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PubMed2006

Sugar and ABA response pathways and the control of gene expression.

Sugars are essential to plant growth and metabolism, both as energy source and as structural components. Sugar production and use are in part controlled at the level of gene expression by the sugars themselves. Responses to sugar are closely integrated with response pathways that indicate environmental conditions such as light and water availability. High sugar levels inhibit seedling development, repress photosynthetic gene expression and induce genes of storage metabolism such as those of starch biosynthesis. Genetic approaches have demonstrated the importance of abscisic acid (ABA) and the transcriptional regulator ABA-insensitive4 (ABI4) in sugar response pathways. Recent analysis of both photosynthetic and starch biosynthetic gene promoters suggest a direct role for ABI4 in their control. The increased understanding of the regulatory promoter elements controlling gene expression, in response to sugar and ABA, allows transcriptional networks to be understood at a molecular level.

Abscisic Acid↗

PubMed2005

Antisense oligodeoxynucleotide inhibition as a potent strategy in plant biology: identification of SUSIBA2 as a transcriptional activator in plant sugar signalling.

Sugar signalling cascades are important components of regulatory networks in cells. Compared with the situation in bacteria, yeast and animals, participants of the sugar signalling pathways in plants are poorly understood. Several genes involved in starch synthesis are known to be sugar inducible, although the signal transduction pathways remain undisclosed. We reported recently the isolation of SUSIBA2, a transcription factor involved in sugar-mediated regulation of starch synthesis. Here, we used antisense oligodeoxynucleotide (ODN) inhibition, a powerful approach in medical sciences, to block the effects of SUSIBA2 in sugar-treated barley leaves. The uptake and intracellular trafficking of an 18-mer susiba2 antisense ODN in leaves were followed by confocal microscopy. Administration of the antisense ODN to the leaves impeded susiba2 expression by RNase H activation. This dramatically diminished the ectopic expression of the iso1 and sbeIIb genes and resulted in altered starch synthesis. This study illustrates the successful exploitation of the antisense ODN technology in plant biology, e.g. as a rapid antecedent to time-consuming transgenic studies, and identifies SUSIBA2 as a transcriptional activator in plant sugar signalling. Based on our findings, we propose a model for sugar-signalling control of starch synthesis.

Gene Expression Regulation, Plant↗

PubMed1995

Site-directed mutagenesis and sugar-binding properties of the wheat germ agglutinin mutants Tyr73Phe and Phe116Tyr.

Wheat germ agglutinin is a dimeric lectin composed of two identical subunits. Each subunit consists of four homologous hevein-like domains of 42 or 43 amino acids each. Amino acid residues at the same position in each domain involved in sugar binding are thought to play a similar role in sugar binding. In order to clarify the role of the amino acid residue at domain position 30 of wheat germ agglutinin isolectin 2 (WGA2) in sugar binding, two WGA2 variants each containing a mutation, either Tyr73-->Phe (domain B) or Phe116-->Tyr (domain C), were produced. The binding activity for (GlcNAc)3 and the three-dimensional structure of these mutants were characterized by comparing with the properties of wild-type WGA2. Equilibrium dialysis experiments using (GlcNAc)3 indicated that the mutation Tyr73-->Phe reduced the overall sugar-binding activity at both pH 5.9 and pH 4.7. In addition, positive cooperativity toward (GlcNAc)3 binding was observed at pH 4.7. In contrast, the mutation of Phe116-->Tyr increased the overall sugar-binding activity at pH 5.9, but reduced this activity at pH 4.7 without changing the number of sugar-binding sites. Positive cooperativity was not observed at pH 5.9 or pH 4.7. X-ray crystallographic analysis of mutant WGA2 revealed that the mutation of Tyr73-->Phe caused a side chain movement of the Glu115 residue of the opposite subunit that formed a hydrogen bond with Tyr73 in wild-type WGA2. No changes were observed in the backbone structure and the disposition of the benzene ring of Phe73. The mutation Phe116-->Tyr caused the formation of a new hydrogen bond between Tyr116 and Glu72 of the opposite subunit. The changes in the sugar-binding properties in WGA2 mutants are discussed in relation to the structural change at the binding site.

Base Sequence↗

PubMed2005

The vinification of partially dried grapes: a comparative fermentation study of Saccharomyces cerevisiae strains under high sugar stress.

AIMS: The study of the fermentation performance of Saccharomyces cerevisiae strains under high sugar stress during the vinification of partially dried grapes. METHODS AND RESULTS: Microvinification of partially dried grape must with sugar concentration of 35 degrees Brix was performed using four commercial strains to carry out alcoholic fermentation. A traditional red vinification without nutrients addition was applied. Yeasts displayed different efficiency to convert sugar in ethanol and varied in glycerol yield. Sugar consumption and ethanol level were attested at 80-87% and 143.5-158.0 g l(-1) respectively. High correlation between sugar and assimilable nitrogen consumption rate was observed. Statistical treatment of data by principal component analysis highlighted the different behaviours that strains exhibited in regard to the production of higher alcohols and other compounds important to wine quality. CONCLUSIONS: Saccharomyces cerevisiae strains displayed appreciable capability to overcome osmotic stress and to yield ethanol fermenting high sugar concentration grape must in winemaking condition. SIGNIFICANCE AND IMPACT OF THE STUDY: The results provided insights on the strain contribution to wine quality subordinate to stress condition. This investigation is of applicative interest for winemaking and processing industry that use high sugar concentration musts.

Carbohydrate Metabolism↗

PubMed1990

Patterns of sugar consumption in early childhood.

Patterns of sugar consumption were studied prospectively in a birth cohort of 231 Norwegian children. Information on dietary habits and sugar consumption was collected at the children's ages of 10 months, 18 months, and 2 yr. The results of the factor analyses showed that the children's sugar consumption constituted a separate dimension of dietary habits. Patterns of sugar consumption seemed to be established already during infancy. The children's sugar consumption increased from infancy to the age of 2 yr, and the patterns of sugar consumption also seemed to be maintained throughout the first years of early childhood. Sugar consumption was also analyzed multivariately using indicators of social background and family size as explanatory variables, but the explanatory power of these variables was rather poor and decreasing with age.

Analysis of Variance↗

PubMed2004

Temporal stability of the theory of planned behavior: a prospective analysis of sugar consumption among Ugandan adolescents.

PURPOSE: This study addressed three questions: What is the power of the Theory of Planned Behavior (TPB) in predicting adolescents' intended and self-perceived consumption of non-milk extrinsic sugars using a non-intervention prospective approach? To what extent do the TPB constructs change across time following adolescents' mere exposure to an oral health survey? Do changes in self-perceived sugar consumption at follow-up associate with changes in behavioral intention as predicted by the TPB? METHOD: A survey was conducted in Kampala (urban) and Lira (rural) and 1146 secondary school students completed questionnaires assessing the TPB at school (Time 1). A random sub-sample of 415 students was selected from the original survey of which 372 students were examined clinically. After 3 months (Time 2), the questionnaire was administered a second time in the sub-sample. All analyses are based on the number of students who participated on both survey occasions, n = 372. RESULTS: Attitudes and perceived behavioral control predicted intended sugar consumption at Time 1 and Time 2, accounting for 58% (DeltaR(2) = 0.58) and 19% (DeltaR(2) = 0.19) of the variance, respectively. Time 1 intention provided significant prediction of Time 2 self-perceived sugar consumption with DeltaR(2) = 0.5. Adolescents with high-caries experience more than their counterparts with low, changed towards weaker intentions and less frequent sugar consumption across the survey period. Mean sugar consumption scores changed from 2.6 to 2.7 (ns), 3.1 to 2.6 (P < 0.001) and 2.3 to 3.2 (P < 0.001) among adolescents who, respectively, remained stable, increased and decreased their intentions across time. CONCLUSION: This study supports the validity of the TPB in predicting intended and self-perceived sugar consumption prospectively.

Adolescent↗

PubMed1979

Effects of a sugar mixture on blood alcohol parameters and impairment in the intact rat.

The effects of a sugar mixture containing 43% glucose and 36% fructose on ethanol metabolism and on ethanol-induced impairment were studied in intact rats. When ethanol was given orally mixed with the sugars there was a significant reduction in the area of the blood alcohol time curve accompanied by a decrease in the peak ethanol concentration and a slowing in the rate of ethanol absorption. The whole curve followed a lower course and the time for complete removal of ethanol from the body was markedly reduced even though the slope of the elimination phase (beta) was not significantly increased. Ethanol-induced impairment as measured using a tilting plane device was significantly less when ethanol was given mixed with the sugars and paralleled the reduced area and duration of the blood alcohol curve. The magnitude of the effect observed on blood alcohol levels and impairment was dependent on the dose of sugars administered in relation to the alcohol dose. When the sugars were given orally after absorption and distribution of ethanol were complete the slope of the elimination phase (beta) was increase by 30%. These findings point to an increased rate of ethanol metabolism in rats in the presence of sugars. The action of the sugars prevails only for the first few hours after administration thereafter the rate of ethanol metabolism returns to normal.

Administration, Oral↗

PubMed1983

Characterization of sugar transport in the pigeon red blood cell.

Sugar transport in pigeon red blood cells is mediated by two pathways. One is saturable, shows competition between sugars, is inhibited by phloretin and cytochalasin B, and shows many of the properties of 'carrier-mediated' transport, characterized in the human red blood cell. The other is not saturable, and shows no competition between sugars. The saturable pathway is virtually absent from freshly drawn cells, but may be stimulated by pre-incubation with 2 mM-NaCN, or by Ca and the ionophore A 23187. The non-saturating pathway is stimulated only slightly by CN, but considerably by Ca and A 23187. The inhibition of sugar transport by cytochalasin B is antagonized competitively by sugars acting at the inner surface of the membrane. External sugars have no effect, as in the human red blood cell (Widdas, 1980). The binding of cytochalasin B to the cells shows a limited number of high-affinity sites. These are unrelated to inhibition of sugar transport as binding, but not transport, is prevented by the presence of cytochalasin E.

3-O-Methylglucose↗

PubMed1989

Growth of Neocallimastix sp. Strain R1 on Italian Ryegrass Hay: Removal of Neutral Sugars from Plant Cell Walls.

The anaerobic fungus Neocallimastix sp. strain R1 was grown for up to 5 days on a medium containing autoclaved Italian ryegrass hay as the carbon source. Culture supernatants and digested cell walls were harvested at 12-h intervals. Supernatants were analyzed for the fermentation products formate and acetate, and residual cell walls were analyzed for dry-matter and neutral-sugar losses. Fungal growth was accompanied by the digestion of plant cell walls and the accumulation of fermentation products in culture media. Dry-matter losses were accounted for by removal of four major neutral sugars (arabinose, galactose, glucose, and xylose) from the plant cell walls. First-order reaction kinetics could be used to describe the loss of each sugar. All cell wall sugars, including arabinose and galactose, which are not fermented by Neocallimastix sp. strain R1 were removed simultaneously. Although the rates of removal of individual sugars were similar, there were significant differences in their extents of removal: the extent of removal of arabinose exceeded that of the other three sugars, and xylose was the least digestible. This study provides the first account of simultaneous (nonpreferential) removal of neutral sugars from plant cell walls by an anaerobic fungus. Although in vitro techniques were used, these results indicate a potentially significant role for the anaerobic fungi as fiber digesters in the rumen.

Journal Article↗

PubMed1977

Pyruvate formation during the catabolism of simple hexose sugars by Escherichia coli: studies with pyruvate kinase-negative mutants.

Escherichia coli K-12 mutants lacking the adenosine 5'-monophosphate-activated pyruvate kinase have been isolated accidentally and used to prepare further mutants additionally devoid of the fructose bisphosphate-activated pyruvate kinase. Such double mutants totally devoid of pyruvate kinase activity still grow well under aerobic conditions on sugars that are catabolized by the phosphoenolpyruvate (PEP):sugar phosphotransferase system, but they grow poorly on non-phosphotransferase system sugars. This suggests that although pyruvate kinase plays a major role in the formation of pyruvate from PEP during growth on non-phosphotransferase system sugars, the operation of the PEP:sugar phosphotransferase system can contribute significantly to pyruvate production from PEP. In the absence of pyruvate kinase and an active PEP:sugar phosphotransferase system the methylglyoxal glycolytic bypass may also function to some extent for the formation of pyruvate during the catabolism of simple hexose sugars. No unique physiological role can yet be ascribed to the adenosine 5'-monophosphate-activated pyruvate kinase as a result of these studies.

Escherichia coli↗

PubMed1987

Amino sugars in the glycoprotein toxin from Bacillus thuringiensis subsp. israelensis.

The carbohydrate content of purified Bacillus thuriniensis subsp. israelensis crystal toxin was determined by six biochemical tests, column chromatography on an amino acid analyzer, and the binding of 11 fluorescent lectins. The crystals contained approximately 1.0% neutral sugars and 1.7% amino sugars. The amino sugars consisted of 70% glucosamine and 30% galactosamine. No N-acetylneuraminic acid (sialic acid) was detected. The presence of amino sugars was confirmed by the strong binding of fluorescent wheat germ agglutinin and the weak binding of fluorescent soybean agglutinin. These lectins recognize N-acetyl-D-glucosamine and N-acetyl-D-galactosamine, respectively. The lectin-binding sites appeared evenly distributed among the protein subunits of the crystal. The sugars were covalently attached to the crystal toxin because wheat germ agglutinin still bound alkali-solubilized toxin which had been boiled in sodium dodecyl sulfate, separate by polyacrylamide gel electrophoresis, and transferred to nitrocellulose membranes. This study demonstrates the covalent attachment of amino sugars and indicates that the B. thuringiensis subsp. israelensis protein toxins should be viewed as glycoprotein toxins. The crystals used in the present study were purified on sodium bromide density gradients. Studies employing crystals purified on Renografin density gradients can give artificially high values for the anthrone test for neutral sugars.

Bacillus thuringiensis↗

PubMed1962

Survival of Serratia marcescens after freeze-drying or aerosolization at unfavorable humidity. I. Effects of sugars.

Zimmerman, Leonard (U.S. Army Biological Laboratories, Fort Detrick, Frederick, Md.). Survival of Serratia marcescens after freeze-drying or aerosolization at unfavorable humidity. I. Effects of sugars. J. Bacteriol. 84:1297-1302. 1962.-Suspensions of Serratia marcescens were subjected to freeze-drying or to aerosolization at unfavorable humidity levels. The survival of the cells during one or the other of these treatments was markedly improved in the presence of common sugars, but no one sugar stabilized the cells against both stresses. The protective effects of the sugars were correlated with their penetrability into cells; minimally penetrable sugars stabilized cells against aerosolization, and freely penetrable sugars stabilized cells during freeze-drying. These results were attributed to the modifications of intracellular water content induced by the presence of the sugars in the cell suspensions.

Carbohydrates↗

PubMed2006

Sugar sensing and signaling in plants: conserved and novel mechanisms.

Sugars not only fuel cellular carbon and energy metabolism but also play pivotal roles as signaling molecules. The experimental amenability of yeast as a unicellular model system has enabled the discovery of multiple sugar sensors and signaling pathways. In plants, different sugar signals are generated by photosynthesis and carbon metabolism in source and sink tissues to modulate growth, development, and stress responses. Genetic analyses have revealed extensive interactions between sugar and plant hormone signaling, and a central role for hexokinase (HXK) as a conserved glucose sensor. Diverse sugar signals activate multiple HXK-dependent and HXK-independent pathways and use different molecular mechanisms to control transcription, translation, protein stability and enzymatic activity. Important and complex roles for Snf1-related kinases (SnRKs), extracellular sugar sensors, and trehalose metabolism in plant sugar signaling are now also emerging.

Biosensing Techniques↗

PubMed1995

Mosquito sugar feeding and reproductive energetics.

Sugar feeding is a fundamental characteristic of mosquito life. Most evidence indicates frequent ingestion by both sexes and all ages of mosquitoes of plant sugar, usually as floral and extrafloral nectar and honeydew. Energetically, sugar and blood are interchangeable; females of some species have evolved independence from one or the other, but most need blood to develop eggs and sugar to survive, to fly, and to enhance reproduction. Mosquitoes' commitment to sugar is further illustrated by a wealth of behavioral, structural, and physiological specializations for finding, feeding on, and processing it. Blood and sugar feeding activities are antagonistic and mutually exclusive, owing to conflicting demands, yet they support the same goals and often share the same activity period. The rules by which females make food-choice decisions have been inadequately explored, and we still lack convincing evidence that sugar availability in nature varies sufficiently to affect mosquito populations.

Animals↗

PubMed1985

Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport.

Zero-trans kinetics of Na+-sugar cotransport were investigated. Sugar influx was measured at various sodium and sugar concentrations in K+-loaded cells treated with rotenone and valinomycin. Sugar influx follows Michaelis-Menten kinetics as a function of sugar concentration but not as a function of Na+ concentration. Nine models with 1:1 or 2:1 sodium:sugar stoichiometry were considered. The flux equations for these models were solved assuming steady-state distribution of carrier forms and that translocation across the membrane is rate limiting. Classical enzyme kinetic methods and a least-squares fit of flux equations to the experimental data were used to assess the fit of the different models. Four models can be discarded on this basis. Of the remaining models, we discard two on the basis of the trans sodium dependence and the coupling stoichiometry [G. A. Kimmich and J. Randles, Am. J. Physiol. 247 (Cell Physiol. 16): C74-C82, 1984]. The remaining models are terter ordered mechanisms with sodium debinding first at the trans side. If transfer across the membrane is rate limiting, the binding order can be determined to be sodium:sugar:sodium.

Animals↗

PubMed2003

Enhanced responses of the chorda tympani nerve to sugars in the ventromedial hypothalamic obese rat.

Sweet taste sensitivity in obese rats with lesions of the ventromedial hypothalamus (VMH) was studied by examining chorda tympani nerve responses to various taste stimuli including sugars. In the early progressive phase of obesity (2 wk after creating VMH lesions), there was no significant difference in the nerve responses to any taste stimulus between sham-operated and VMH-lesioned rats. In contrast, in the late phase of obesity (15-18 wk after VMH lesions), the magnitude of responses to sugars (except for fructose) was prominently greater than that in age-matched controls. High-fat diet-induced obese rats and streptozotocin-diabetic rats also showed greater chorda tympani nerve responses to sugars as was observed in VMH-lesioned obese rats, indicating that VMH lesions might not be specifically related to the enhanced gustatory neural responses to sugars. Although it has been demonstrated that the enhanced responses of the chorda tympani nerve to sugars in genetically diabetic db/db mice is largely attributable to the lack of the direct suppressive effect of leptin on the taste receptor cells, plasma leptin levels were not correlated with the changes in chorda tympani responsiveness to sugars in these models of obesity and diabetes. Accordingly, our results suggest that some chronic factors, including high blood glucose, inefficiency of insulin action, or leptin resistance may be related to the enhancement of chorda tympani nerve responses to sugars.

Animals↗

PubMedDate not supplied

Sugars - the arch criminal?

Numerous lines of evidence have conclusively established the role of sugars in caries etiology and the importance of sugars as the principal dietary substrate that drives the caries process has not been scientifically challenged. While sugars appear to differ little in acidogenic potential, sucrose has been given special importance, as the sole substrate for synthesis of extracellular glucans. Water-insoluble glucans might enhance accumulation of mutans streptococci on smooth tooth surfaces and appear to enhance virulence by increasing plaque porosity, resulting in greater acid production immediately adjacent to the tooth surface. Data indicating that the sugar consumption/caries relationship is now weaker have led to suggestions that recommendations to restrict sugar consumption are no longer necessary. Clearly, fluoride has raised the threshold of sugar intake at which caries will progress to cavitation, but fluoride has its limits, and caries remains a serious problem for disadvantaged individuals in many industrialized countries and is a rising problem in many developing countries. A weakening of the sugar/caries relationship may also be explained by many technical, biological, behavioral and genetic factors. Future research should aim to determine the biologic and behavioral factors that influence caries risk. Measures to educate the public on the dangers of frequent sugar consumption, combined with recommendations for proper oral hygiene and fluoride use, are still warranted. Individual dietary counseling is highly recommended for patients at high caries risk. As dental caries is a preventable disease, each country must decide: what level of disease is society willing and able to tolerate?

Dental Caries↗

PubMed1988

Geographic and temporal variations of sugar and margarine consumption in relation to Crohn's disease.

Patients with Crohn's disease show an increased consumption of refined sugar compared to controls. It was speculated that the frequent occurrence of Crohn's disease in developed countries might be related to a high intake of refined sugar. In contrast, others suggested margarine consumption to play a role in the etiology of Crohn's disease, the hypothesis being based on the seemingly simultaneous onset of margarine consumption and the first reports of granulomatous ileitis and the similarities in their geographic distribution. Both hypotheses, however, have not been subjected to a rigorous epidemiologic analysis. In the present study, the per capita consumption of refined sugar and margarine were correlated with the incidence and mortality of Crohn's disease from different countries. The time trends of mortality from Crohn's disease were compared to those of sugar and margarine intake. Two weak correlations were found between the geographic distribution of sugar and margarine consumption and mortality from Crohn's disease, the correlations resulting from the difference between two types of countries. Compared to Canada, the United States and most countries from Northern Europe on one side, Japan and most Mediterranean countries on the other side were characterized by low consumption of the two nutrients as well as low mortality from Crohn's disease. No consistent pattern was found, however, within each group of countries. No significant correlation was found between sugar or margarine consumption and the incidence of Crohn's disease. The time trends of Crohn's disease in different countries were not matched by similar time trends of either sugar or margarine consumption. The different epidemiologic behavior of the two nutrients and Crohn's disease indicates that variations in their dietary intake were not responsible for the geographic and temporal patterns of Crohn's disease. Other factors must be sought to explain the characteristic epidemiology of Crohn's disease.

Cohort Studies↗