In this paper, I review recent advances in research on Japanese pear rootstocks. Several clones of Pyrus betulaefolia and P. calleryana seedlings have been identified based on their ability to induce dwarfing scion growth, and their use in the future as dwarfing rootstock is anticipated. Among the various rootstock species, P. betulaefolia exhibits good adaptability to different environmental conditions, with high tolerance to drought, cold, and salt. This is due, in part, to P. betulaefolia’s superior ability to regulate osmotic potential and ability to maintain a high degree of unsaturation in fatty acids in biological membranes during cold hardening. P. calleryana exhibits not only a relatively high drought tolerance but also the highest flood tolerance. This tolerance depends on the ability of P. calleryana to shift to alcohol fermentation under anaerobic conditions and to expel the ethanol thus generated. These two rootstock species are highly effective in preventing fruit-hardening disorders. While P. betulaefolia exhibits high salt tolerance among native Asian Pyrus species, it is exceeded in this respect by two native Mediterranean species, P. amygdaliformis and P. elaeagrifolia, with a mechanism to inhibit the transport of salts from the roots to above-ground plant parts. Furthermore, P. xerophila exhibits superior Fe³⁺-chelate reductase activity in roots, endowing the species with tolerance to alkaline soils.

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The relationships between surface blushing and the content of qualitative components of the Japanese apricot ‘Nanko’ fruit were investigated. Brightly blushed fruit covering over 25% of its surface had higher levels of citric acid, phenolics, and antioxidant activity in its flesh than non-blushed fruit. Shading apricot fruit from ultraviolet (UV) light for about 3 weeks before harvest produced a clear decrease in surface blushing, phenolic content, and antioxidant activity. UV-B irradiation for 12 h to the inner canopy fruit 10 days before harvest resulted in blushing and increased the antioxidant activity. These results showed that brightly blushed fruit was rich in phenolics and antioxidant activity and that UV light played an important role in blushing, phenolic content, and antioxidant activity in the Japanese apricot ‘Nanko’ fruit. When fruit shaded from sunlight was exposed to sunlight for about 3 weeks before harvest by cutting off the shoot with leaves around the fruit to increase UV irradiation, surface blushing was caused, and the phenolic content and antioxidant activity in flesh were increased. On the other hand, placing reflecting films under the outer canopy for 40 days had no effect on the development of the bright red color.

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Hyuganatsu is a self-incompatible Citrus species with no parthenocarpic traits. Pollinizer requirements and seedy fruit production are therefore a limiting factor for Hyuganatsu growers. ‘Nishiuchi Konatsu’, a bud mutation of Hyuganatsu, can set fruit by self-pollination and aborts most seeds. To obtain a better understanding of the reproductive mechanisms of ‘Nishiuchi Konatsu’, its pollen was characterized by pollen observation and viability testing in vitro in addition to pollen tube observation of the pistil following various pollination combinations. Furthermore, the ploidy level of ‘Nishiuchi Konatsu’ and the progenies obtained after controlled pollination were analyzed using a flow cytometer. As a result, ‘Nishiuchi Konatsu’ pollen was shown to be functional in vitro, as indicated by both the pollen germination test and FDA staining. A curious feature of ‘Nishiuchi Konatsu’ pollen is that a giant pollen of about 42–44 μm in diameter, which is about 1.3-fold the average diameter of original Hyuganatsu pollen (33.4 μm), was partially produced. Observation of in vivo pollen germination and pollen tube elongation revealed that Hyuganatsu (or ‘Nishiuchi Konatsu’) × ‘Nishiuchi Konatsu’ showed imperfect incompatibility; that is, some pollen tubes were able to enter the style while others could not. Flow cytometry analysis indicated that ‘Nishiuchi Konatsu’ is diploid while all of its self-pollinated progenies, which were rarely obtained as normal seeds, were tetraploid. Progenies from other combinations were diploid. These results strongly suggest that unreduced 2n pollen production occurred in ‘Nishiuchi Konatsu’. In addition to self-compatibilty and seed abortion of ‘Nishiuchi Konatsu’ self-pollination, it has been reported that the proportion of normal to aborted seeds differs according to the cultivar of the seed parent crossed with ‘Nishiuchi Konatsu’ pollen (Honsho et al., 2009). Taking into account the unreduced pollen production as well as the effect of polyploidization on self-incompatibility and embryo development, we finally discussed why such a phenomenon was induced by pollination with ‘Nishiuchi Konatsu’ pollen and why ‘Nishiuchi Konatsu’ became self-compatible.

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Although Japanese mango is produced under a fairly unique cultivation system and fetches high prices at market, further growth of the mango industry in Japan requires the development of new cultivars. However, since individual mango flowers are quite small, no more than 1 cm in diameter, a large number of skilled workers is necessary for artificial pollination, thus making it difficult to obtain a sufficient number of progenies for breeding. We therefore evaluated a methodology whereby progenies were obtained by open pollination and their male parent was subsequently determined by DNA markers. Two mango cultivars (‘Irwin’ and ‘Beni-Keitt’) were arranged in a plastic house and honeybees were released as a pollen vector for open pollination. Harvested fruits were characterized and their seeds were sown in a bed. The male parent of the germinated seedlings was then identified by five simple sequence repeat (SSR) markers. As a result of SSR genotyping, the male parents of 185 of 239 ‘Irwin’ seedlings were revealed; 79 were obtained by self-pollination and 106 from out-crossing. For ‘Beni-Keitt’, the male parent of 14 of the 20 seedlings was determined with two self-pollinated and 12 out-crossed. Preferential out-crossing in ‘Irwin’ was revealed using the chi-square test, although the considerable number of self-pollinated fruit obtained shows that a sufficient number of fruit can be set in a single-planted orchard. The effect of the male parent on fruit characteristics was subsequently examined, revealing that in ‘Irwin’ the Brix value of self-pollinated fruits was significantly higher than that of cross-pollinated fruits. Certain color values were, however, lower in self-pollinated ‘Irwin’ fruits.

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Fluorescent banding patterns of pear chromosomes were determined from samples taken from root tips of open-pollinated seedlings of Pyrus pyrifolia (Burm. F) Nakai (Japanese pear), P. calleryana Decne. (Callery pear), P. pyrifolia × P. ussuriensis var. aromatica (a hybrid of Japanese pear and Iwateyamanashi), and P. mikawana Koidz. (Toyotomi Nashi). All accessions used in this study had 2n = 34 chromosomes. Chromomycin A₃ (CMA)-positive (+) bands were observed in telomeric positions of four chromosomes in all accessions. 4'-6-diamidino-2-phenylindole (DAPI)-negative bands (−) corresponded with CMA+ bands. Fluorescence in situ hybridization (FISH) was conducted using open-pollinated seedlings of ‘Osa Gold’ (Pyrus pyrifolia) and Toyotomi Nashi (P. mikawana) as materials. Four out of six 18S-5.8S-25S ribosomal RNA gene (rDNA) sites corresponded with CMA+/DAPI− bands. The 5S rDNA sites were detected in centromeric positions of two chromosomes. Two centromeric 5S rDNA and six telomeric 18S-5.8S-25S rDNA sites were located on different chromosomes as determined from the results of multi-color FISH.

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Many species of the Rosaceae family exhibit an S-ribonuclease (S-RNase)-based self-incompatibility (SI) system. In this system, pistil and pollen specificities are conferred by S-RNase and S locus F-box protein, respectively. In addition to these specificity determinants, other SI general factors have been observed to be essential for an SI reaction. To isolate SI general factors in Prunus, yeast two-hybrid (Y2H) screening was performed against the sweet cherry (Prunus avium L.) pollen cDNA library using the N-terminal (NT) and C-terminal (CT) regions of P. avium (Pav) S⁶-RNase as bait. Among 31 genes isolated by Y2H screening, the interaction between actin homolog (PavAct1) and S-RNase was further examined by in vitro assays because some T2/S-type RNase family proteins, such as RNASET2 and ACTIBIND, are assumed to exert their cytotoxicity through its actin-binding ability. Although the GST pull-down assay did not detect any interaction between GST-tagged recombinant PavAct1 and non-reduced S-RNase, interaction between the recombinant PavAct1 and reduced S-RNase was observed. Furthermore, filamentous actin (F-Act) cosedimentation assay and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) crosslinking assay using rabbit actin demonstrated that reduced S-RNases interacted with both F-Act and globular actin (G-Act). These results collectively suggested that S-RNase, which may be fully or partially reduced in the pollen tube cytoplasm, could bind actin to disrupt the coordinated actin dynamics.

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Citrus trees alternate between rich and poor crops and are known to be alternate-bearing crops. Alternate bearing results from suppression of flowering due to bearing of fruits. To understand the molecular mechanism how fruit bearing affects flowering, we investigated the relationship between fruits and a flowering-related gene, citrus FLOWERING LOCUS T (CiFT). On trees with different amounts of fruits, the fruit weight/leaf area ratio at harvest was negatively and highly correlated with CiFT expression in the vegetative shoots during fall and winter, which is the period of floral induction. In addition, CiFT expression levels during fall and winter were positively and highly correlated with the flower number the following spring. These results indicate that fruit growth suppresses CiFT expression and decreases the flower number the next spring. In another experiment conducted to determine the effect of the period of fruit bearing on CiFT expression, trees having 3 primary scaffold branches were analyzed. From each branch in 1 tree, all the flowers or fruits were harvested at different times. In November, CiFT was expressed at different levels in each branch, with a tendency to be low in the stem of vegetative shoots from branches that bore fruits for longer periods. This result indicates that a long fruit-bearing period suppresses CiFT expression in vegetative shoots. CiFT expression was detected at much higher levels in fruit-bearing shoots than in vegetative shoots in September. In January, the high levels of CiFT expression in bearing shoots decreased to levels lower than those found in vegetative shoots. Thus, in fruit-bearing shoots, the CiFT expression of an unknown relationship to floral induction is observed during the period before floral induction and the seasonal change of CiFT expression in fruit-bearing shoots is different from that in vegetative shoots.

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To clarify the differences between white asparagus (Asparagus officinalis L.) spears produced by two different blanching methods, the soil-mound method and film-cover method, the external appearance and hardness of spears were examined in forcing culture with two-year-old rootstocks. The blanching method had an obvious influence on the color and tightness of the spear tip. Color in the portion 2 cm below the spear tip was more yellowish in the film-cover method than in the soil-mound method. The spear tips tended to be tighter in the soil-mound method than in the film-cover method. These results suggest that both the spear tip color and tightness might be striking visible features to help us discriminate between the two blanching methods. Spears produced by the soil-mound method were greater in diameter in the upper (4 cm from tip) and middle (10.5 cm from tip) portions, and heavier by weight than those by the film-cover method. Spears boiled for 10 minutes from the soil-mound method were significantly tougher in the upper (4 cm from tip) and middle (10.5 cm from tip) sections than those from the film-cover. Therefore, the blanching method was thought to affect spear hardness, which is closely associated with eating and cooking quality.

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To determine the relationship between cell size, acid invertase (AI) and sucrose phosphate synthase (SPS) activities, and sucrose accumulation in melon (Cucumis melo L.), fruit were treated with succinamic acid 2,2-dimethylhydrazide (SADH) at various developmental stages during spring and summer. Fruit and cell growth was suppressed by SADH treatment during early, but not middle, development. Higher AI activity and lower SPS activity and sucrose content were observed in fruit with smaller cells exposed to early SADH treatment, compared to fruit with larger cells exposed to late SADH treatment. These results suggest that the low sucrose content in fruit treated with SADH during early fruit development is due to the lower SPS activity of smaller cells resulting from SADH exposure.

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Effects of exogenous gibberellin (GA), gibberellin biosynthesis inhibitors, and abscisic acid (ABA) on rhizome morphogenesis (transition to storage organ) were examined in seed-derived lotus (Nelumbo nucifera Gaertn.) plants. Exogenous 1 mg·L⁻¹ GA₃ promoted rhizome elongation without swelling under short-day conditions, whereas uniconazole with 0.1 mg·L⁻¹ and paclobutrazole with 0.1, 1, and 10 mg·L⁻¹ stimulated rhizome enlargement under long-day conditions. Rhizomes of the plants grown with 10 and 25 mg·L⁻¹ ABA also enlarged under long-day conditions. Rhizome enlargement was closely related to cell enlargement and starch grain accumulation. In all the experiments, starch grain accumulation in expanded cells was recognized in the enlarged rhizomes, but not in the elongated rhizomes. It was suggested that rhizome transition to the storage organ was regulated via biosynthesis of GA and/or ABA.

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In evergreen azalea, unique old mutational cultivars, whose flower have split figure, have been collected and is called “sai-zaki” in Japanese. The morphology of leaves and flowers of the wild-type and sai-zaki cultivars ‘Hanaguruma’, ‘Gin-no-zai’, and ‘Seigaiha’ of R. macrosepalum was investigated. In contrast to the gamopetalous corolla of the wild type, all sai-zaki cultivars formed the choripetalous corolla type, which consisted of 5 independent petals. The width of the leaf, sepal, and petal of all sai-zaki cultivars, except for the sepal of ‘Gin-no-zai’, all tended to be narrower than the wild type; in particular, all lateral organs of ‘Seigaiha’ were extremely narrow compared with the wild type. In contrast to the normal pistil of the wild type, ‘Hanaguruma’ and ‘Gin-no-zai’, normal and malformed pistils we’re observed in ‘Seigaiha’. Epidermal cell size was not related to the narrowness of lateral organs in the wild-type and sai-zaki cultivars. These results indicate that the sai-zaki trait of materials, at least ‘Seigaiha’, would be a common mutation in the growth of lateral organs in the transverse plane. All sai-zaki cultivars showed fertility. The sai-zaki trait of old Japanese cultivars from the Edo era is expected to provide new breeding material that offers the opportunity to generate additional morphological novelties.

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Lilium longiflorum is endemic to the islands of the Ryukyu Archipelago in Japan and to the eastern seacoasts and satellite islands of the mainland of Taiwan. The species is an important ornamental plant, and is cultivated throughout the world. Lilium longiflorum has long been regarded as a self-incompatible species but the existence of selfing in some natural populations was suggested by isozyme analysis in a previous study. To confirm the occurrence of self-compatible individuals and to clarify the evolutionary shift of floral traits associated with degree of self-compatibility in L. longiflorum by comparative analysis, we used 17 populations of L. longiflorum, and two populations of L. formosanum, the genetically closest species of L. longiflorum, covering the entire species distribution. Artificial self-pollination revealed that not all L. longiflorum individuals are self-incompatible and there is substantial quantitative variation of self-incompatibility among L. longiflorum individuals and populations. Self-compatible dominant populations allopatrically and independently evolved at the periphery of the species distribution area, the northern Ryukyu Archipelago and Taiwan. Increasing degree of self-compatibility in L. longiflorum correlated with reduced corolla length, corolla width, corolla volume, and anther length for the Ryukyu Archipelago, in contrast to only reduced corolla width and volume for Taiwan. Approach between anther and stigma was not observed in any populations. Our data indicate that in the Ryukyu Archipelago increasing degree of self-compatibility evolved floral traits related to mating system evolution, to selfing, that does not depend on adjacency between anther and stigma position, but not in Taiwan.

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The flower colors and anthocyanin constitution of eight cultivars of Vintage series bedding Stock (Matthiola incana) were surveyed to determine the relation between their flower colors and anthocyanin components. Thirteen anthocyanins were isolated from the flowers of these cultivars as major anthocyanins, and their structures were identified by chemical and spectroscopic techniques. Among them, a novel anthocyanin, cyanidin 3-caffeoyl-sambubioside-5-malonyl-glucoside (pigment 1) was found in single and double flowers in cultivars of ‘Vintage Lavender’ and ‘Vintage Burgundy’. Furthermore, two anthocyanins, cyanidin 3-p-coumaroyl-sambubioside-5-malonyl-glucoside (pigment 2) and cyanidin 3-feruloyl-sambubioside-5-malonyl-glucoside (pigment 3), were also found in these cultivars for the first time in Matthiola incana flowers. Regarding the flower color variation in these cultivars, the hue values (b*/a*) of these flower colors were roughly responsible for the numbers of hydroxycinnamic acid residues in anthocyanin molecules and also hydroxyl patterns of the B-ring in anthocyanidins. These flower colors were classified into eight groups, A–H, based on the hue values of their flowers, and were arranged as follows. In violet flowers (hue values b*/a* = −0.66 and −0.69, V 84A) of group A, cyanidin 3-dihydroxycinnamoyl-sambubioside-5-malonyl-glucosides were major anthocyanin pigments. In purple flowers (−0.43 and −0.45, P 75A) and red-purple flowers (−0.14 and −0.16, RP 74A) of groups B and D, pelargonidin 3-dihydroxycinnamoyl-sambubioside-5-malonyl-glucosides were major anthocyanin pigments. In red-purple flowers (−0.21 and −0.24, RP 72A) of group C, cyanidin 3-monohydroxycinnamoyl-sambubioside-5-malonyl-glucosides were major anthocyanin pigments. In red flowers (0.05 and 0.06, RP 66A) of group E, pelargonidin 3-monohydroxycinnamoyl-sambubioside-5-malonyl-glucosides were major anthocyanin pigments. In copper (0.23 and 0.16, R 54A) and peach (2.37 and 2.09, R38C) of groups F and G, pelargonidin 3-glucoside was a major anthocyanin pigment, and a small amount of pelargonidin 3-glucoside was present in yellow flowers of group H. From these results, the relation between flower colors and the bluing effects of acylated anthocyanins with hydroxycinnamic acids was discussed in flowers of Matthiola incana cultivars of Vintage series.

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Flower-bud blasting is a constraint for producing Eustoma grandiflorum so a preventative strategy is needed. Flower-bud blasting occurs under low light intensity and high fertilizer input. To gain insight into the mechanisms of flower-bud blasting, we conducted a detailed characterization of flower development under normal and blast-inducing conditions. We found that floral buds under low light intensity ceased to grow at the stamen and gynoecium differentiation stages, although sepals and petals were initiated normally. Aborted flowers rarely had normal ovules. Moreover, an expanded apical meristem was observed. These results show that the differentiation and development of reproductive organs are critically suppressed by blast-inducing conditions; however, combined application of 300 ppm benzylaminopurine and 200 ppm gibberellic acid-3 to floral buds resulted in about five-fold greater frequency of flower opening compared to controls. Blasting inhibition also resulted from excising the inflorescent branch, suggesting the decrease in assimilates in flower buds would be attributed to flower-bud blasting. Moreover, hormone application combined with excision had an additive effect for preventing flower-bud blasting, suggesting that these treatments independently inhibit flower-bud blasting. These results suggest that flower-bud blasting in Eustoma is a break in floral development around the stamen and gynoecium initiation stages and is integrally induced by the factors related to hormone biosynthesis and the decrease in assimilates.

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L-ascorbate (ASA; a reduced form of vitamin C) and glutathione (GSH) in tomato fruit participate in many diverse biological processes such as fruit ripening. In general, ASA and GSH are regulated by the reactive oxygen species scavenging system (antioxidant system). The tomato is a complex fruit composed of skin, pericarp walls, placenta, locular tissue, and seed tissues, and it is unclear whether the antioxidant contents and systems differ among these tissues. The aim of this study is to clarify tissue-specific changes in oxidative parameters, antioxidant contents, and antioxidant enzymes during fruit ripening in the tomato pericarp (skin, pericarp walls) and pulp (placenta, locular tissue, seeds). Lipid peroxidation and the H₂O₂ content remained constant during fruit ripening and were lower in the pulp than in the pericarp. In addition, ASA and GSH contents were the same in both these tissues when the fruits were picked at the red stage; however, changes in the superoxide dismutase, catalase, and ASA–GSH cycles, related to enzymes such as ascorbate peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase, showed tissue-specific differences during ripening. These results indicate that ASA and GSH contents in both tissues are the same when fruits are picked at the red stage, but oxidative parameters and antioxidant systems show tissue-specific differences during fruit ripening. Furthermore, our results indicate that oxidative stress in the pulp was lower than that in the pericarp. This work therefore provides a basis for understanding the role of antioxidant systems during tomato fruit ripening.

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Free radical formation from flavonoids by peroxidase action and changes in flavonoid levels and peroxidase activity during storage were determined to clarify the involvement of naringin radical in chlorophyll (Chl) degradation in stored green Nagato-yuzukichi (Citrus nagato-yuzukichi hort. ex Y. Tanaka) fruit. Chl a was degraded by peroxidase-hydrogen peroxide system not in the presence of hesperidin but with naringin. However, radical formation of both naringin and hesperidin, which were the main flavonoids in the flavedo of Nagato-yuzukichi fruit, with peroxidase-mediated oxidation was found by electron spin resonance analysis. The naringin radical, which was formed by a radical forming reagent, potassium ferricyanide, was related to the formation of 13²-hydroxychlorophyll (OHChl) with Chl a degradation, whereas the hesperidin radical hardly affected OHChl a formation. In addition, superoxide dismutase did not inhibit Chl a degradation by naringin radical formed by potassium ferricyanide. In Nagato-yuzukichi fruit, Chl-degrading peroxidase activity increased considerably during storage at 20°C, with a peak value on day 6 of storage in accordance with decrease in Chl content, after which it decreased. The contents of naringin and hesperidin, especially the former, decreased during storage at 20°C, but afterwards increased slightly. These findings suggest that the naringin radical formed by peroxidase could be partly involved in Chl degradation during storage in Nagato-yuzukichi fruit.

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