The interaction between plant hormones throughout plant regeneration and development is complex. In the present study, we extended our investigation and disclosed the capacity of de novo shoot organogenesis from cotyledon explants of bottle gourd in relation to plant hormones and ethylene inhibitor. Synergistic effect of kinetin and benzyl adenine (BA) enhanced the shoot regeneration efficiency (80.6%) from cotyledon explants of bottle gourd, compared with BA or kinetin used separately, even in the presence of AgNO₃. The use of BA or kinetin separately or in synergistic combination led to a characteristic brownish color of the explants at the bud formation stage which was related to ethylene production. In the cotyledon explants cultured on MS medium supplemented with kinetin, the production of ethylene was lower than when BA or the combination of BA and kinetin was used. However, the regeneration capacity was very low and the emergence of shoot buds was delayed. BA promoted ethylene production while the synergistic effect of kinetin and BA decreased ethylene production and played a role in high frequency of regeneration from cotyledon explants of bottle gourd. The physiological relevance of the hormonal interaction in relation to the regulation of ethylene action and effect on regeneration was discussed.

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The nucleotide sequence of a gene, Hf1, encoding the flavonoid 3′,5′-hydroxylase in commercial petunias was compared to those in natural species to reconstruct historical events that occurred at the Hf1 locus in commercial petunias in the course of breeding since the 1830s. Intact Hf1 genes of any natural species so far studied were not detectable in 84 commercial petunias examined and were considered to have been removed by breeders. The dominant Hf1 alleles isolated from 14 Hf1 Hf1 cultivars showed an identical open reading frame (ORF) sequence and were considered to result from inter-allelic recombination between Hf1 of Petunia axillaris subsp. axillaris or subsp. parodii and Hf1 of P. integrifolia subsp. integrifolia or P. inflata, which were recorded as or assumed to be the historical parents of commercial petunias. Recessive hf1-3 was considered to be a mutant allele of the recombined Hf1 associated with the insertion of a retrotransposable element (rTph1) into exon III. The recessive hf1-2 allele showed a sequence identical to that of Hf1 of P. integrifolia subsp. integrifolia and P. inflata, except for a transposable element (dTph9) inserted into exon III and a target site duplication. We analyzed the potential causes of the recombination that occurred at the Hf1 locus and of the removal of dominant Hf1 genes of natural species from commercial petunias.

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To learn the genome constitution and the origin of Japanese current rice (Oryza sativa) cultivars, we studied the number of distinct genotypes and the organization of genome segments with these genotypes in these cultivars. We studied the genotype divergence in 25 Japanese elite and local cultivars by analyzing their DNA sequence divergence at 23 loci and restriction fragment length polymorphisms (RFLP) at 44 loci. These analyses showed that most of the polymorphic loci among the cultivars comprised only two sequence types or alleles, suggesting that their genomes are constituted mostly by a limited number of (possibly as few as two) genotypes. Each of the distinct genome segments appeared to have originated from distinct progenitors of the Japanese current cultivars. The graphical representation of genotypes generated based on the polymorphism data revealed that the genomes of Japanese rice cultivars were mosaics constituted mainly from the two types of progenitor chromosome segments, and that the organization of these genotypes was specific to each cultivar. In contrast to the Japanese cultivars, Chinese and Korean local japonica rice cultivars exhibited greater divergence both in the number of constitutive genotypes and in the pattern of their organization. Our results indicate that Japanese rice cultivars are composed of one subgroup of japonica cultivars that have undergone “population bottlenecks” through the course of their introduction to Japan and during subsequent selection and dissemination.

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Genes involved in the fertility restoration (Rf) of wild-abortive (WA)-type cytoplasmic male sterility (CMS) in rice have not been clearly identified, because of the inconsistency of their number and map position. Although the Rf-1 genes, which restore Chinsurah Boro (BT)-type CMS, have been recently isolated, their effects on WA-type CMS are still unclear. In the present study, near-isogenic lines (NILs) of japonica rice, differing at Rf loci, were developed using marker-assisted selection (MAS) to determine the effect of each Rf gene on WA- or BT-cytoplasm in a japonica background. The NILs were crossed with a japonica CMS line, then the pollen and seed fertility of the hybrid plants was analyzed. The Rf-1 locus consisting of two Rf genes from IR36 was sufficient to restore fertility in the hybrids with BT-type CMS but conferred very little fertility to those with WA-type CMS. Rf-3 on chromosome 1, a weak Rf gene, and Rf-6(t) on chromosome 10 were unable to confer seed fertility to plants with BT-type or WA-type CMS. Both Rf genes, however, could accelate the development of abortive pollen in the case of WA-type CMS and their effect was additive. Crossing of CMS rice with chromosome segment substitution lines carrying Rf loci from IR24 resulted in similar pollen development and seed fertility.

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To identify the chromosomal regions controlling the eating quality of cooked rice, we performed a quantitative trait locus (QTL) analysis using 93 backcross inbred lines (BILs) and 39 chromosome segment substitution lines (CSSLs) derived from crosses between a japonica rice cultivar Koshihikari (glossier appearance, tasty, sticky and soft eating quality of rice when cooked) and an indica cultivar Kasalath (less glossy appearance, less sticky and hard eating quality of rice when cooked). We evaluated the eating quality of rice including overall evaluation (OE), glossiness (GL), taste (TA), stickiness (ST) and hardness (HA) in each line based on the sensory test of cooked rice. Twenty-one QTLs for eating quality were mapped to eight regions on chromosomes 1, 2, 3 (two regions), 6, 7, 9 and 10. The Koshihikari alleles at 19 out of 21 QTLs increased the eating quality, while the Kasalath alleles at the other two QTLs increased the eating quality. We also mapped the QTLs for chemical properties, such as amylose content (AC) and protein content (PC), which affected the eating quality. Four QTLs in the terminal region of the short arm of chromosome 3 and five QTLs on chromosome 6 for eating quality were mapped to the same region as that of the QTLs for AC. Three QTLs on chromosome 1 for eating quality were also mapped to the same region as that of a QTL for PC. The chromosome positions of the other QTLs for eating quality did not coincide with those of the QTLs for AC and PC. Six out of 21 QTLs for eating quality, qTA3, qOE6, qGL6, qTA6, qST6 and qHA6, were commonly identified by analysis using both BILs and CSSLs. One QTL, qTA3, was not a locus of AC, PC or known eating genes. Thus the QTL was mapped in the interval between the SSR markers RM1332 and RM6676 in the middle region of the short arm of chromosome 3 by fine mapping of three sub-CSSLs. Five QTLs, qOE6, qGL6, qTA6, qST6 and qHA6, seemed to be associated with the Waxy (Wx) gene located on chromosome 6.

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In the southwestern part of Japan, weakness of the dough produced from soft wheat used for white salted noodles, resulting from low protein content and poor protein quality, is one of the shortcomings in noodle quality. We investigated the effect of the high-molecular-weight glutenin allele, Glu-D1d, on dough properties and noodle quality using near-isogenic lines (NILs) of three soft wheat cultivars. The NILs with the Glu-D1d allele showed significantly stronger dough, based on the sodium dodecyl sulfate sedimentation volume and the proportion of unextractable polymeric protein in total polymeric protein, than that of the corresponding recurrent parents with the Glu-D1f allele, suggesting that the Glu-D1d allele exerts a positive effect on dough strength, even when the protein content is low (around 8.0%). The positive effect of the Glu-D1d allele on dough strength was most pronounced in the cultivar harboring the Glu-A1c allele (null allele) with weaker dough. Significant differences were found between the NILs and the corresponding recurrent parents in the breaking force of cooked noodles based on instrumental assessment and in the noodle firmness based on sensory assessment, suggesting that the dough strength conferred by the Glu-D1d allele affected the firmness of cooked noodles.

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