douglas-fir, Western hemlock and Sitka spruce. Sitka spruce had a significantly larger nuclear volume than Western hemlock and Douglas-fir. No correlation was found between nuclear volume, or interphase chromosome volume, and LD₅₀ (germination). The amount of DNA per cell and per chromosome differed significantly among the three species with Sitka spruce having the highest DNA content followed by Western hemlock, Coastal Douglas-fir and Interior Douglas-fir. Significant negative correlations were found between DNA content per cell and per chromosome, and LD₅₀ (germination). This indicated that DNA content plays a more important role than nuclear volume in determining the radiosensitivity of the species. The differences in radiosensitivity, nuclear volume and DNA content between the Coastal and Interior forms of Douglas-fir are discussed in relation to their ecogeographical distribution and taxonomy. Chromosome breaks, micro-nuclei and chromosome erosion were detected in irradiated seeds of Douglas-fir. Intraspecific hybridization was carried out in Douglas-fir using gamma-irradiated pollen grains. Pollen irradiation up to 5,000 R increased the number of filled seeds/cone. Seedlings from pollen irradiated at 500 R, exhibited some increase in height growth. Similar effects were obtained for pollen germination in vitro. The possibilities of utilizing seed and pollen irradiation in forest tree improvement are discussed' and recommendations are made for future mutation breeding work. / Forestry, Faculty of / Graduate

The experiments reported in the present dissertation were undertaken to obtain further evidence for the possible roles of protein, RNA and DNA macromolecules in radiation-mutagenesis in Drosophila melanogaster. Several antibiotics were tested for their modifying effects on the frequency of radiation-induced sex-linked recessive lethals. Pre-radiation treatment with actinomycin D significantly reduces the frequency of induced mutations in germ cell stages assumed to include spermatids and spermatocytes. These results are consistent with the hypothesis of a role of proteins in the stabilization (repair) of radiation-induced premutational lesions. Puromycin, a specific inhibitor of protein synthesis is ineffective in the modification of induced mutation frequencies in Drosophila melanogaster. Mitomycin C, is itself a potent mutagen in all germ cell stages, peak mutagenicity occurring in spermatid stages. In combination with ɣ-rays, mitomycin C shows an overall additivity of effect. Mutation frequencies due to mitomycin C are not altered by pre- or concurrent treatment with actinomycin D. This may indicate a different mechanism for mutagenesis by mitomycin C and radiation. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

The ICRP recommends a radiation weighting factor of one for all low-LET radiation. However, many experimental studies find inconsistencies between low-LET RBE and the ICRP's current radiation weighting factor. Generally, there is evidence that dependence exists between radiation energy and radiation RBE where lower energy radiations tend to have a greater biological effect than higher energy radiation. Specifically, the radiations of tritium and carbon K-shell x-rays have been studied in numerous experiments and the biological effects of both of these radiations are consistently greater than that of Co-60. In this work, the relationship between radiation energy and radiation effect has been investigated with the use of a newly developed double strand break (DSB) yield estimation algorithm. This algorithm makes use of a detailed solenoidal 30 nm DNA chromatin model to describe the radiation-sensitive biological target. In addition to the DNA model, NOREC, an event by event Monte Carlo code, was used in this algorithm to characterize the electron track. As an alternative to the conventional approach of computationally simulating DNA damage by spatial overlay of an electron track on DNA, this algorithm instead focuses on quantifying the distance between ionizations in an electron track and next determining the likelihood that any given ionization pair forms a DSB. The first step of the algorithm involves electron characterization while the second step relies on DNA molecule characterization. By assuming a DSB biological endpoint and determining the DSB yield as a function of electron energy, energy dependent RBE values were estimated for monoenergetic electrons from 10 eV to 1 MeV. Photon RBE values, x-ray RBE values and radionuclide RBE values were also calculated and reported in this work in addition to electron RBE values. Photon RBE values were estimated based upon the electron RBE calculation. Photon RBE values were reported from 1 eV to 10 MeV. In turn, x-ray RBE values were calculated based upon photon values for several tube voltage and filter combinations. Finally, RBE values for over 1000 radionuclides were estimated and reported.