The relative sensitivity of the soaked seeds of nine gymnosperm species to gamma radiation

Abstract

Seeds of nine gymnosperm species, soaked in water to full imbibition, were irradiated with 137Cs gamma rays in two separate experiments. Species studied were Larix laricina, Picea abies, Picea glauca, Picea mariana, Pinus banksiana, Pinus contorta, Pinus resinosa, Pinus sylvestris and Thuja occidentalis. In the first experiment exposures of 150, 300, 600, 1200, 2400, 4800, 9600, 19,200 and 38,400 R were used and the seedlings were grown for 36 days after initial germination in perlite saturated with a complete nutrient solution. In the second experiment exposures of 150, 300, 450, 600, 900, 1200, 1800, 2400, 3600, 4800, 7200, 9600, 14,400 and 19,200 R were employed and the seedlings were grown in sand for 75 days after initial germination. Endpoints scored in the first experiment were germination, survival, cotyledon length, and plant dry weight. In the second experiment germination, survival, hypocotyl length, cotyledon length, shoot length, root length, shoot dry weight, and root dry weight were scored. Seed radiosensitivity varied by a factor of 3·80–7·33 in the first experiment and from 2·67 to 5·70 in the second experiment, depending on the endpoint used. Picea abies, Picea glauca and Pinus sylvestris were the most sensitive species in both experiments and Pinus banksiana the most resistant. The average D 50 (exposure resulting in 50 per cent inhibition) for all endpoints in Experiment I varied from 2·64 kR to 9·71 kR; that in Experiment II from 2·30 kR to 10·56 kR for the nine species studied. Comparison of the results with previous reports for individual species indicated that relative radiosensitivity of seed of plant species must be investigated with all species of interest being identical in radiation exposure conditions, seed moisture content and post-irradiation storage. Germination and growing conditions optimal for each species are suggested. The more than four-fold average differences in seed radiosensitivity were found to be unrelated to differences in nuclear volume, chromosome volume, and DNA content previously reported for the same populations of these species. The relative seed sensitivity pattern showed no relation to previously reported predictions of seedling and mature plant sensitivities for the same species.