The effects of X-ray dose fractionations in inducing somatic mutations were studied in the stamen hairs of Tradescantia clone KU 9 heterozygous for flower color (blue/pink). Young inflorescence-bearing shoots with roots were prepared, and were exposed to X rays acutely. A dose-response regression line with a slope of 1.454 on a log-log graph was obtained for single acute X-ray doses of 0.255 to 1.03 Gy, and it showed that somatic mutation frequency increased curvilinearly with increasing X-ray dose. When 1.00 to 1.15 Gy of X rays were fractionated into two acute doses of about halves given with intervals of 5 to 120 min, decreases in induced mutation frequency were observed. The mutation frequencies induced by the fractionated doses with intervals of 5 and 10 min were not significantly different from those expected for the total single doses. However, the mutation frequency decreased significantly at 5% level with 20- and 30-min intervals, and decreases were highly significant at 0.1% level when the interval was prolonged to 40 to 120 min. The results obtained indicate that the interaction between the first and second doses began to reduce between 10 and 20 min later, and disappeared by 60 min later. That is, the DNA and/or chromosomal breaks induced by the first dose began to be rejoined (repaired) or healed between 10 and 20 min later, and all of them were rejoined or healed by 60 min later, losing their abilities to interact with the DNA and/or chromosomal breaks induced by the second dose.
Forty one plants of alien monosomic addition lines of Allium fistulosum L. with extra chromosomes from A. cepa L. Aggregatum group (FF + nA) were produced through the second backcross of amphidiploids between these two species to A. fistulosum. Identification of the extra chromosomes in the 16 plants by elaborate karyotype analyses indicate that a complete series (eight different types) of the alien monosomic addition lines was established in Allium for the first time in this study. Chromosomal locations of malate dehydrogenase (MDH) gene, triosephosphate isomerase (TPI) gene and 5S rDNA of A. cepa Aggregatum group were determined using the series; The gene locus Mdh-1 was located on 4A, Tpi-1 on 3A and a 5S rDNA locus on 7A. Our previous and present studies using the alien monosomic addition lines revealed 11 genetic markers (isozyme and 5S rDNA) assigned to all eight chromosomes of A. cepa Aggregatum group, and these markers reconfirmed the completion of the series. Extra chromosomes of 25 other plants were examined by means of simple analyses of the chromosome markers and karyotypes. Of the total 41 plants, frequencies of the alien monosomic addition lines with extra chromosomes 1A to 8A were as follows: 1A, 5 plants; 2A, 3; 3A, 5; 4A, 9; 5A, 4; 6A, 2; 7A, 11; and 8A, 2.
Three kinds of DNA sequences (here called TrsB, TrsC and RIRE1) have been previously reported to be those repeated in tandem specifically in the wild rice species with FF, CC or EE genome, respectively. To characterize these genome type-specific sequences, we carried out PCR using a pair of primers, which hybridize to a restricted region in the repeating unit sequence and prime DNA synthesis in both directions. Gel electrophoresis and DNA sequencing revealed that PCR using primers for TrsB (or TrsC) amplified the fragments with an integral series of a unit length not only from total DNA of the rice strain with FF (or CC) genome, but also from those of the rice strains with non-FF (or non-CC) genome. TrsB or TrsC was, however, found to be repeated in an extraordinary number of copies in the species with FF or CC genome, respectively, in which the TrsB (or TrsC) sequence has been originally identified. PCR using primers for RIRE1 produced various sizes of fragments from total DNA of the rice strains with EE genome. The fragments, however, showed no progression at interval of the unit length characteristic for tandem repeats. Nucleotide sequencing of the amplified fragments revealed that they were not the sequences repeated in tandem, but were those interspersed as an element having partial homology with the LTR sequences of retrotransposons, Wis-2-1A in wheat and BARE-1 in barley. RIRE1 was present in the rice species with any types of genomes, but in the species with EE genome in an extraordinary number of copies.
Four newly discovered and seven previously known Fagopyrum species were classified based on their morphology, isozyme variability, and RFLP of chloroplast DNA (cpDNA). Three independently constructed phylogenetic trees showed good agreement and we had sufficient confidence in them to assert that they probably reflect the phylogenetic relationships among the Fagopyrum species. The new classification differs from Steward (1930)'s classification in the position of Fagopyrum tataricum and F. gracilipes; F. tataricum is very close to F. cymosum. The new classification resolved several problems which we suffered from, when we used Steward's classifiction. Three new species, F. pleioramosum, F. callianthum and F. capillatum are closely related to F. gracilipes. New species F. homotropicum is very close to F. esculentum in morphology as well as in isozyme variability.