Post-translational inhibitory regulation of acid invertase induced by fructose and glucose in developing apple fruit

Acid invertase (EC 3.2.1.26) is one of the key enzymes involved in the carbohydrate sink-organ development and the sink strength modulation in crops. The experiment conducted with 'Starkrimson' apple (Malus domestica Borkh) fruit showed that, during the fruit development, the activity of acid invertase gradually declined concomitantly with the progressive accumulation of fructose, glucose and sucrose, while Western blotting assay of acid invertase detected a 30 ku peptide of which the immuno-signal intensity increased during the fruit development. The im-muno-localization via immunogold electron microscopy showed that, on the one hand, acid invertase was mainly located on the flesh cell wall with numbers of the immunosignals present in the vacuole at the late stage of fruit development; and on the other hand, the amount of acid invertase increased during fruit development, which was consistent with the results of Western blotting. The in vivo pre-incubation of fruit discs with soluble sugars showed that     

Post-translational inhibitory regulation of acid invertase induced by fructose and glucose in developing apple fruit

Acid invertase (EC 3.2.1.26) is one of the key enzymes involved in the carbohydrate sinkorgan development and the sink strength modulation in crops. The experiment conducted with ‘Starkrimson’ apple (Malus domestica Borkh) fruit showed that, during the fruit development, the activity of acid invertase gradually declined concomitantly with the progressive accumulation of fructose, glucose and sucrose, while Western blotting assay of acid invertase detected a 30 ku peptide of which the immuno-signal intensity increased during the fruit development. The immunolocalization via immunogold electron microscopy showed that, on the one hand, acid invertase was mainly located on the flesh cell wall with numbers of the immunosignals present in the vacuole at the late stage of fruit development; and on the other hand, the amount of acid invertase increased during fruit development, which was consistent with the results of Western blotting. The in vivo preincubation of fruit discs with soluble sugars showed that the activity of extractible acid invertase was inhibited by fructose or glucose, while Western blotting did not detect any changes in apparent quantity of the enzyme nor other peptides than 30 ku one. So it is considered that fructose and glucose induced the post-translational or translocational inhibitory regulation of acid invertase in developing apple fruit. The mechanism of the post-translational inhibition was shown different from both the two previously reported ones that proposed either the inhibition by hexose products in the in vitro chemical reaction equilibrium system or the inhibition by the proteinaceous inhibitors. It was hypothesized that fructose and glucose might induce acid invertase inhibition by modulating the expression of some inhibition-related genes or some structural modification of acid invertase.     

Sorbitol and other carbohydrates in dormant apple shoots as influenced by controlled temperatures

The influence of controlled temperatures on levels of sorbitol and other carbohydrates was determined to provide further information on dormancy of apple trees (Malus sylvestris Mill.). For 3 years, 2-year-old “Red Delicious” apple shoots were collected from mature trees in an orchard at intervals during the autumn and winter, and shoots were stored for 6 hr to 1 week at temperatures from 18 to ?60 °C. Sorbitol and other carbohydrates were estimated in the sap or wood by gas chromatography.Controlled temperatures had a marked influence on the carbohydrate content of excised 2-year-old apple shoots. Levels of sorbitol in the sap were maximum at ?0.6 °C. The increase was greatest at the earliest sampling before complete hardening had occurred in each of the 3 years tested. Total sorbitol in the wood was less influenced by storage at various controlled temperatures than sorbitol in the sap. Levels of fructose, glucose, and sucrose in the wood were higher at temperatures below ?0.6 °C than at warmer temperatures. Levels of starch were usually inversely related to soluble sugars.     

Effect of Carbohydrate Demand on the Remobilization of Starch in Stolons and Roots of White Clover (Trifolium repens L.) after Defoliation

White clover plants were grown from stolon tips in growth cabinetsand then defoliated. Thereafter, changes in the contents ofnon-structural carbohydrates such as starch, sucrose, glucose,fructose, maltose, and pinitol in stolons and roots were monitored.Initial contents of carbohydrate reserves, photosynthetic supplyof new carbohydrates and carbohydrate demand after defoliationwere varied by growing the plants at various CO₂ partial pressures,by varying the extent of defoliation and by removing eitherroots or stolon tips at the time of defoliation. Remobilization of carbohydrate reserves in stolons increasedproportionally to their initial contents and was greater whenplants had been severely defoliated, suggesting that carbohydrateswere remobilized according to availability and demand. Starchwas the predominant reserve carbohydrate. Starch degradationwas associated with decreased contents of sucrose, glucose andfructose in young stolon parts and roots but not in old stolonparts suggesting that starch degradation was not strictly controlledby the contents of these sugars. A decrease in the demand forcarbohydrates by removal of roots did not decrease starch degradationbut increased the contents of sucrose, glucose, and fructose.Removal of stolon tips decreased starch degradation and contentsof sucrose, glucose, and fructose. The results suggest thatstarch degradation was controlled by a factor other than sucrose,glucose, and fructose which was exported from stolon tips, e.g.gibberellin. Key words: White clover, storage carbohydrates, remobilization, regrowth     

Role of carbohydrates in micropropagation of cork oak

The influences of carbon sources, fructose, glucose, sorbitol and sucrose on shoot proliferation and in vitro rooting of cork oak (Quercus suber L.) were compared at a wide range of concentrations (1–6%, w/v). The highest number of shoots occurred on glucose-containing medium. Nevertheless, we have chosen 3% sucrose which induced a similar rate of proliferation but favoured shoot elongation, permitting an effectively higher number of shoots during transfers. Sorbitol and autoclaved fructose did not stimulate shoot proliferation. Adventitious root formation was strongly dependent on carbohydrate supply. Sorbitol and autoclaved fructose were completely ineffectively on rooting induction. Glucose was the most effective carbon source on rooting promotion followed by sucrose and filter-sterilized fructose. The rooting response induced by fructose was dependent on the sterilizing procedure. The number of adventitious roots produced per shoot increased with increasing glucose and sucrose concentration. The content of reducing sugars in leaves of proliferation cultures and in leaves and roots of rooted plantlets was more dependent on carbon concentration than on glucose or sucrose supplement. The results presented here show that carbohydrate requirements during cork oak micropropagation depend upon the phase of culture. Sucrose (3%) and glucose (4%) were the best carbon sources respectively during proliferation and rooting phases.     

Feeding responses by female Pieris brassicae butterflies to carbohydrates and amino acids

Most Lepidoptera feed during the adult stage on carbohydrate‐rich food sources, primarily floral nectar. However, little is known about the factors leading to the acceptance of a possible food source. It is reported that butterflies select for nectar rich in sucrose and amino acids. This suggests that the insects have developed a sensitivity to these nectar compounds. We tested females of the large cabbage white, Pieris brassicae L. (Lepidoptera: Pieridae) for their responses to 10 different nectar‐ or honeydew‐sugars after either tarsal or proboscis stimulation. In no‐choice experiments, food‐deprived P. brassicae showed the strongest response to sucrose, followed by fructose. Other sugars, including galactose, glucose, maltose, mannose, melezitose, melibiose, raffinose and trehalose, did not elicit a feeding response. Mixtures of essential or common non‐essential amino acids did not stimulate feeding. In a choice situation, P. brassicae preferred sucrose over fructose, whereas they accepted a sucrose and amino acid solution equally to a plain sucrose solution. The results indicate that for P. brassicae, feeding is mainly elicited by sucrose and fructose.     

Reduced intake of carbohydrate prevents the development of obesity and impaired glucose metabolism in ghrelin O-acyltransferase knockout mice

A close relationship between acylated-ghrelin and sucrose intake has been reported. However, little has been examined about the physiological action of ghrelin on preference for different types of carbohydrate such as glucose, fructose, and starch. The current study was aimed to investigate the role of acylated-ghrelin in the determinants of the choice of carbohydrates, and pathogenesis of chronic disorders, including obesity and insulin resistance. In a two-bottle-drinking test, ghrelin O-acyltransferase (GOAT) knockout (KO) mice consumed a less amount of glucose and maltodextrin, and almost the same amount of fructose and saccharin solution compared to WT littermates. The increased consumption of glucose and maltodextrin was observed when acylated-ghrelin, but not unacylated-ghrelin, was exogeneously administered in normal C57BL/6J mice, suggesting an association of acylated-ghrelin with glucose-containing carbohydrate intake. When fed a diet rich in maltodextrin, starch and fat for 12 weeks, GOAT KO mice showed less food intake and weight gain, as well as improved glucose tolerance and insulin sensitivity than WT mice. Our data suggests that blockade of GOAT activity may offer a therapeutic option for treatment of obesity and its associated metabolic syndrome by preventing from overconsumption of carbohydrate-rich food.     

Dietary fiber and the glycemic response

Addition of purified fiber to carbohydrate test meals has been shown to flatten the glycemic response in both normal and diabetic volunteers, reduce the insulin requirement in patients on the artificial pancreas and in the longer term reduce urinary glucose loss and improve diabetes control. In the context of high fiber-high carbohydrate diets these findings have had a major impact in influencing recommendations for the dietary management of diabetes internationally. The mechanism of action appears in part to be due to the effect of fiber in slowing absorption rather than by increasing colonic losses of carbohydrate. Consequently postprandial GIP and insulin levels are reduced and the more viscous purified fibers (e.g., guar and pectin) appear most effective. In addition it has been suggested that colonic fermentation products of fiber may enhance glucose utilization. More recently it has become clear that many aspects of carbohydrate foods (food form, antinutrients, etc.) in addition to fiber may influence the rate of digestion and has led to a classification especially of starchy foods in terms of glycemic index to define the degree to which equicarbohydrate portions of different foods raise the blood glucose. Use of such data may maximize the effectiveness of high carbohydrate and high fiber diets in the management of diabetes and related disorders.     

罗汉果果肉中糖类物质组成与含量分析

罗汉果果实中富含糖分,糖类物质的组成及其含量对果实的内在品质有重要影响,然而多年来对其品质的研究多集中在罗汉果苷上,果实中可溶性糖种类与含量迄今尚未见有系统地报道。该研究以干燥的罗汉果果实为材料,采用PMP柱前衍生化一高效液相色谱紫外检测法、高效液相色谱示差折光检测法分别检测果肉中可溶性糖的种类与含量,并进行方法学考察。结果表明:PMP柱前衍生化一高效液相色谱紫外检测法只能检出罗汉果果实中存在的2种还原性醛糖——葡萄糖、甘露糖;而高效液相色谱示差折光检测法则可一次性检出葡萄糖、果糖、蔗糖、棉籽糖、多糖5种糖分。与柱前衍生化法相比,高效液相色谱示差折光检测法更适合用来全面分析罗汉果果实中糖分的种类和含量。不同罗汉果品种果实中糖的组分一致,但含量有显著差别。另外,样品的干燥方式会影响果实中的总糖及各组分的相对含量。冻干果肉中蔗糖和葡萄糖相对含量最高,烘干则导致蔗糖和葡萄糖下降,果糖与多糖相对含量增加。     

Relationship between ripening time and sugar content of apricot (<Emphasis Type="Italic">Prunus armeniaca</Emphasis> L.) kernels

Apricot seeds could be obtained as a byproduct in different juice or conserve producing industries. Disposal of large amount of apricot seeds is wasting of potentially precious sources of phytochemicals. This study encompassed apricot cultivars that have different origin and flowering time with the aim of providing valuable information about the sugar content in its kernels. High-performance anion-exchange chromatography with pulsed amperometric detection was used for the determination of 22 sugars in the kernels of 70 apricot cultivars. The most common sugars in the apricot kernels are sucrose, fructose, and glucose whose ratio proved to be ripening time dependent (1:1:1 in the early, 1:2:3 in medium and 1:3:3 in the late cultivars). The kernels of the apricot with shorter vegetation period had the highest sum of glucose and fructose compared to other groups. Other sugar components were present in different levels as minor constituents depending on the ripening time. Also, most common sugars and some low-level sugars were strongly correlated to each other, indicating the normal metabolic carbohydrate pathway. To understand the distribution modes of sugars, a principal component analysis was performed.     

Role of Competition for Sugars by Yeasts in the Biocontrol of Gray Mold of Apple

The yeasts, Cryptococcus laurentii BSR-Y22 or Sporobolomyces roseus FS-43-238, but not Saccharomyces cerevisiae BY-1, reduced gray mold ( Botrytis cinerea ) when applied to wounds of apples (cv. Golden Delicious) which were stored at 22IC for 7 days or 3IC for up to 2 months. The role of competition for sugars by these yeasts as a mechanism of antagonism was investigated at 22IC. Populations of C. laurentii and S. roseus in wounds were 6-9 times greater than those of S. cerevisiae from 1 to 7 days following inoculation. Yeasts in wounds utilized more 14C-labelled fructose, glucose or sucrose than conidia of B. cinerea during 48 h, but yeasts did not differ in their utilization of sugars. Utilization of 14C-sugars by yeasts in vitro was greater at most sampling times for conidia; the uptake after 48 h was always greater for yeasts and the addition of nitrogen did not alter this result. The utilization of 14C-sugars by S. roseus in vitro was greater than that in the other yeasts. The uptake and utilization of 14C-fructose by C. laurentii or S. roseus was greater than that of S. cerevisiae , but the utilization of glucose or sucrose by C. laurentii and S. cerevisiae was similar and the uptake of these sugars by these yeasts did not differ. Yeasts mixed with conidia in sterile, dilute solutions of fructose, glucose or sucrose, or in dilute apple juice inhibited conidial germination compared with no-yeast controls; S. cerevisiae was less effective than C. laurentii or S. roseus . Only yeasts rapidly depleted sugars from juice or sugar solutions. Yeasts did not alter the pH or oxygen content of dilute juice to the detriment of conidial germination. These results strongly suggest that competition for sugars by yeasts played a role in the biocontrol of gray mold, but that some other factor(s) most likely contributed to differences in efficacy between the yeasts.     

The role of sucrose during maturation of black spruce (Picea mariana) and white spruce (Picea glauca) somatic embryos

The present study was conducted to understand the role of sucrose in the medium on the maturation of black spruce and white spruce somatic embryos. A maturation medium containing 6% sucrose, which hydrolyzed into glucose and fructose, gave significantly more embryos than a medium containing 3.16% of each glucose and fructose. Preventing the complete sucrose hydrolysis by a daily transfer of the tissues onto fresh medium significantly decreased the yield of somatic embryos compared to when sucrose was allowed to complete its hydrolysis. This reduction was not due to the manipulation of the tissues during the transfer, since a daily in situ transfer did not affect embryo production. To verify if the better embryo production observed on a medium containing 6% sucrose was due to the increasing osmotic pressure of the medium, this increasing osmotic pressure was simulated with a sequence of media containing different concentrations of glucose and fructose. Unexpectedly and for both species, this simulation did not improve somatic embryo production, which stayed similar to the one obtained on constant osmotic pressure. To understand these results, embryos produced on the different treatments were analyzed in terms of sucrose, glucose, fructose and starch levels and protein contents. The embryo carbohydrate content was independent from the carbohydrate used in the maturation medium. However, embryos matured on 6% sucrose allowed to hydrolyze during the maturation period contained significantly more soluble and insoluble proteins than embryos matured on any other treatment. Furthermore, embryos with a higher protein content also exhibited a higher epicotyl appearance frequency. The role of sucrose as a regulatory factor during the maturation of spruce somatic embryos is discussed.     

Fructose and uric acid as drivers of a hyperactive foraging response: A clue to behavioral disorders associated with impulsivity or mania?

Several behavioral disorders, including attention deficit hyperactivity disorder (ADHD), bipolar disorder, and aggressive behaviors are linked with sugar intake and obesity. The reason(s) for this association has been unclear. Here we present a hypothesis supporting a role for fructose, a component of sugar and high fructose corn syrup (HFCS), and uric acid (a fructose metabolite), in increasing the risk for these behavioral disorders. Recent studies have shown that the reason fructose intake is strongly associated with development of metabolic syndrome is that fructose intake activates an evolutionary-based survival pathway that stimulates foraging behavior and the storage of energy as fat. While modest intake may aid animals that would like to store fat as a protective response from food shortage or starvation, we propose that high intake of sugar and HFCS causes a hyperactive foraging response that stimulates craving, impulsivity, risk taking and aggression that increases the risk for ADHD, bipolar disease and aggressive behavior. High glycemic carbohydrates and salty foods may also contribute as they can be converted to fructose in the body. Some studies suggest uric acid produced during fructose metabolism may mediate some of these effects. Chronic stimulation of the pathway could lead to desensitization of hedonic responses and induce depression. In conclusion, a hyperactive foraging response driven by high glycemic carbohydrates and sugars may contribute to affective disorders.     

Transport of fructose by a proton symport in a brewing yeast

Abstract Saccharomyces cerevisiae IGC4261, a brewing strain, transported fructose and sorbose but not glucose by a high-affinity, low-capacity proton symport. The symport was not subject to glucose repression and coexisted with the facilitated diffusion system for glucose, fructose, sorbose and other sugars. Transport by the symport was accumulative. The stoichiometry was one proton per molecule of fructose. Maltose acted as a non-competitive inhibitor.     

Carbohydrate status during somatic embryo maturation in Norway spruce

Summary The development of Norway spruce (Picea abies (L.) Karst.) somatic embryos on a maturation medium was accompanied by changes in nonstructural carbohydrate status. During embryo maturation, the content of total soluble sugars in the embryonal suspensor mass decreased and the partitioning between sucrose and hexoses changed considerably in favor of sucrose. Developing somatic embryos were mainly responsible for these changes. Osmotic stress caused by the presence of 3.75% polyethylene glycol (PEG) in the maturation medium (decrease in osmotic potential by 52.5 kPa) resulted in dramatic changes in the content of endogenous saccharides. There was a lower total carbohydrate content in the embryonal suspensor mass grown on the medium containing PEG in comparison with the untreated control. Isolated embryos from later stages of embryo development contained mainly sucrose with a small amount (20%) of fructose and nearly no glucose. A further increase in PEG concentration in the medium (7.5%; decrease in osmotic potential by 112.5 kPa compared to the maturation medium) led to a large increase in the total endogenous sugar content. This increase in sugars was a result of the enhanced content of sucrose, fructose, and glucose. The increased glucose content was in contrast to embryos grown on the medium with lower or no PEG content.     

The role of carbohydrates in the responses of chilling-sensitive plants to short- and long-term low-temperature treatments

The content of particular components of water-soluble carbohydrates and cold tolerance of cucumber (Cucumis sativus L.) cotyledonary leaves were studied at early developmental stages in dynamics during 6-day-long treatment with a temperature reduced to 12°C at two regimes: short-term cooling (2 h in the end of the night period, DROP) or permanent low-temperature treatment (PLT). PLT cucumber plants were characterized by the accumulation of oligosaccharides, whereas DROP plants contained increased amounts of glucose, fructose, and raffinose, indicating their higher metabolic status. When changes in carbohydrate fractions were compared with the dynamics of cold tolerance, it was found that these changes were synchronous in PLT plants but asynchronous for glucose and oligosaccharides in DROP plants. We suppose that, in cotyledonary leaves of DROP plants, two pools of sugars are produced; one of them used for tolerance development and another one — in active metabolism. This provides for the combination of activated metabolism and high cold tolerance of these plants. In PLT plants, all components of water-soluble carbohydrates are involved in cold tolerance development.     

Mutation of Clostridium thermocellum in the presence of certain carbon sources

Abstract When a cellobiose-grown inoculum of Clostridium thermocellum was transferred to either glucose or fructose as the sole carbon sourcem growth occurred only after a long lag of 180–200 h. We established that sugar uptake and phosphorylation were not limiting growth nor was the lag period the time take for a physiological adaptation process or for the growth of a mutant carried over in the cellibiose-grown incoculum. It became apparent that a mutation was occuring during the lag period in response to the selection pressure exerted by the presence of glucose or fructose as the sole carbon source. Once growth occurred on glucose and fructose, the cells could be transferred to cellobiose and back to glucose or fructose without exhibiting the long lag period. The change was stable over several transfers in the respective sugars.     

A comparison of nectar- and honeydew sugars with respect to their utilization by the hymenopteran parasitoid Cotesia glomerata

Fourteen naturally occurring sugars were individually tested with respect to their effect on Cotesia glomerata longevity. Parasitoids kept with solutions of either sucrose, glucose and fructose lived for >30 days. This constitutes a factor 15 increase in life span in comparison to control individuals kept with water only. Stachyose, mannose, melezitose, melibiose, maltose and erlose increased parasitoid longevity by a factor of 11.2-6.9. Solutions of galactose and trehalose had a marginal, but still significant effect. Lactose and raffinose did not raise parasitoid longevity, while rhamnose actually reduced parasitoid survival. In an additional experiment, the relationship between quantity of sugar consumption and longevity was established for all 14 sugars. To study the effect of an unsuitable sugar in sugar mixtures, a range of glucose:rhamnose mixtures was tested. Even at 20% of the sugar mixture rhamnose suppressed the nutritional benefit of the 80% glucose. The nutritional suitability of the sugars shows a positive correlation with the previously reported gustatory response towards the individual sugars. Patterns of sugar utilization are discussed with respect to hydrolytic enzymes and carbohydrate biochemical characteristics. Our findings for C. glomerata are compared to patterns of sugar utilization reported for other species. The comparison between C. glomerata and its host Pieris brassicae reveals that the parasitoid is capable of utilizing a range of sugars that are unsuitable to its herbivorous host. This specificity opens up opportunities to select food supplements for biological control programs that selectively target the antagonist, without concurrently enhancing herbivore fitness.     

Roles of cell-wall invertases and monosaccharide transporters in the growth and development of Arabidopsis

The hydrolysis of sucrose by cell-wall invertases (cwINV) and the subsequent import of hexoses into target cells appears to be crucial for appropriate metabolism, growth and differentiation in plants. Hexose uptake from the apoplast is catalysed by monosaccharide/H+ symporters (Sugar Transport Proteins or STPs), which have the potential to sense sugars. Import of extracellular hexoses may generate signals to orchestrate cellular activities, or simply feed metabolic pathways distinct from those fed by sucrose. It is predicted that Arabidopsis has six cwINV genes and at least 14 STP genes. These genes show different spatial and temporal patterns of expression, and several knock-out mutants have been isolated for analysis. AtSTP1 transports glucose, galactose, xylose, and mannose, but not fructose. It accounts for the majority of the AtSTP activity in vegetative tissues and its activity is markedly repressed by treatment with exogenous sugars. These observations are consistent with a role in the retrieval of cell-wall-derived sugars, for example, during carbohydrate limitation or cell expansion. The AtSTP1 gene is also expressed in developing seeds, where it might be responsible for the uptake of glucose derived from imported sucrose. The large number of AtcwINV and AtSTP genes, together with complex patterns of expression for each, and the possibility that each protein may have more than one physiological function, provides the plant with the potential for a multiplicity of patterns of monosaccharide utilization to direct growth and differentiation or to respond flexibly to changing environmental conditions.     

Inhibitory Effect of Carbohydrate on Flowering in Lemna perpusilla: II. Reversal by Glycine and l-Aspartate. Correlation with Reduced Levels of beta-Carotene and Chlorophyll

Flowering of Lemna perpusilla strain 6746 grown on 0.1 strength Hutner's medium in short days was inhibited by sucrose, glucose, fructose, and mannose, but not by various other sugars or metabolic intermediates. Only those sugars that inhibited flowering supported heterotrophic growth. Experiments with a single inductive long night indicated that an early stage in flowering was the sugar-sensitive process. Inhibition of flowering by carbohydrates was accompanied by reduced levels of chlorophyll and β-carotene. The inhibitory effects of carbohydrates on flowering were partially reversed by iminodiacetate, glycine, and l-aspartate but not by d-aspartate, ethylenediaminetetraacetate, acetate, δ-aminolevulinic acid, or mevalonic acid. The possibility is discussed that carbohydrate repression of flowering and of chloroplast pigments resulted from inadequate levels of amino acids.