No abstract

A number of basic leucine zipper (bZIP) transcription factors are known to function in stress signaling in plants but few have thus far been functionally characterized in rice. In our current study in rice, we have newly isolated and characterized the OsABF1 (Oryza sativa ABA responsive element binding factor 1) gene that encodes a bZIP transcription factor. Its expression in seedling shoots and roots was found to be induced by various abiotic stress treatments such as anoxia, salinity, drought, oxidative stress, cold and abscisic acid (ABA). Subcellular localization analysis in maize protoplasts using GFP fusion vectors indicated that OsABF1 is a nuclear protein. In a yeast experiment, OsABF1 was shown to bind to ABA responsive elements (ABREs) and its N-terminal region was necessary to transactivate the downstream reporter gene. The homozygous T-DNA insertional mutants Osabf1-1 and Osabf1-2 were more sensitive in response to drought and salinity treatments than wild type plants. Furthermore, the upregulated expression of some ABA/stress-regulated genes in response to ABA treatment was suppressed in these Osabf1 mutants. Our current results thus suggest that OsABF1 is involved in abiotic stress responses and ABA signaling in rice.

The noncharacterized gene previously proposed as the D-tagatose 3-epimerase gene from Agrobacterium tumefaciens was cloned and expressed in Escherichia coli. The expressed enzyme was purified by three-step chromatography with a final specific activity of 8.89 U/mg. The molecular mass of the purified protein was estimated to be 132 kDa of four identical subunits. Mn 2؉ significantly increased the epimerization rate from D-fructose to D-psicose. The enzyme exhibited maximal activity at 50°C and pH 8.0 with Mn 2؉ . The turnover number (k cat ) and catalytic efficiency (k cat /K m ) of the enzyme for D-psicose were markedly higher than those for D-tagatose, suggesting that the enzyme is not D-tagatose 3-epimerase but D-psicose 3-epimerase. The equilibrium ratio between D-psicose and D-fructose was 32:68 at 30°C. D-Psicose was produced at 230 g/liter from 700-g/liter D-fructose at 50°C after 100 min, corresponding to a conversion yield of 32.9%.The International Society of Rare Sugars defines rare sugars as monosaccharides and their derivatives that rarely exist in nature. According to this definition, D-psicose is a rare sugar. Rare sugars have recently attracted much attention due to their many uses, including uses as low-calorie sweeteners and bulking agents (11,12,14,17,18), as immunosuppressants in allogeneic orthotopic liver transplantation in rats (6), as potential inhibitors of various glycosidases (20), in ischemiareperfusion injury of the rat liver (5), and in segmented neutrophil production without other detrimental clinical effects (21). The rare sugars can be made by microbial and enzymatic reactions with ketose epimerase, aldose isomerase, aldose reductase, and oxidoreductase. Bioproduction strategies for all rare sugars have been illustrated with ring form structures (4).D-Psicose, a carbon-3 epimer of D-fructose, is present in small quantities in commercial carbohydrate or agricultural products. This rare sugar is absorbed poorly in the digestive tract (19), has zero energy for growth, is a useful sweetener used as an aid for weight reduction (18), represses hepatic lipogenic enzyme activity (16), and is nontoxic (17). Even though few studies have investigated the ability of D-tagatose 3-epimerase to convert D-fructose into D-psicose (7-9, 22), only one enzyme source, D-tagatose 3-epimerase from Pseudomonas cichorii, has been used for D-psicose production (8). The enzyme was purified and characterized (8), and the D-tagatose 3-epimerase gene was then cloned on the basis of the Nterminal amino acid sequence of the purified D-tagatose 3-epimerase. The gene was expressed in Escherichia coli and then characterized (7).In this study, the noncharacterized gene previously proposed as the D-tagatose 3-epimerase gene from Agrobacterium tumefaciens was cloned and expressed in E. coli. Biochemical properties such as metal ions, pH, temperature, epimerization reactions, and kinetic parameters were investigated. Determination of the equilibrium ratio and bioconversion between D-fructose and D-psicose by the D-psic...

Both the proponents and critics of Asian economic organization have been preoccupied with the ideal-typical management models of family businesses, and have rarely identified their changing management structures. We, instead, identify the change and continuity in these management structures through an analysis of family-controlled business groups in Singapore and South Korea before and after the Asian currency crisis. In our view, these business groups professionalized their management, but retained family control and corporate rule before the crisis. The crisis, however, increased the pressure on such groups to relinquish family control and corporate rule. Singaporean Chinese business groups tended to loosen their tight grip on corporate rule by absorbing more professional managers into their upper echelons. The surviving Korean chaebol, however, intensified family control. Only a few chaebol, which were on the brink of bankruptcy, relinquished corporate rule to professional managers. We argue that other than the market, cultural, and institutional factors as suggested in the existing literature, state capacities and strategies do matter in shaping the changing management structures of business groups. Drawing on our analysis, researchers will be able to conduct comparative studies of family businesses across East Asian societies, of organizational imitation, and of the role of the state in influencing management models.

This paper explores a natural generalization of the classic tandem-queue model, designed specifically to represent make- to-stock production processes. In such systems, intermediate and finished goods can be produced and stored in advance of demand. We consider the simplest version of the model, where demand is a Poisson process, and the unit production times are exponentially distributed. We propose and test a tractable approximation scheme. The approximation appears to be quite accurate.