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Caixi Zhang, Kenji Tanabe, Fumio Tamura, Akihiro Itai and Shiping Wang

The aim of this study was to investigate the roles of spur characteristics and carbon partitioning in regulating cultivar differences in fruit size of two late-maturing japanese pear cultivars, `Atago' and `Shinkou'. The study of spur characteristics showed that the two cultivars displayed different patterns in leaf development, flower characteristics, fruit growth, and shoot type. In contrast to `Atago' with dramatically larger fruit, `Shinkou' is a heavily spurred cultivar with a higher total leaf area and leaf number per spur early in fruit growth, less vegetative shoots, and smaller fruit but larger core. No significant differences were obtained in specific leaf weight, leaf thickness, chlorophyll content, and net photosynthesis of mature leaves, and seed number per fruit between the two cultivars. The results of trace experiment with 13C revealed that on a spur basis, there were no significant differences in the amount of 13C assimilate produced by spur leaves on each labeling date except at 190 days after anthesis, however, there were highly significant differences in the amount of 13C allocated to fruit between cultivars. Moreover, a higher amount of 13C assimilates was allocated to `Atago' flesh (or fruit) than that in `Shinkou'. Analysis of relative sink strength (RSS) indicates that the sink strength of fruit was dominant over those of other organs in the spur measured in both cultivars except at the early stage of fruit growth. `Atago' exhibited a greater RSS of fruit and lower losses of 13C for respiration and export than `Shinkou'. These results suggest that the movement of photosynthates into the fruit was determined by sink strength of the fruit rather than the source strength in the two cultivars.

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Yuanwen Teng, Kenji Tanabe, Fumio Tamura and Akihiro Itai

A total of 118 Pyrus sp. (pear) and cultivars native mainly to east Asia were subjected to randomly amplified polymorphic DNA (RAPD) analysis to evaluate genetic variation and relationships among the accessions. Two hundred fifty RAPD markers were scored from 20 decamer primers. RAPD markers specific to species were identified. Clustering analysis revealed two divisions: one comprising cultivars of P. communis L., and the other including all accessions of Pyrus native to east Asia. The grouping of the species and cultivars by RAPD data largely agrees with morphological pear taxonomy. However, some noted incongruence existed between two classification methods. Pyrus calleryana Dcne. clustered together with P. koehnei Schneid., P. fauriei Schneid. and P. dimorphophylla Makino. Pyrus betulaefolia Bge. clustered with P. ×hopeiensis Yu and P. ×phaeocarpa Rehd. A noncultivated clone of P. aromatica Kikuchi et Nakai grouped with P. aromatica cultivars. Pyrus hondoensis Nakai et Kikuchi and cultivars of P. ussuriensis Max. formed a single group. Some accessions from Korea (named Korean pear) had species-specific RAPD markers and comprised an independent group. Most of the Chinese white pears clustered together with most of the Chinese sand pears. Based on the present results, the new nomenclature P. pyrifolia var. sinensis (Lindley) Teng et Tanabe for Chinese white pear was suggested. Most accessions of Japanese pears fell into one main group, whereas pear cultivars from Kochi Prefecture of Japan subclustered with some Chinese sand pears and one accession from Korea. Our results infer that some local Japanese pear cultivar populations may have been derived from cultivars native to Kochi Prefecture in Shikoku region, and that the latter may have been introduced from ancient China and/or Korea.

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Fumio Tamura, Kenji Tanabe, Akihiro Itai and Hiroshi Tanaka

The dormancy of Japanese pear (Pyrus pyrifolia Nakai) floral buds was broken by prolonged chilling or short-term high-temperature treatment (45 °C for 4 hours). Changes in the protein profiles of the floral buds were studied using two-dimensional electrophoretic analysis (2-DE). The quantities of nine cold-induced proteins (CIPs) increased in the floral buds with increases in chill unit (CU) value, but did not change rapidly when bud dormancy was near completion. When dormancy of floral buds was broken by high-temperature treatment, nine heat-shock proteins (HSPs) accumulated. These HSPs were distinct from the CIPs. The isoelectric point of the 19-kDa CIP shifted to the basic side by high-temperature treatment as well as by chilling. These results suggest that the 19-kDa protein may be a usable marker to measure the degree of bud dormancy in Japanese pear.

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Nobutaka Shiraiwa, Kaori Kikuchi, Ichiro Honda, Masayoshi Shigyo, Hiroko Yamazaki, Daisuke Tanaka, Kenji Tanabe and Akihiro Itai

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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Caixi Zhang, Kenji Tanabe, Hiroko Tani, Hiromitsu Nakajima, Minori Mori and Emi Sakuno

Both ‘Atago’ and ‘Shinkou’ are late-season japanese pear (Pyrus pyrifolia Nakai) cultivars with russet-brown fruit, and the progenies of crosses made between ‘Nijisseiki’ and unknown cultivars, but they display different growth habit, fruit size, and fruit quality. To clarify the difference in fruit development between the two cultivars, the levels of endogenous gibberellins (GA1, GA3, and GA4) and abscisic acid (ABA) in fruit were identified and quantified by gas chromatography/mass spectrometry, and a histological study of fruit was carried out. The results showed that cell number rather than cell size of mesocarp is responsible for the difference in fruit size between the two cultivars. Furthermore, analysis of endogenous bioactive gibberellins revealed that ‘Atago’ fruit has much higher levels of GA1, GA3, and GA4 than ‘Shinkou’ fruit during fruit development, particularly during the early period of fruit growth. However, ‘Shinkou’ has a much higher ABA level than ‘Atago’ during the early period of fruit development. Abscisic acid concentration remained at an extremely low level after the first production peak after anthesis in ‘Atago’ compared with ‘Shinkou’.