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Ryutaro Tao and Akira Sugiura

Callus cultures were initiated in the dark from leaf primordia, stem internodes, and young leaves of adult Japanese persimmon (Diospyros kaki L.) to induce adventitious buds. A high frequency of regeneration occurred on Murashige and Skoog medium (MS) with half the normal NH4NO3 and KNO3 concentration (1/2N) and containing 10 μm zeatin or 1 μm 4PU-30 in combination with 0.1 μm IAA, or MS(1/2N) medium containing 0.03 to 0.1 μ m IAA or 0.01 to 0.03 μm NAA combined with 10 μm zeatin. No significant differences in the capacity of regeneration were observed among the calli from different explant sources. Only eight of 16 cultivars formed adventitious buds on MS(1/2N) medium containing 10 μm zeatin and 0.1 μm IAA, with the percentage of explants forming adventitious buds ranging from 2% to 72%. Chemical names used: indole3-acetic acid (IAA); 1-naphthaleneacetic acid (NAA); N-phenyl-N'-(2-chloro-4-pyridyl)urea (4PU-30).

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Takuya Tetsumura, Hisajiro Yukinaga and Ryutaro Tao

Growth of micropropagated Japanese persimmon trees (Diospyros kaki L. cv. Nishimurawase) during the initial 3 years after field establishment was compared with that of grafted trees on seedling stocks. Judging from the mean length of annual shoots per tree and the yearly increases in height, trunk diameter, and top and root dry mass, the grafted trees on seedling stocks grew poorly during the first and second growing seasons, while micropropagated trees, raised in an outdoor nursery, developed poorly only during the first growing season. In contrast, micropropagated trees raised in pots fared well soon after field establishment. These trees had more fine than middle and large roots; in contrast, grafted trees on seedling stocks had one large taproot, which died back to some extent after field establishment, with few fine roots.

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Takuya Tetsumura, Ryutaro Tao and Akira Sugiura

A potentially dwarfing rootstock for japanese persimmon (Diospyros kaki L.) was propagated by single-node stem cuttings taken from root suckers. When a mature tree was cut down at ground level and part of the roots was exposed to the air, numerous suckers formed on the exposed parts of the roots. Single-node stem cuttings 3 to 4 cm (1.2 to 1.6 inches) long survived and rooted better than 10-cm (3.9-inch) and 25-cm (9.8-inch) leafy stem cuttings with several buds. Dipping cuttings in 3000 mg·L-1 (ppm) IBA for 5 s or in 25 mg·L-1 IBA for 24 h resulted in similar rooting. Most of the single-node stem cuttings taken in late-June and July survived and rooted well, whereas those prepared in late August rooted poorly and few survived. The survival and rooting percentages were unaffected by the position on the suckers (top vs. base) from which cuttings were taken. High relativehumidity in the propagation frame appeared to enhance survival and rooting. This clonal propagation method will make a rapid multiplication of japanese persimmon, a difficult-to-root species, possible. Chemical name used: indole-3-butyric acid (IBA).

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Mihoko Tamura, Ryutaro Tao and Akira Sugiura

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Tomoya Esumi, Ryutaro Tao and Keizo Yonemori

Japanese pear (Pyrus pyrifolia) and quince (Cydonia oblonga), both classified in the subfamily Maloideae, show differences in inflorescence architectures despite of the fact that they are genetically closely related. We previously isolated flowering related genes, LEAFY (LFY) and TERMINAL FLOWER 1 (TFL1) homologues, from these species and showed that they had two types of homologues for each gene. In this study, we examined the expression pattern of LFY and TFL1 homologues in these species by in situ hybridization and RT-PCR. The floral bud was dissected to small pieces under stereomicroscope; apical meristem, scales/bracts, pith, floral meristem, and inflorescence; and then used for RT-PCR. The LFY homologues were expressed in apical meristem and scales/bracts before the floral differentiation in both Japanese pear and quince. After floral differentiation, the expression was observed in floral meristem, scales/bracts and pith in both the species. The TFL1 homologues were strongly expressed in the apical meristem, but their expression was drastically decreased just before floral differentiation. It is considered that the decrease of expression of TFL1 homologues is a sign of floral initiation. The expression of TFL1 homologues was transiently increased at the beginning of floral differentiation in both species. Moreover, one of TFL1 homologues in Japanese pear was continuously expressed in the inflorescence part in the floral primordia, whereas expression of TFL1 homologues in quince almost completely disappeared after a solitary floral meristem was initiated. It was suggested that TFL1 homologues may also be involved in the inflorescence development of Japanese pear.

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Mihoko Tamura, Ryutaro Tao and Akira Sugiura

Interspecific hybrids between Diospyros glandulosa (2n = 2x = 30) and D. kaki cv. Jiro (2n = 6x = 90) were produced by electrofusion of protoplasts. Protoplasts were isolated from calli derived from leaf primordia, fused electrically, and cultured by agarose-bead culture using modified KM8p medium. Relative nuclear DNA contents of calli derived from fusion-treated protoplasts were determined by flow cytometry. One-hundred-forty-nine of 166 calli obtained had the nuclear DNA content of the sum of those of D. glandulosa and D. kaki cv. Jiro. RAPD analysis showed that the 149 callus lines yielded specific bands for both D. glandulosa and D. kaki cv. Jiro and they appeared to be interspecific somatic hybrid calli. Shoots were regenerated from 63 of the 149 interspecific hybrid calli. PCR-RFLP of chloroplast DNA analysis, flow cytometric determination of nuclear DNA content, and RAPD analysis revealed that the 63 interspecific hybrid shoot lines contained nuclear genome from both the parents but only chloroplast genome from D. glandulosa. Microscopic observation of root tip cells confirmed that somatic chromosome numbers of the interspecific hybrids were 2n = 8x = 120.

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Ryutaro Tao, Tsuyoshi Habu, Hisayo Yamane, Akira Sugiura and Kazuya Iwamoto

Self-compatible cultivars of Japanese apricot (Prunus mume Sieb. et Zucc.) have a horticultural advantage over self-incompatible ones because no pollinizer is required. Self-incompatibility is gametophytic, as in other Prunus species. We searched for molecular markers to identify self-compatible cultivars based on the information about S-ribonucleases (S-RNases) of other Prunus species. Total DNA isolated from five self-incompatible and six self-compatible cultivars were PCR-amplified by oligonucleotide primers designed from conserved regions of Prunus S-RNases. Self-compatible cultivars exhibited a common band of ≈1.5 kbp. Self-compatible cultivars also showed a common band of ≈12.1 kbp when genomic DNA digested with HindIII was probed with the cDNA encoding S 2-RNase of sweet cherry (Prunus avium L.). These results suggest that self-compatible cultivars of Japanese apricot have a common S-RNase allele that can be used as a molecular marker for self-compatibility.

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Nathanael R. Hauck, Amy F. Iezzoni, Hisayo Yamane and Ryutaro Tao

Correct assignment of self-incompatibility alleles (S-alleles) in sweet cherry (Prunus avium L.) is important to assure fruit set in field plantings and breeding crosses. Until recently, only six S-alleles had been assigned. With the determination that the stylar product of the S-locus is a ribonuclease (RNase) and subsequent cloning of the S-RNases, it has been possible to use isoenzyme and DNA analysis to genotype S-alleles. As a result, numerous additional S-alleles have been identified; however, since different groups used different strategies for genotype analysis and different cultivars, the nomenclature contained inconsistencies and redundancies. In this study restriction fragment-length polymorphism (RFLP) profiles are presented using HindIII, EcoRI, DraI, or XbaI restriction digests of the S-alleles present in 22 sweet cherry cultivars which were chosen based upon their unique S-allele designations and/or their importance to the United States sweet cherry breeding community. Twelve previously published alleles (S1, S2, S3, S4, S5, S6, S7, S9, S10, S11, S12, and S13) could be differentiated by their RFLP profiles for each of the four restriction enzymes. Two new putative S-alleles, both found in `NY1625', are reported, bringing the total to 14 differentiable alleles. We propose the adoption of a standard nomenclature in which the sweet cherry cultivars `Hedelfingen' and `Burlat' are S3S5 and S3S9, respectively. Fragment sizes for each S-allele/restriction enzyme combination are presented for reference in future S-allele discovery projects.

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Hisayo Yamane, Yukinobu Kashiwa, Tomomi Ooka, Ryutaro Tao and Keizo Yonemori

To understand the molecular basis of the endodormancy of buds of perennial plants, we searched for the genes that are expressed preferentially in endodormant lateral buds of the deciduous fruit tree japanese apricot (Prunus mume Sieb. et Zucc.) using suppression subtractive hybridization with mirror orientation selection (SSH/MOS). We generated two SSH/MOS libraries containing gene pools that are expressed preferentially in endodormant buds in comparison with paradormant or ecodormant buds to search for the genes that are upregulated by endodormancy induction or down-regulated by endodormancy release, respectively. Differential screening and sequencing indicated that genes involved in gibberellin metabolism, stress resistance, cell wall modification, and signal transduction, such as transcription factors, are upregulated in endodormant buds. After a further expression survey and full-length cDNA cloning, we found that a gene similar to the SVP/AGL24-type MADS-box transcription factor showed endodormancy-associated expression. Seasonal expression analysis suggested that the SVP/AGL24 homolog in japanese apricot might be involved in endodormancy regulation of its lateral buds.

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Young A Choi, Ryutaro Tao, Keizo Yonemori and Akira Sugiura

5S ribosomal DNA (rDNA) was visualized on the somatic metaphase chromosome of persimmon (Diospyros kaki) and ten wild Diospyros species by fluorescent in situ hybridization (FISH). The digoxigenin (DIG)-labeled 5S rDNA probe was hybridized onto the chromosomes and visualized by incubation with anti-DIG-fluorescein isothiocyanate (FITC). Strong signals of 5S rDNA probe were observed on several chromosomes of Diospyros species tested. Furthermore, multicolor FISH using 5S and 45S rDNA probes differently labeled with DIG and biotin, revealed separate localization of the two rDNA genes on different chromosomes of Diospyros species tested, suggesting that 5S and 45S rDNA sites can be used as chromosome markers in Diospyros. The number of 5S rDNA sites varied with the Diospyros species. More 5S rDNA sites were observed in four diploid species native to Southern Africa than in three Asian diploid species. The former had four or six 5S rDNA sites while the latter had two. Three Asian polyploidy species had four to eight 5S rDNA sites. Among the Asian species, the number of 5S rDNA sites seemed to increase according to ploidy level of species. These features of 5S rDNA sites were very similar to those of 45S rDNA sites in Diospyros. Phylogenetic relationship between D. kaki and wild species tested are discussed based on the number and chromosomal distribution of 5S and 45S rDNA.