Relative Cytogenetic Efficiency of Muons and π - Mesons in Zea mays (L.) and Its Modification by Postirradiation Storage

Abstract

Until recently, high-energy meson beams of sufficient intensity have not been available for biological research. The Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory now produces rmeson and muon (uparticle) beams suitable for use in biological experiments. The beam intensity is still low compared to that of other radiation sources. To achieve any measurable effect with most biological materials, long exposures are required. Dormant dry seeds, which have a low metabolic rate, seem especially well adapted for investigations at the present time. Special genetic stocks of Zea mays (L.), heterozygous for Yg2/yg2 alleles, have been used previously to study mutagenic effects of X-rays (1-3), deuterons (4), heavy cosmic particles (5), monoenergetic fast neutrons (6) and chemicals (2, 3). Seeds of these stocks were used in the experiments reported here. Presence of the dominant Yg2 allele produces a green color in the leaf, the recessive yg2 gives a yellowgreen color, and the heterozygote Yg2/yg2 has normal green leaves. Loss of the locus (deletion) or of function (mutation) for the dominant Yg2 allele gives a yellowishgreen phenotype in leaf cells and cell lineages of the altered genotypes. The frequency of yellow-green streaks or sectors in leaves was used as a measure of the frequency of radiation-induced genetic change or damage which was considered to be due mainly, if not exclusively, to breaks in the chromosome between the centromere and the Yg2 locus, with loss of the Yg2-containing segment. In the present