., 2006 ; Lingle and Dunlap, 1987 ; Schaffer et al., 1987 ; Winter and Huber, 2000 ). It was reported that both acid invertase (EC 126.96.36.199) and sucrose phosphate synthase (EC 188.8.131.52) are determinants of sucrose accumulation in melon fruit. However
Xiyan Yu, Xiufeng Wang, Jide Fan, Hongmei Tian, and Chengchao Zheng
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
Jun Matsumoto, Hideyuki Goto, Yasutaka Kano, Akira Kikuchi, Hideaki Ueda, and Yuta Nakatsubo
measured by the Mutarotase-GOD method ( Miwa et al., 1972 ). Sucrose phosphate synthase assay. Two hundred microliters of supernatant was dialyzed twice for 30 min against 200 mL of 10 m m Mops-NaOH by oscillatory microdialysis system (Cosmo Bio, Tokyo
Gene Lester, Luis Saucedo Arias, and Miguel Gomez-Lim
Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is the single most important consumer preference attribute. During fruit ripening, sucrose accumulates when soluble acid invertase (AI) activity is less then sucrose phosphate synthase (SPS) activity. To genetically heighten fruit sugar content, knowledge of sugar accumulation during fruit development in conjunction with AI and SPS enzyme activities and their peptide immunodetection profiles is needed. Two netted muskmelon cultivars [`Valley Gold' (VG), a high sugar accumulator, and `North Star' (NS), a low sugar accumulator] with similar maturity indices were assayed for fruit sugars, AI, and SPS activity and immunodetection of AI and SPS polypeptides following 2, 5, 10, 15, 20, 25, 30, 35, and 40 (abscission) days after anthesis (DAA). Both cultivars, grown in spring and fall, showed similar total sugar accumulation profiles. Total sugars increased 1.5 fold, from 2 through 5 DAA and then remained unchanged until 30 DAA. From 30 DAA until abscission, total sugar content increased, with VG accumulating significantly more sugar then NS. In both cultivars, during both seasons, sucrose was detected at 2 DAA, which coincided with higher SPS activity than AI activity. At 5 through 25 DAA, SPS activity was less then AI activity resulting in little or no sucrose detection. It was not until 30 DAA that SPS activity was greater than AI activity resulting in increased sucrose accumulation. VG at abscission had higher total sugar content and SPS activity and lower AI activity than NS. Total polypeptides from both cultivars 2 through 40 DAA, were immunodetected with antibodies: anti-AI and anti-SPS. NS had Al isoforms bands at 75, 52, 38, and 25 kDa that generally decreased wtih DAA. One isoform at 52 kDa remained detectable up to anthesis (40 DAA) VG had the same four Al isoforms, all decreased with DAA and became undetectable by 20 DAA. It is unclear if one or all AI isoforms correspond with detected enzyme activity. VG and NS had one SPS band at 58 kDa that increased with DAA and concomitantly with SPS activity. VG had a more intense SPS polypeptide band at abscission then did NS. Thus, netted muskmelon sugar accumulation may be increased by selecting for cultivars with a specific number of AI isoforms, which are down-regulated, and with high SPS activity during fruit ripening.
Gene E. Lester, Luis Saucedo Arias, and Miguel Gomez-Lim
Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is the single most important consumer preference attribute. During fruit ripening, sucrose accumulates when soluble acid invertase (AI) activity is less then sucrose phosphate synthase (SPS) activity. To genetically heighten fruit sugar content, knowledge of sugar accumulation during fruit development in conjunction with AI and SPS enzyme activities and their peptide immunodetection profiles, is needed. Two netted muskmelon cultivars, Valley Gold a high sugar accumulator, and North Star a low sugar accumulator, with identical maturity indices were assayed for fruit sugars, AI and SPS activity, and immunodetection of AI and SPS polypeptides 2, 5, 10, 15, 20, 25, 30, 35, or 40 (abscission) days after anthesis (DAA). Both cultivars, grown in the Fall, 1998 and Spring, 1999, showed similar total sugar accumulation profiles. Total sugars increased 1.5 fold, from 2 through 5 DAA, then remained unchanged until 30 DAA. From 30 DAA until abscission, total sugar content increased, with `Valley Gold' accumulating significantly more than `North Star'. During both seasons, sucrose was detected at 2 DAA, which coincided with SPS activity higher than AI activity, at 5 through 25 DAA, no sucrose was detected which coincided with SPS activity less than AI activity. At 30 DAA when SPS activity was greater than AI activity, increased sucrose accumulation occurred. `Valley Gold' at abscission had higher total sugar content and SPS activity, and lower AI activity than `North Star'. `North Star' had AI isoforms at 75, 52, 38, and 25 kDa (ku) that generally decreased with maturation, although the isoform at 52 ku remained detectable up to anthesis (40 DAA). `Valley Gold' had the same four AI isoforms, all decreased with maturation and became undetectable by 20 DAA. Both `Valley Gold' and `North Star' had one SPS band at 58 ku that increased with DAA, and coincided with SPS activity. `Valley Gold' had a more intense SPS polypeptide band at abscission than `North Star'. Thus, netted muskmelon fruit sugar accumulation may be increased, either by genetic manipulation or by selecting for cultivars with a specific number of down-regulated AI isoforms, and higher SPS activity during fruit ripening.
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.
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.
Natalie L. Hubbard, D. Mason Pharr, and Steven C. Huber
Abbreviations: CER, net carbon exchange rate; DAA, days after an thesis; SPS, sucrose phosphate synthase. Cooperative investigation of the North Carolina Agricultural Research Service, U.S. Dept. of Agriculture, and Agricultural Research Service
Yosef Burger and Arthur A. Schaffer
Schaffer, 1991 ; Stommel, 1992 ; Yelle et al., 1991 ). A key role for sucrose phosphate synthase (SPS) activity in sucrose-accumulating melon fruit was proposed by Hubbard et al. (1991) , who showed that sucrose accumulation in melon fruit was
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