YEARLY VARIATION OF SPONTANEOUS SOMATIC MUTATION FREQUENCY IN THE STAMEN HAIRS OF TRADESCANTIA CLONE KU-9 GROWN OUTDOORS, WHICH SHOWED A SIGNIFICANT INCREASE AFTER THE CHERNOBYL ACCIDENT

Scoring of spontaneous somatic pink mutation frequency in the stamen h airs of Tradescantia clone KU 9, a heterozygote for flower color (blue /pink; the blue color being dominant), was carried out for 11 years on plants grown outdoors, during the period of May 11-31 (for 3 weeks) i n every year from 1982 to 1992. Weekly and yearly variations of the sp ontaneous mutation frequency were observed, and such variations could mostly be correlated to the difference in temperature. That is, the mu tation frequency was generally higher in the weeks and years when the temperature was relatively low, showing the strongest negative correla tion with the average minimum temperature. The variations were also co rrelated to the diurnal temperature difference, the mutation frequency being higher with larger diurnal temperature difference in general. H owever, the mutation frequency observed in 1986 was exceptionally high er than that expected from the temperature for this year, and was very significantly higher than for other years. The scoring of mutation fr equency was thus continued in 1986 for an additional 4 weeks (June 1-2 8), and it was confirmed that such higher mutation frequencies lasted for 6 weeks in total. The exceptionally high mutation frequency seemed to be related to the radioactive fallout which occurred in early to m id May of 1986, even in Japan, after the serious nuclear reactor accid ent at Chernobyl, and also to the biological concentrations of radioac tive nuclides which subsequently occurred, although it was difficult t o conclude this definitely. The mutation frequency in 1987 was second highest, and was also significantly higher than the lowest mutation fr equency observed in 1990.