Three closely related forms of flightless leaf beetles belonging to the Chrysolina angusticollis species complex are parapatrically distributed in the vicinity of Sapporo, Japan. We studied sexual isolation between the three forms by no choice and multiple choice designs of crossing experiments. Sexual isolation was strong, the isolation index according to Malogolowkin-Cohen et al. (1965) being 0.350-0.951, but not enough to completely prevent gene flow between the forms. Furthermore, sperms kept by females of different forms were viable and active, although the quantity was smaller in some heterogamic combinations. The results suggest that a strong postzygotic isolation operates in the contact zones of these strictly parapatric forms.

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DNA was amplified from individual fossil pollen grains of Abies spp. (Pinaceae), which have been detected from Pleistocene peaty deposits (at least 150,000 years old). To identify the species of the fossil pollen by DNA analysis, the region indicating the species-specific sequence was searched among extant Abies species and the spacer region between rrn5 and trnR in chloroplast DNA was sequenced for four grains of the fossil pollen. Three pollen samples produced the same sequence as extant Abies species. The sequence for the remaining sample differed from that of extant Abies by one substitution. This study showed not only a successful DNA analysis from a single grain of fossil pollen but also a new method to identify the species of fossil pollen for the pollen analysis field.

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Changes in peroxidase activity in young inflorescences of Tradescantia clone BNL 4430 were investigated after treating with maleic hydrazide (MH) alone, X rays alone, or MH and X rays in combinations. MH is a promutagen known to be activated into a mutagen in plant cells. The treatments with MH were conducted for 4 h at a fixed concentration of 1 mM, and the X-ray doses applied were 768 to 882 mGy. For the combined treatments, X rays were delivered either 20 h before starting, or 2 or 20 h after completing the 4-h MH treatments. The treatments with MH alone and X rays alone both increased peroxidase activity, as compared with the controls. The combined treatments of delivering X rays 20 h before starting the MH treatments resulted in marked increases in the activity of this enzyme. However, the increases in peroxidase activity after the combined treatments of X-raying 2 h after completing the MH treatments were small, and the activity rather decreased by X-raying 20 h after completing the MH treatments. These results are consistent with our earlier findings that clear synergistic effects of MH and X rays in inducing somatic pink mutations in the stamen hairs of clone BNL 4430 were detected by treating with X rays before MH treatments, whereas antagonistic effects of MH and X rays were often observed by delivering X rays during or after MH treatments (Xiao and Ichikawa, 1995). It is therefore highly likely that peroxidase is certainly involved in the activation of MH into a mutagen, and that the increases and decreases in peroxidase activity after different combined treatments are related to the occurrences of synergism and antagonism, respectively, between MH and X rays.

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Variation of spontaneous somatic mutation frequency was studied in the stamen hairs of Tradescantia clone BNL 02 heterozygous for flower color (blue/pink; the blue color being dominant), one of the most stable clones in terms of spontaneous mutation frequency. Young inflorescence-bearing potted plants of this clone were grown under several different controlled environmental conditions, and the spontaneous pink mutation frequency in the stamen hairs was scored daily for three (partly two) weeks. The average number of hairs per stamen decreased as inflorescences became older, especially during the first one week or so after the inflorescences initiated flowering. The average number of cells per hair also decreased with the age of inflorescences, but the decreases were much smaller than those in the number of hairs. On the other hand, the spontaneous mutation frequency expressed as the number of pink mutant events per 10⁴ hair-cell divisions did not show any significant changes with the age of inflorescences. The spontaneous mutation frequency varied, however, depending on the controlled environmental conditions and showing nearly significant negative and positive correlations with average temperature and diurnal temperature difference, respectively, although the variation observed was very much smaller than those reported earlier in a temperature-sensitive mutable clone KU 20 and also smaller than those in other clones.

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We consider two loci (or DNA sites) in which mutation occurs from the wild-type allele A₁ (resp. B₁ to a mutant allele A₂ (resp. B ₂) in the first (resp. second) locus. Gene combinations or haplotypes with a single mutation, A₁B₂ or A₂B₁ are deleterious. The double mutant, however, does not have the harmful effect of the single mutations. This model is a two-locus two-allele model with compensatory fitness interaction. With this model and a finite population, the average time until fixation of the double mutant, A₂B ₂, starting from the state in which the population consists exclusively of A₁B₁ is calculated. We show that linkage between the loci is an important factor in the average time until fixation and that compensatory fitness interaction can be a mechanism for molecular evolution when linkage between the loci is not weak. Deleterious mutation can accelerate the speed of fixation of a double mutant. An interpretation of this phenomenon is presented.

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The chloroplast DNA (ctDNA) of barley (Hordeum vulgare L.) was isolated from young green leaves and fragments after partial digestion with Sau3A were cloned into a lambda phage vector. Using an overlapping clone bank of the entire chloroplast genome of barley, we mapped the cleavage sites for the enzymes XbaI, HindIII, PstI, SalI and PuvII precisely on the circular DNA. The chloroplast genome of barley was found to be 137 kbp long and to contain a pair of inverted repeat regions of 23.7 - 21.1 kbp that separated two single-copy regions of 81.7 - 81.1 kbp and 13.2 - 10.6 kbp, respectively. The restriction map of the barley chloroplast genome showed a high degree of conservation of restriction sites relative to those in the chloroplast genomes of wheat and rye. The genes for 13 transfer RNAs and 33 chloroplast proteins were identified and located on the barley chloroplast genome by hybridization with fragments of rice ctDNA that contained the corresponding genes. The locations of the various genes are very similar to the respective positions on the chloroplast genome of rice and maize.

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Chiasma frequency and chiasma distribution pattern of three parasite flukes, Schistosoma mansoni (n=8), S. japonicum (n=8), and Paragonimus ohirai (n=11) were investigated by using the chiasma distribution graph. It was revealed that there is a minimum value of interference distance between two interstitial chiasmata in each bivalent (1.8% of the total bivalent length), but frequency distributions of interstitial chiasmata are random and almost uniform except the centromere and telomere regions in which chiasma formation is suppressed. As no chiasma terminalization was detected, the so-called terminal chiasma were best interpreted by an achiasmatic terminal association resulting from the telomerenuclear membrane association. The mean chiasma frequency per cell estimated from interstitial chiasmata is 15.3 in S. mansoni and P. ohirai, but very low (3.0) in S. japonicum. A genetic mechanism controlling the level of chiasma frequency was discussed with reference to the results in mammals.

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Intergeneric hybrid plants were obtained by the sexual crossing of Diplotaxis muralis DC, a C₃ species, and Moricandia arvensis (L.) DC, a C₃-C₄ intermediate species. The morphological characteristics and chromosome numbers showed that these plants were true hybrids. The hybrid had a CO₂ compensation point of 27 μl/ L, nearly as low as that of M. arvensis (20 μl/L). A C₃-like value of 45 μl/L for this point was found in somatic hybrids produced in our laboratory by protoplast fusion between red cabbage (Brassica oleracea L. var. capitata) or cauliflower (Brassica oleracea L. var. botrytis) and M. arvensis. However, significant differences were not found among the sexual and the somatic hybrids in the concentration or total activity of ribulose-l,5-bisphosphate carboxylase/oxygenase. The results showed that the expression, of a C₃-C₄ intermediate character of photosynthesis from M. arvensis appears to depend on the combination of other characters of the parental species.

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