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Satoru Kondo and Yusuke Takano

Effects of the synthetic auxin 2,4-DP on fruit ripening of `La France' pear (Pyrus communis L.) on `Quince C' (Cydonia oblonga Mill. rootstock) were investigated. A solution of 2,4-DP at 90 μL·L-1 was applied 143, 151, and 159 days after full bloom (DAFB) to whole trees and compared with nonstored nontreated fruit and stored nontreated fruit (harvested 165 DAFB). Internal ethylene concentration in 2,4-DP-treated fruit increased more than in nonstored nontreated fruit and the level was higher the earlier the application time. Fruit firmness decreased earliest for fruit treated with 2,4-DP at 143 DAFB, followed by 151 DAFB-treated fruit and then 159 DAFB-treated fruit. In the nonstored nontreated fruit, firmness also showed a slight decrease with time. In all 2,4-DP treatments, water-soluble polyuronide (WSP) increased with ripening and hexametaphosphate-soluble polyuronide (HMP) and HCl-soluble polyuronide (HP) concentrations decreased. Most notably, WSP concentration increased earliest in fruit treated with 2,4-DP at 143 DAFB. Total concentration of neutral sugars from cell walls in each treatment decreased with time, and the levels in fruit treated with 2,4-DP at 143 DAFB were lowest at each sampling time. Arabinose concentrations were high compared with other neutral sugars throughout fruit ripening for each treatment, while glucose concentrations were high in nonripened fruit. At 193 DAFB, ≈85% of the fruit treated with 2,4-DP at 143 DAFB reached edible condition (firmness not more than 0.4 N·mm-2) on the tree. Furthermore, ≈85% of the fruit treated with 2,4-DP at 151 DAFB reached edible condition on 200 DAFB and close to 100% of the fruit treated with 2,4-DP at 159 DAFB on 207 DAFB. When ripened in a controlled room at 20 °C and 90% relative humidity after 2,4-DP treatment, the fruit treated earliest reached edible condition the soonest. Results demonstrate that 2,4-DP treatment can be used as an effective method of producing good quality fruit ripened on the tree, and that 2,4-DP may be an adequate replacement for cold storage conditioning to induce ripening capacity. Chemical name used: 2,4-dichlorophenoxy-propionic acid (2,4-DP).

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Satoru Kondo and Mako Kawai

Free and conjugated abscisic acid (ABA), anthocyanin and sugar concentrations were investigated in the skin of seedless `Pione' grapes (Vitis spp) treated with gibberellic acid (GA) and seeded `Pione' grapes. Seeded fruit were firmer than seedless fruit, until 53 days after full bloom (DAFB). The firmness of seeded fruit decreased dramatically between 43 and 53 DAFB. Anthocyanin concentrations increased in both types of fruit after 53 DAFB, but the concentration in seeded fruit was higher than in seedless fruit. Sugar concentration in the skin was higher in seedless than in seeded fruit prior to 53 DAFB, but at 80 DAFB sugar concentration was higher in the seeded fruit. ABA (free and conjugated forms) concentration in the skin showed a general increase towards harvest (80 DAFB). Skin ABA was higher in seeded than seedless fruit. After cis, trans-ABA (s-ABA) in the skin reached a maximum on 62 or 71 DAFB, its level decreased in both seeded and seedless fruit. The levels of trans, trans-ABA (t-ABA) and conjugated forms in both types of fruit failed to increase or increased only marginally after 62 or 71 DAFB. Free and conjugated ABA in the seed increased with DAFB until harvest. These results suggest that although maturation was promoted initially in the GA-treated seedless fruit, after 53 DAFB it was slowed relative to the seeded fruit. Enhanced maturation during the later stages of development of seeded fruit could be attributed to an increase in ABA concentration in the skin and the seed. These results also demonstrate that s-ABA is not metabolized in the skin to t-ABA and conjugated forms.

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Satoru Kondo, Kazuhiro Settsu and Anan Jitratham

The effective applications of synthetic auxin 2,4-DP on fruit ripening of `La France' pears (Pyrus communis L.) were examined. A solution of 90 μL·L-1 2, 4-DP was applied to fruit and leaves around the fruit as follows: Early 1 = 140 days after full bloom (DAFB); Early 2 = 140 and 150 DAFB; Late 1 = 150 DAFB; and Late 2 = 150 and 160 DAFB. The effects were compared with nontreated fruit. Internal ethylene concentrations increased earliest and rapidly in Early 2 followed by Early 1. Fruit firmness decreased earliest in Early 2 and Early 1. Water-soluble polyuronide (WSP) concentrations in Early 2 were higher than other treatments, but hexametaphosphate-soluble polyuronide (HMP) and cellulose concentrations were lower. At 200 DAFB, 40% of fruit in Early 2 reached edible condition on the tree. In addition, the fruit in Early 2 required shorter periods of time to reach edible condition in a controlled room at 20 °C after harvest of 170, 180, 190, and 200 DAFB. These results show that two 2,4-DP applications at 140 and 150 DAFB may be effective in inducing the ripening capacity of `La France' pears on the tree. Chemical name used: 2-(2,4-dichlorophenoxy)-propionic acid (2,4-DP).

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Satoru Kondo, Hiroko Yamada and Sutthiwal Setha

The effects of n-propyl dihydrojasmonate (PDJ), which is a jasmonic acid derivative, on 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase activities, their gene expressions, and ethylene productions in ‘La France’ pears (Pyrus communis L.) were investigated. The fruit was harvested 156 days after full bloom, stored at 4 °C for 15 days, ripened at 20 °C, and then dipped into 0.39 mm PDJ solution at the preclimacteric stage (0 day of ripening at 20 °C) or the climacteric stage (9 days of ripening at 20 °C). In the skin of the PDJ-treated fruit at the preclimacteric stage, the expressions of ACC synthase (ACS)1 and ACC oxidase (ACO)1 were higher than the expressions of those in the untreated control. Ethylene production also increased in the PDJ-treated fruit. In contrast, the accumulation of the ACS1 messenger RNA (mRNA) levels in the skin and an increase of ethylene production were observed in the untreated control fruit at the climacteric stage, although the levels of mRNAs hybridized with ACO1 were not different between the PDJ-treated fruit and untreated control. The endogenous jasmonic acid levels in the skin increased in the PDJ-treated fruit regardless of the application times of PDJ. These results indicate that ACS1 may be an ACC synthase gene that is induced by jasmonates in pears, and that system 2 ethylene may be regulated by jasmonates.

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Satoru Kondo, Akihiro Tomiyama and Hideharu Seto

Trans-jasmonic acid (JA), cis-JA, and trans-methyl jasmonate (MeJA) were quantified in pulp and seeds of `Tsugaru' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] and `Satohnishiki' sweet cherry (Prunus avium L.). Trans-JA and cis-JA showed similar changes during development in both types of fruit. JA concentration was high in the early growth stages of apple pulp development, decreased with days after full bloom (DAFB), and then increased again during maturation. There was an initial decrease in concentration of MeJA in apple pulp, followed by a general increase towards harvest. Concentrations of JA and MeJA in the pulp of sweet cherry were high during early growth stages, then decreased towards harvest. PDJ treatment at 104 DAFB (preclimacteric stage) increased endogenous abscisic acid concentration and anthocyanin concentration at 122 and 131 DAFB (maturation stages) in apple. JA concentration in apple seeds was also high in the early growth stages, then decreased, and finally peaked at harvest. MeJA concentration in apple seeds increased towards harvest. In the seeds of sweet cherry, JA and MeJA concentrations generally increased until harvest. In both types of fruit, concentrations of JA and MeJA in the seeds were higher than those of pulp. On a dry weight basis, changes in concentration in the seeds preceded those in the pulp. These results demonstrate that relatively high amounts of JA and MeJA are associated with young developing fruit. These substances may have a role in regulation of fruit growth at early growth stages, though this has not been demonstrated. Chemical name used: n-propyl dihydrojasmonate (PDJ).

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Satoru Kondo, Anan Jitratham, Monrudee Kittikorn and Sirichai Kanlayanarat

Effects of low temperature and chilling injury (CI) on jasmonic acid (JA) and methyl jasmonate (MeJA) concentrations were investigated in mangosteens (Garcinia mangostana L.). JA concentrations in the skin of fruit stored at 7 °C increased significantly compared with that of those stored at 13 °C, but JA decreased with the occurrence of visible symptoms of CI. Neither an increase in JA nor CI was detected in pulp of fruit stored at 7 °C. JA concentrations in the skin of fruit treated with spermine (Spm) and stored at 7 °C also increased, but at a lesser extent than in untreated fruit. Thus, the response of JA to low temperatures appears to be limited to chill-susceptible parts of the fruit. The decrease of JA and the onset of CI was delayed in fruit treated with Spm kept at 7 °C compared with untreated control fruit. Exogenous application of n-propyl dihydrojasmonate, which is a jasmonic acid derivative, effectively decreased CI. These results suggest that low temperature-induced JA accumulation may play a protective role against CI. The application of jasmonates may increase chill-resistance in fruit.

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Satoru Kondo, Wanvisa Ponrod, Sirichai Kanlayanarat and Nobuhiro Hirai

Endogenous abscisic acid (ABA), its 2-trans isomer (trans-ABA), phaseic acid (PA), and dihydrophaseic acid (DPA) concentrations were quantified in the peel, aril, and seed of mangosteen (Garcinia mangostana L.). Changes in carbon dioxide (CO2) and ethylene (C2H4) production and 1-aminocyclopropane-1-carboxylic acid (ACC) concentration in the peel and aril were also examined. ACC concentration and CO2 and C2H4 production were high at the beginning of fruit development and gradually decreased toward harvest, which confirms that mangosteen is a nonclimacteric fruit. In the peel and aril, the increase in ABA concentration preceded the decrease in peel firmness and coloring of the peel. This suggests that ABA may induce the maturation of mangosteens. The state of ABA metabolism varied with the part of fruit. In the peel, PA and DPA were not considered to be predominant metabolites of ABA because their concentrations were low compared to ABA throughout fruit development. In contrast, in the aril and seed, it is possible that the PA-DPA pathway may be a main pathway of ABA metabolism because the concentrations of DPA in the aril and of PA in the seed directly coincided with the concentrations of ABA. The differences in the ABA metabolites between aril and seed may be caused by the rate of ABA metabolism. The concentrations of ABA and its metabolite in the seed decreased toward harvest.

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Satoru Kondo, Kentaro Hiraoka, Shozo Kobayashi, Chikako Honda and Norihiko Terahara

Cyanidin 3-galactoside was the primary anthocyanin in red `Tsugaru' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. The concentration of cyanidin 3-galactoside in the skin decreased from 20 to 62 days after full bloom (DAFB), then increased rapidly after 104 DAFB. Small amounts of cyanidin 3-arabinoside and cyanidin 3-glucoside were detected at 122 and 133 DAFB (harvest). The expression of five anthocyanin biosynthetic genes of chalcone synthase (MdCHS), flavanone 3-hydroxylase (MdF3H), dihydroflavonol 4-reductase (pDFR), anthocyanidin synthase (MdANS), and UDP glucose-flavonoid 3-O-glucosyltransferase (pUFGluT) was examined in the skin of red and nonred apples. In general, the expression of anthocyanin biosynthetic genes in red apples was strong in juvenile and ripening stages. The expression of MdCHS, MdF3H, pDFR, and MdANS was observed before ripening stage when anthocyanin was not detected. In contrast, the expression of pUFGluT was detected in the development stage only when anthocyanin was detected. However, the expression of all five genes was observed at 20 DAFB in fruit bagged after fertilization, and anthocyanin was not detected. The expression of MdCHS, MdF3H, pDFR, and MdANS, excluding pUFGluT, was detected at 98 DAFB in fruit bagged after 30 DAFB, and anthocyanin was not detected. These results suggest that pUFGluT may be closely related to the anthocyanin expression in apple skin at the ripening stage.

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Satoru Kondo, Futoshi Yazama, Kasinee Sungcome, Sirichai Kanlayanarat and Hideharu Seto

Jasmonic acid (JA) and methyl jasmonate (MeJA) were quantified in the skin, pulp, and seeds of `Nam Dok Mai' and `Nang Klangwan' mangoes (Mangifera indica L.). JA showed similar changes during development in both cultivars of fruit. JA concentrations were high in the early growth stages of skin and pulp development, decreased with days after full bloom (DAFB), and then increased again during ripening. JA concentrations in the skin were higher than those in the pulp. 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations in the skin and pulp of both cultivars increased toward harvest. Differing with JA, ACC concentrations in the pulp were high compared with the skin. This fact suggests that although JA and ACC are associated with the ripening of mangoes, they may play different roles. JA concentrations in the seeds of both cultivars decreased toward harvest, possibly suggesting a lack of dormancy in mango seeds. Changes in jasmonates during storage were also examined. JA content in the skin and pulp increased in stored fruit. In addition, the increase in JA content was largest in fruit that lost the most fresh weight. This suggests that JA accumulation that occurs during fruit senescence is associated with moisture loss.

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Monrudee Kittikorn, Katsuya Okawa, Hitoshi Ohara, Satoru Kondo, Nobuhiro Kotoda, Masato Wada, Mineyuki Yokoyama, Ohji Ifuku, Ariake Murata and Naoharu Watanabe

Changes of endogenous 9, 10-ketol-octadecadienoic acid (KODA) concentrations, which is synthesized from linolenic acid by 9-lipoxygenase, were analyzed in apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] buds. In addition, the effects of 15, 16-chloro, hydroxy-9-hydroxy-10-oxo-12(Z)-octadecenoic acid (CKODA) application, which is an analog of KODA, on flower bud formation and the expression of MdTFL1 (terminal flower 1) and MdFT1 (flowering locus t 1) genes in apple buds were investigated in heavy-crop treatment (HCT) and under shade. An increase of endogenous KODA in the buds in the fruit-thinning treatment, which resulted in a higher proportion of flower bud formation than in HCT, was observed at 63 days after full bloom, but no such increase was found in HCT. In the shade-treated and heavy-crop trees, the expression of MdTFL1 in the buds to which CKODA was applied was lower than that in untreated buds. In contrast, under shade, the expression of MdFT1 in the CKODA-treated buds was higher than that in untreated buds. These results suggest that endogenous KODA may be associated with flower bud formation, and its application may be effective at improving the proportion of flower bud formation through its effect on MdTFL1 and MdFT1.