Mutagenesis of enzyme loci induced in Pinus sylvestris L. megaspores by ionizing radiation following the Chernobyl nuclear accident

Polyacrylamide gel electrophoresis is used to study the mutagenesis of 20 enzyme loci in Pinus sylvestris populations induced in megaspores by ionizing radiation during the first month following the Chernobyl nuclear accident. The frequency of mutations altering enzyme synthesis in endosperms (megagametophytes) within the 30-km zone is found to average 2.7x10-3 per gene. The relationship between the dose rate of gamma irradiation and the mutation frequency is quantified: for low doses it increases linearly, while for high doses it drops due to the marked decrease in the number of viable seeds. The main types of genetic changes revealed by the method of electrophoresis are null variants, mutations altering the electrophoretic mobility of protein molecules in the gel, and duplications. Data are presented on the genetic efficiency of a 1 Gy dose, which is 1x10-3 mutations per gene. Different loci are found to differ in their radiosensitivity. The calculations show that the value of the dose doubling the spontaneous level of mutations in megaspores in the 30-km zone ranges from 0.5 Gy to 1.5 Gy depending on the dose rate