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Takaya Moriguchi, Kazuyuki Abe, Tetsuro Sanada, and Shohei Yamaki

Abbreviations: DTT, dithiothreitol; NAD+-SDH, NAD+-dependent sorbitol dehydrogenase; SPS, sucrose-phosphate synthase; SS, sucrose synthase. 1 Present address: Laboratory of Horticulture, School of Agriculture, Nagoya Univ., Chikusa, Nagoya, 464

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Charmara Illeperuma, Donald Schlimme, and Theophanes Solomos

Potato tubers (Solanum tuberosum `Russet Burbank') were stored at 1 °C in air for 28 days and then transferred to 10 °C in either air or 2.53 kPa O2. During cold storage there was an increase in sucrose, glucose, and fructose. The activities of extractable sucrose phosphate synthase (SPS) and invertase increased by 2.2- and 7.7-fold, respectively, during 28 days at 1 °C. The activity of sucrose synthase (SS) remained constant at 1 °C and was similar to that found in tubers kept continuously at 10 °C. With the transfer of tubers from 1 to 10 °C, there was an initial sharp rise in respiration which peaked at ≈7 days, followed by a gradual decline. Sucrose declined rapidly during reconditioning, while glucose and fructose declined more slowly. With the transfer of tubers from 1 to 10 °C, the activity of SS increased sharply after 7 days at 10 °C, to be followed by a decline to the levels found in control tubers. The activities of both extractable SPS and invertase decreased during reconditioning, reaching the values of the control tubers within ≈15 days. Low O2 inhibited the decrease in sugars and suppressed the rise in SS activity, but it did not alter the decrease in SPS and invertase. Western blot analysis showed that the amount of SPS protein remained unchanged at 1 and 10 °C. These results indicate that the activity of SPS is regulated by factors other than the amount of its protein. The activities of the above three enzymes showed no changes in tubers kept at 10 °C continuously. In control tubers SPS showed the highest activity, followed by SS and invertase.

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Heeock Boo, Honggi Kim, and Hyunhwa Lee

carbohydrate metabolism. Sucrose synthase (SS) and sucrose phosphate synthase (SPS) are enzymes that affect sucrose metabolism and that are associated with the developmental processes of the sink organ ( Balibrea et al., 1996 ; Islam et al., 1996 ; Kim et al

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Md. Shahidul Islam, S. Khan, and T. Matsui

Sucrose metabolism was followed in developing fruit of domesticated cherry tomato (Lycopersicon esculentum var. cerasiforme Alef.). The high amounts of reducing sugars were consistently linked to high soluble acid invertase (EC, whereas sucrose synthase (EC followed the same pattern of sucrose levels and reached a peak of activity during early stage of maturation and then decreased to near nil. In comparison, sucrose phosphate synthase (EC activity remain relatively constant throughout development. Thus, sucrose synthase and acid invertase, rather than sucrose phosphate synthase, are the critical enzymes regulating sucrose accumulation in tomatoes. Cultivated cherry tomato sucrose synthase (UDP-glucose: D-fructose 2-glucosyltransferase) was purified to homogeneity by ammonium sulfate precipitation, anion exchange chromatography on DEAE-Toyopreal 650, and gel filtration on Sephadex G-200. Further purification to homogeneity resulted from a single band from SDS-PAGE. The enzyme was identified as a homotetramer with a total molecular mass of 370 kDa and subunits of 92 kDa. The enzyme showed maximum activity for the cleavage and synthesis of sucrose was at pH 7.0 and 8.0, respectively, and the optimum temperature was 40°C in both directions for HEPES-KOH buffer. The enzymatic reaction followed typical Michaelis–Menten kinetics, with the following parameters: Km (fructose),7.4; Km (UDP-glucose), 0.2612; Km (sucrose), 33.24; Km (UDP), 0.0946. The enzyme was very sensitive to inhibition by heavy metals.

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Akio Suzuki, Yoshinori Kanayama, and Shohei Yamaki

The properties of sucrose synthase (SS) isozymes partially purified from immature fruit (SS I) of Japanese pear (Pyrus serotina Rehder var. culta Rehder) were different than those of mature fruit (SS II). A clear difference in elusion pattern during DEAE-cellulose chromatography was observed, although the apparent molecular weight of the native proteins extracted from both stages was 350 kD. The Km value of SS II for UDP was similar to that for UDP-glucose; while with SS I, the Km for UDP was lower than that for UDP-glucose. This suggests that SS II activity favors sucrose synthesis compared with SS I, which favors sucrose cleavage. The optimum pH for activity toward sucrose synthesis was 8.0 for SS II and 8.5 to 9.5 for SS I. SS II from mature fruit may be an isozyme of SS occurring during periods of rapid sucrose accumulation, while SS I from immature fruit is more similar to the typical SS which functions mainly toward sucrose cleavage in many plants.

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Yanwen Gong and Theophanes Solomos

Previous research has shown that subjecting bananas to low O2 treatment during the climacteric rise decreases the rate of sugar accumulation but the fruits eventually ripen. In the present study we applied low O2 in fruits whose ripening had been initiated by exogenous C2H4 and in preclimacteric ones. In preclimacteric fruits low O2 suppressed the climacteric rise during the duration of the experiment (20 days). It completely inhibited the increase in sugars, invertase and sucrose phosphate synthase (SPS) activities while there was a sharp increase in sucrose synthase (SS). In control fruits the increase in sugar content coincides with a sharp increase in invertase, and SPS and a decline in SS. Hypoxia inhibited the increase in invertase and SPS while it induced an increase in SS. Nevertheless, the activities of invertase and SPS in the climacteric hypoxic fruits was higher than in hypoxic preclimacteric ones. The results, thus, indicate that the imposition of low O2 at the preclimacteric stage is much more efficient in delaying banana ripening than when it is applied after the initiation of ripening.

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Yosef Burger and Arthur A. Schaffer

sucrose synthase ( Giaquinta, 1979 ; Moriguchi, et al., 1990 , 1992 ; Schaffer et al., 1987 ; Suzuki et al., 1996 ) and neutral, or alkaline, invertase ( Glasziou and Gayler, 1972 ; Kato and Kubota, 1978 ; Ricardo and Rees, 1970 ) activities have

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Jinmin Fu, Bingru Huang, and Jack Fry

, understanding the enzyme activity affecting sucrose metabolism is critical. Sucrose synthesis can be regulated by rapid changes in the activity of sucrose phosphate synthase, sucrose synthase, and acid invertase ( Castrillo, 1992 ; Hawker, 1985 ; Huber and

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Hui-juan Zhou, Xia-nan Zhang, Ming-shen Su, Ji-hong Du, Xiong-wei Li, and Zheng-wen Ye

., 2010 ). The main soluble sugars in peaches are sucrose, fructose, glucose, and sorbitol, which are regulated by vacuolar acid invertase (AI), neutral invertase (NI), sucrose phosphate synthase (SPS), and sucrose synthase (SS) ( Bianco and Rieger, 2002

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Kurt D. Nolte, Gregory W. Erdos, and Karen E. Koch

Localization of sucrose synthasa (SS), an enzyme Previously shown to be highly active in transport tissues of citrus fruit, was further defined via immunohistochemical analysis of stage II calamondin fruit. Using the indirect immunogold technique, 8 μm sections were first reacted with rabbit anti-SS polyclonal serum followed by incubation with 5 nm gold conjugated goat-anti-rabbit IgG. Little immunolabel was observed in the majority of peel tissues, however an abundant immunoreaction was evident in parenchyma cells directly adjacent to the segment epidermis surrounding juice sacs. Antibody was not associated with this epidermnl layer. Similarly, in juice vesicle stalks (JVS) the internal parenchyma cells showed significant SS localization compared to minimal immunoreaction in the epidermal layers of the JVS. Although the antigen did not appear to be specifically localized within the vascular bundles, an extensive distribution of the enzyme was associated with the parenchymatous cells immediately adjacent to vascular strands.