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  • Author or Editor: Masayoshi Shigyo x
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Eight kinds of japanese bunching onion [Allium fistulosum L. (genomes FF)]-shallot [Allium cepa L. Aggregatum group (genomes AA)] monosomic addition line [MAL (FF+1A-FF+8A)] were used to study the effects of single alien chromosomes from A. cepa on the production of carbohydrates in the leaf tissues of A. fistulosum. Carbohydrate contents in green leaf blades of these MALs were measured during alternate months from May 2005 to Mar. 2006. The determination of soluble sugar content from leaf blades of each MAL and A. fistulosum revealed that nonreducing sugars (sucrose and fructan) accumulated in winter leaf blades. Reducing sugar (fructose) in the leaf blades of each MAL was lower than A. fistulosum in almost every time period. In the leaf blades of FF+4A, high fructan accumulation was observed from Nov. 2005 to Mar. 2006. A series of determinations on the pectin content showed that amounts of NaOH-soluble pectin and HCl-soluble pectin remained at low levels at all time periods. High pectin accumulations in FF+7A and FF+8A occurred in September and slightly decreased in November. A decrease in hexametaphosphoric acid-soluble pectin content was associated with the maturity of MALs from autumn to winter, whereas the water-soluble pectin content increased. The pectin methylesterase and polygalactronase genes of shallot were assigned to chromosome 7A and 4A, respectively. These results demonstrate that important genes related to pectin metabolism in shallot are located on chromosomes 4A, 7A, and 8A of shallot.

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Bulb onion (Allium cepa L.) has a very large genome composed of a high proportion of repetitive DNAs. Genetic analyses of repetitive sequences may reveal microsatellites in order to increase the number of genetic markers in onion. Thirty microsatellites were previously isolated from an onion genomic library (Fischer and Bachmann, 2000). A complete set of Japanese bunching onion (A. fistulosum) – shallot (A. cepa Aggregatum group) monosomic addition lines were used to assign these microsatellites to the chromosomes of A. cepa. Simplified PCR conditions for each microsatellite were determined and 28 of the 30 primer pairs amplified DNA fragments, of which 21 microsatellite markers were assigned to chromosomes of A. cepa. Subsequent mapping of these microsatellites will enable us to establish the chromosomal distribution of these markers.

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Eight Allium fistulosum L.–Allium cepa L. Aggregatum group (shallot) monosomic addition lines (2n = 17, FF+1A–FF+8A) have been useful in revealing the effects of single alien chromosomes from A. cepa on the production of l-ascorbic acid in the leaf tissue of A. fistulosum. In this study, the determination of ascorbic acid content revealed that the incorporation of alien chromosome 1A into a diploid background of A. fistulosum increased the internal ascorbic acid content of the leaf blade tissue. We produced a 1A disomic addition in the tetraploid of A. fistulosum (2n = 34) and demonstrated high-frequency transfer of the alien chromosome in crosses with A. fistulosum. Five plants of the 1A disomic additions were regenerated via apical meristem culture of the FF+1A on a Murashige and Skoog medium containing colchicine. These 1A disomic additions showed partial fertility for female and male gametes. Most of the progenies from selfing of the 1A disomic additions and reciprocal crossing with A. fistulosum possessed chromosome 1A. Interestingly, 64% (18 of 28) of the plants obtained from the reciprocal crosses were 1A monosomic additions in a triploid background of A. fistulosum. These monosomic additions were more vigorous and vitamin C-rich than euploid plants of A. fistulosum.

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To clarify the role of gibberellin (GA) in the growth of bunching onion (Allium fistulosum), identification of endogenous GAs and expression analysis of a putative gibberellin 3-oxidase (AfGA3ox1) were conducted. GA1, GA3, GA4, GA9, GA20, and GA34 were identified with levels of GA4 and GA9 being higher than those of GA1, GA3, and GA20. The young seedlings were clearly elongated by exogenous GA4 treatment but not by GA3. These results indicate that the 13-non-hydroxylation pathway of GA biosynthesis may be predominant in shoots with GA4 playing an important role in the growth of bunching onion. Expression of AfGA3ox1 was higher in leaf sheaths than leaf blades during vegetative growth. In reproductive organs, expression of AfGA3ox1 was higher at early and middle development stages in the stalks but was detected at a late development stage in the umbels. AfGA3ox1 was mapped on chromosome 7A from shallot, a bunching onion-related species.

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