Genkichi Takeda

The diversity of interspecific pollen-pistil incongruity in Nicotiana

Nicotiana tabacum was used as a pistillate parent and crossed with three self-compatible species, N. rustica, N. repanda and N. trigonophylla, which were previously reported to have pollen tubes unilaterally inhibited by N. tabacum pistil. Temporal and morphological observations revealed distinct differences of pollen tube behavior among these incongruous crosses. Pollen tubes of N. repanda were arrested in stigma and those of N. rustica in the middle of the style. On the other hand, pollen tubes of N. trigonophylla continued growing at a slow rate. Tubes of N. repanda and N. rustica showed morphological abnormalities such as swelling, thick wall, and irregular callose deposition. In addition, tubes of N. rustica often elongated in reverse direction and wound about in the middle of the style. Although the tubes of N. trigonophylla were apparently normal in morphology, they were distributed throughout the transmitting tissue, differing from the self-pollination of N. tabacum in which they were confined to the peripheral region of it. The diversity of pollen tube behavior indicates that physiological causes of incongruity are different among the three crosses. Bud pollination enabled pollen tubes to reach the ovary in all crosses, indicating that the N. tabacum pistil acquired its ability to inhibit foreign pollen tube elongation with its development. When interspecific hybrids between N. tabacum and the other three species were pollinated by parental species, tubes reached the ovary in all crosses, but the elongation rate of tubes slowed down and morphology was abnormal.

Hybrid plant of Phaseolus vulgaris L. and P. lunatus L. obtained by means of embryo rescue and confirmed by restriction endonuclease analysis of rDNA

SummaryHybridizations between three lines of the common bean (Phaseolus vulgaris L.) and two lines of the lima bean (P. lunatus L.) were attempted in order to transfer characters from the lima bean to the common bean. A total of 115 interspecific hybrid embryos were rescued and cultured, and 7 plantlets were eventually transferred to soil. The most compatible cross was ‘Edogawa XPI164891’, which had a high proportion of expanded ovules, and from which we obtained one mature interspecific hybrid. In general, morphological characters of the hybrid were intermediate between the parents, and the chromosome number of the hybrid was 2n=22 the same as that of both parents. The hybrid nature of the progeny plant was confirmed by restriction endonuclease analysis of rDNA. Species specific fragments were detected when total DNA was digested by BamHI, and BamHI-digested total DNA of the hybrid contained all fragments from both parents. Selves and backcrosses were attempted, but no progeny were obtained. The only hybrid obtained was completely sterile and meiosis highly irregular.

The use of IAA to overcome interspecific hybrid inviability in reciprocal crosses between Nicotiana tabacum L. and N. repanda Willd.

SummaryFlowering hybrid plants were obtained from reciprocal crosses between N. tabacum L. (2n=48) and N. repanda Willd. (2n = 48), in which cross incompatibility and hybrid inviability were manifested. Stylar pollination and ovule culture were used to overcome the cross incompatibility of stylar barriers and ovular death. It was shown that application of 2 mg/l indole-3-acetic acid (IAA) during the growth period, from the fiveto six-leaf stage to the flowering stage, is a useful and easy method to overcome hybrid inviability.

Rapid conversion of rDNA intergenic spacer of diploid mutants of rice derived from γ-ray irradiated tetraploids

The organization of tandemly repeated sequences of ribosomal DNA (rDNA) in rice mutants derived from γ-irradiated tetraploids was analyzed. Southern hybridization analysis of nuclear DNA revealed that most of the intergenic spacers (IGSs) in mutant rDNA are replaced concertedly by new molecular species. The new IGSs are produced by the amplification of a subrepeat of about 250 bp. Results obtained from sequence analyses indicate that various intermediate molecular species of the subrepeat were formed during structuring of the IGS region and that many rearrangements occurred between them. These findings demonstrate the effectiveness of recurrent irradiation of tetraploids for inducing artificial genome rearrangement, and also indicate the extreme plasticity and variability of genome structure in plants.

Two single-base substitutions involved in altering in a paired-box of AAATAC in the promoter region of soybean lipoxygenase L-3 gene impair the promoter function in tobacco cells

Abstract We have characterized the lox3 gene, a mutant form of Lox3 that encodes soybean seed lipoxygenase L-3. L-3 null mutants exhibit no detectable accumulation of the Lox3 transcript. Nucleotide sequencing of the 5′-flanking regions (−861 to +1 of the translation initiation site) of Lox3 and lox3 revealed that three substitutions (mut1, mut2 and mut3) are unique in the mutants. Interestingly, mut1 and mut2 are involved in changing a paired-box of AAATAC. The promoter region of either Lox3 or lox3 was fused to the coding region of the β-glucuronidase (GUS) gene and these fusion genes were expressed transiently in tobacco suspension-cultured cells. Gross reduction of GUS activity in the tobacco cells carrying the GUS gene driven by the lox3 promoter was observed. Repair of either mut1 or mut2 to wild type in the fusion gene by site-directed mutagenesis resulted in the recovery of GUS activity to the wild-type level, while repair of mut3 to wild type had less effect on the GUS gene expression. These results indicate that mut1 and mut2 occur in redundant cis-acting elements, probably in the paired-box, suggesting the molecular basis for the L-3 null mutation.

Studies on the procedure of mutation breeding with, six-rowed barley. : I. The methods of procedure in X1 and X2 generations.

The methods of mutation breeding were applied on six rowved barly in three ways. The dormant seeds were treated with 15 Kr of X-rays. Method A : After 3 ears were havested from each X1 Plant and one grain was removed from each ear, these grains were planted in bulk at X2 Mlethod B : After one ear was harvested from each Xl plant, the grains were planted separately as ear progenies at X2Method C : After 3 ears were harvested from each Xi Plant, the grains were planted separately as plant progenies at X2 Method A was compared with B and C. The eharacters mainly analyzed were earliness and stems;shortness. The selection of such aberrants was carried out in X2 (Table 1), and these were confirmed as mutants in X3 (Tables 2 and 3) . In the case of method A-ll (Table 1), selection was made by measuring stem length at X2 generation. In the case of other methods, selection was made by observation. 1) By using method A, the mutant types found n X2 Were more frequently observed compared with the other two methods and the mutant much deviated from the parent type were involved.This result was compatible with the theoretical consideration of YOSHIDA (1962). 2) Much better selection of short stem mutants was made in X2 by method A (I+II) than by methods B and C. This result demonstrates that the individual selection using this measurement was made much better than the pedigree selectian through observation.