Sensitivity of antennal gustatory receptor neurones to aphid honeydew sugars in the carabid Anchomenus dorsalis

Using electrophysiology, the stimulating effect of 13 sugars and three sugar alcohols (each at a concentration of 100 mm ) to antennal gustatory receptor neurones (GRNs) is tested in the carabid beetle Anchomenus dorsalis (Pontoppidan, 1763) (Coleoptera, Carabidae). Maltose, sucrose, glucose and raffinose are the most stimulating sugars for the sugar‐sensitive neurone (SuN), evoking 6.7–18.6 spikes s^?1 in fed insects, whereas the others had little or no effect. The firing rate of the antennal GRNs is not affected by any of the tested sugar alcohols, dulcitol, inositol and sorbitol. Additionally, concentration/response curves for sucrose and maltose are obtained in the range 0.01–100 mm . The responses of beetles starved for 96 h to this range of sucrose are two‐ to three‐fold higher compared with those of fed beetles. The presence of a terminal α‐glucose unit is an important feature of the molecular structure determining the stimulating properties of the two disaccharides, maltose and sucrose, as well as glucose. The other monosaccharide unit of the molecule is also of great importance in determining the stimulating properties of various disaccharides. The sensitivity of the SuN to the four most prevalent aphid honeydew sugars suggests that A. dorsalis uses these chemicals as sensory cues when searching for aphids as prey.     

std1, a Gene Involved in Glucose Transport in Schizosaccharomyces pombe

A wild-type strain, Sp972 h⁻, of Schizosaccharomyces pombe was mutagenized with ethylmethanesulfonate (EMS), and 2-deoxyglucose (2-DOG)-resistant mutants were isolated. Out of 300 independent 2-DOG-resistant mutants, 2 failed to grow on glucose and fructose (mutants 3/8 and 3/23); however, their hexokinase activity was normal. They have been characterized as defective in their sugar transport properties, and the mutations have been designated as std1-8 and std1-23 (sugar transport defective). The mutations are allelic and segregate as part of a single gene when the mutants carrying them are crossed to a wild-type strain. We confirmed the transport deficiency of these mutants by [¹⁴C]glucose uptake. They also fail to grow on other monosaccharides, such as fructose, mannose, and xylulose, as well as disaccharides, such as sucrose and maltose, unlike the wild-type strain. Lack of growth of the glucose transport-deficient mutants on maltose revealed the extracellular breakdown of maltose in S. pombe, unlike in Saccharomyces cerevisiae. Both of the mutants are unable to grow on low concentrations of glucose (10 to 20 mM), while one of them, 3/23, grows on high concentrations (50 to 100 mM) as if altered in its affinity for glucose. This mutant (3/23) shows a lag period of 12 to 18 h when grown on high concentrations of glucose. The lag disappears when the culture is transferred from the log phase of its growth on high concentrations. These mutants complement phenotypically similar sugar transport mutants (YGS4 and YGS5) reported earlier by Milbradt and Hoefer (Microbiology 140:2617–2623, 1994), and the clone complementing YGS4 and YGS5 was identified as the only glucose transporter in fission yeast having 12 transmembrane domains. These mutants also demonstrate two other defects: lack of induction and repression of shunt pathway enzymes and defective mating.     

Characteristics of Pseudomonas solanacearum

Summary: A collection of 185 isolates of Pseudomonas solanacearum has been classified into 4 biotypes according to their capacity to oxidize 3 disaccharides (lactose, maltose and cellobiose) and 3 hexose alcohols (mannitol, sorbitol and dulcitol). Biotype 2 which oxidized the disaccharides but not the hexose alcohols appears to have a restricted host range; it was obtained solely from two plant hosts, potato and tomato, whereas biotype 1, which oxidized neither group of carbohydrates, and biotype 3 which oxidized both, were obtained from a diversity of plant hosts. A bacteriophage isolated from material infected with biotype 2 showed a high degree of specificity for isolates of biotype 2. The present known distribution of the 4 biotypes is given and their relationship to host range is discussed. A neotype culture for Ps. solanacearum is proposed.     

Responses of the ant Lasius niger to various compounds perceived as sweet in humans: a structure-activity relationship study

A behavioural study on the ant Lasius niger was performed by observing its feeding responses to 85 compounds presented in a two-choice situation (tested compound versus water control or sucrose solution). Among these compounds, only 21 were phagostimulating: six monosaccharides (D-glucose, 6-deoxy-D-glucose, L-galactose, L-fucose, D-fructose, L-sorbose), four derivatives of D-glucose (methyl alpha-D-glucoside, D-gluconolactone and 6-chloro- and 6-fluoro-deoxy-D-glucose), five disaccharides (sucrose, maltose, palatinose, turanose and isomaltose), one polyol glycoside (maltitol), three trisaccharides (melezitose, raffinose and maltotriose) and two polyols (sorbitol and L-iditol). None of the 16 non-carbohydrate non-polyol compounds tested, although perceived as sweet in humans, was found to be active in ants. The molar order of effectiveness of the major naturally occuring compounds (melezitose > sucrose = raffinose > D-glucose > D-fructose = maltose = sorbitol) is basically different from the molar order of their sweetness potency in humans (sucrose > D-fructose > melezitose > maltose > D-glucose = raffinose = sorbitol). On a molar basis melezitose is in L. niger about twice as effective as sucrose or raffinose, while D-glucose and D-fructose are three and four times less effective, respectively, than sucrose or raffinose. From a structure-activity relationship study it was inferred that the active monosaccharides and polyols should interact with the ant receptor through only one type of receptor, through the same binding pocket and the same binding residues, via a six-point interaction. The high effectiveness of melezitose in L. niger mirrors the feeding habits of these ants, which attend homopterans and are heavy feeders on their honeydew, which is very rich in this carbohydrate.     

Stimulation of the labellar sugar receptor of the fleshfly by mono- and disaccharides

Responses of the labellar sugar receptor of the fleshfly, Boettcherisca peregrina, were studied over a wide range of concentrations of several sugars (sucrose, maltose, glucose, fructose, and mannose) in single solutions and in mixtures. The results suggest (a) that the receptor sites are not completely differentiated for glucose and for fructose combination, (b) that the receptor site is composed of two subunits. Such suggestions are based on the classical model, where the response is proportional to the number of the sites, two subunits of each site being simultaneously occupied with one molecule of disaccharides or two molecules of monosaccharides. It is shown, however, that an allosteric model gives a somewhat better interpretation of the experimental results.     

Studies on the permeability of rat liver lysosomes to carbohydrates

1. The latency of nitrocatechol sulphatase activity was measured in rat liver lysosomes before and after preincubation in 0.25m solutions of 25 different carbohydrates. 2. Preincubation in disaccharides, hexitols, gluconate, glucuronate or lactate gave little or no rise in ;free' sulphatase activity, indicating that these compounds do not easily penetrate the lysosomal membrane, but incubation in monosaccharides or the lower glycitols caused a progressive loss of latency. 3. Rates of increase in ;free' activity were taken as an indication of rates of solute penetration into lysosomes and were correlated with the structure and molecular weight of each sugar. 4. Additional evidence for non-penetration of maltose was obtained by demonstrating that the latency of lysosomal alpha-glucosidase is independent of substrate concentration employed. 5. The results are discussed in the light of published data on the latency of lysosomal enzymes.     

Gustatory perception and metabolic utilization of sugars by<Emphasis Type="Italic"> Myrmica rubra</Emphasis> ant workers

The suitability of various nectar and honeydew sugars as a food source for the polyphagous ant species M. rubra (L.) was studied. The sugars used included monosaccharides (fructose, glucose, galactose, mannose, rhamnose), disaccharides (sucrose, maltose, trehalose, melibiose, lactose) and trisaccharides (melizitose, raffinose, erlose). Single-sugar solutions were tested on ant workers in a long-term laboratory bioassay in which acceptance of the solutions and ant survival were recorded. The acceptance of the sugars was confirmed in a second bioassay in which feeding time was established. Enzymatic hydrolysis of sucrose, maltose and melibiose was investigated through HPLC analyses of workers fed these disaccharides. Sugar acceptance and feeding time were related to ant survival. Considering the monosaccharide units of which the sugars are composed, fructose seems especially suitable as a short-term energy source, while glucose appears to be used both directly and for storage. The presence of a galactose unit appears to reduce sugar suitability. It is suggested that the workers possess invertase and maltase and to a lesser degree also galactosidase. The gustatory perception is correlated with the profitability of sugars in further metabolic processes.     

Sucrose-enhanced biosynthesis of medicinally important antioxidant secondary metabolites in cell suspension cultures of <Emphasis Type="Italic">Artemisia absinthium</Emphasis> L.

Natural products are gaining tremendous importance in pharmaceutical industry and attention has been focused on the applications of in vitro technologies to enhance yield and productivity of such products. In this study, we investigated the accumulation of biomass and antioxidant secondary metabolites in response to different carbohydrate sources (sucrose, maltose, fructose and glucose) and sucrose concentrations (1, 3, 5, 7 and 9 %). Moreover, the effects of 3 % repeated sucrose feeding (day-12, -18 and -24) were also investigated. The results showed the superiority of disaccharides over monosaccharides for maximum biomass and secondary metabolites accumulation. Comparable profiles for maximum biomass were observed in response to sucrose and maltose and initial sucrose concentrations of 3 and 5 %. Maximum total phenolic and total flavonoid contents were displayed by cultures treated with sucrose and maltose; however, initial sucrose concentrations of 5 and 7 % were optimum for both classes of metabolites, respectively. Following 3 % extra sucrose feeding, cultures fed on day-24 (late-log phase) showed higher biomass, total phenolic and total flavonoid contents as compared to control cultures. Highest antioxidant activity was exhibited by maltose-treated cultures. Moreover, sucrose-treated cultures displayed positive correlation of antioxidant activity with total phenolics and total flavonoids production. This work describes the stimulatory role of disaccharides and sucrose feeding strategy for higher accumulation of phenolics and flavonoids, which could be potentially scaled up to bioreactor level for the bulk production of these metabolites in suspension cultures of A. absinthium.     

Sporulation in Hansenula wingei Is Induced by Nitrogen Starvation in Maltose-Containing Media

The sexually agglutinative yeast Hansenula wingei lives in association with bark beetles that inhabit coniferous trees. This yeast was induced to sporulate by malt extract, which contains a high percentage of maltose (50%) and a low percentage of nitrogen (0.5%). A solution of 1.5% maltose without any growth factors also induced ascosporogenesis in H. wingei. Thus, only a carbon source is required for sporulation as in Saccharomyces. However, potassium acetate did not induce sporulation in H. wingei as it does in S. cerevisiae. Instead, disaccharides (such as maltose, sucrose, or cellobiose) promote sporulation better than either monosaccharides (such as dextrose, fructose, or mannose) or respiratory substrates (such as ethanol or glycerol). The specificity of disaccharides in promoting sporulation in H. wingei may be considered an adaptation since these disaccharides are present in the natural environment of this yeast. In addition, the specificity of disaccharides may be related to the induction of the disaccharidase because cells precultured on dextrose sporulate well on maltose, but cells precultured on maltose sporulate poorly on maltose. When (NH₄)₂SO₄ was added at a low concentration (3 mM) to synthetic sporulation medium (1.5% maltose solution), sporulation was abolished, whereas other salts and nitrogen sources inhibited to a lesser extent and vitamins and trace elements had no effect. Oxygen was required for sporulation, as expected for an obligate aerobe. Maximal sporulation was achieved in 2% malt extract broth at high cell density (10⁹ cells per ml), pH 5, and 25°C. By using these optimal physiological conditions and hybrid strains selected from an extensive genetic breeding program, about 30% asci (10% tetrads) were obtained routinely. Thus, the genetics of cell recognition in this yeast can now be studied.     

The in vivo and in vitro substrate specificity of quinoprotein glucose dehydrogenase of Acinetobacter calcoaceticus LMD79.41

Quinoprotein glucose dehydrogenase (GDH; EC 1.1.99.17) was partially purified from cell-free extracts of Acinetobacter calcoaceticus LMD79.41. The enzyme oxidized monosaccharides (d-glucose, d-allose, 2-deoxy-d-glucose, d-galactose, d-mannose, d-xylose, d-ribose and l-arabinose) as well as disaccharides (d-lactose, d-maltose and d-cellobiose).Intact cells of A. calcoaceticus LMD79.41 also oxidized these monosaccharides, but not the disaccharides.The difference in substrate specificity can not be explained by impermeability of the outer membrane for disaccharides, since right-side-out membrane vesicles did not oxidize disaccharides either. Destruction of the cytoplasmic membrane strongly affected the catalytic properties of GDH. Not only did the affinity towards some monosaccharides change substantially, but disaccharides also became good substrates upon solubilization of the enzyme. Thus, at least in A. calcoaceticus LMD79.41, the oxidation of disaccharides by GDH can be considered as an in vitro ‘artefact’ caused by the removal of the enzyme from its natural environment.     

Sweetening agents of plant origin*

The most important sweet substance known is sucrose, which is obtained commercially from sugar cane and sugar beet. Because the intake of sucrose has been associated with a number of adverse effects on health, an intensive search has been undertaken to find alternative substances to satisfy the human craving for a sweet taste. Many other plant‐derived compounds are sweet, ranging in structural complexity from sugars and polyhydric alcohols through diterpene and triterpene glycosides to proteins; some of these compounds are intensely sweet, being hundreds or even thousand times sweeter than sucrose, and offer potential for commercial use in dietetic and diabetic foodstuffs. The present review examines the role of ethnobotany in the discovery of sweet‐tasting plants, the chemical isolation and elucidation of the sweet compounds, and some safety and sensory evaluation aspects of these compounds. A discussion on the future prospects of discovering and developing new plant‐derived sweeteners concludes the review.     

Physiological and biochemical characteristics of fast-and slow-growing Rhizobium sp. pigeonpea (Cajanus cajan)

Thirty-two of 38 cultures isolated from the nodules of pigeonpea plants were rapid growers. The generation time of rapid growers varied from 0·71 to 1·31 h and slow growers from 7·7 to 9·9 h. Rapid growers oxidized pentoses, hexoses, polyhydric alcohols (except dulcitol), tricarboxylic acid cycle intermediates (except citrate) and disaccharides more rapidly than slow growers; disaccharides were not oxidized by any of the slow growers. The Embden-Meyerhof-Parnas and Entner-Doudoroff pathways and the tricarboxylic acid cycle were present in both rapid and slow growers, whereas the pentose-phosphate pathway was present only in rapid growers.     

Micropropagation of socotran fig, <Emphasis Type="Italic">Dorstenia gigas</Emphasis> schweinf. Ex Balf. F. —A threatened species,endemic to the island of Socotra,Yemen

Summary As an alternative to seed propagation, and efficient micropropagation system based on axillary shoot formation and subsequent rooting was developed for the threatened and medicinal plant species Dorstenia gigas (Moraceae). Three different basal media were tested. For the best basal medium, a modified WPM medium, different concentrations of the carbohydrates sucrose, glucose, fructose and maltose were tested. The total number of shoots was not markedly affected. For all carbohydrates but maltose, however, there was a reduction in the number of normal, healthy shoots for carbohydrate concentrations greater than 14.6 mM for the disaccharides and 27.8 mM for the monosaccharides (i.e., approximately 5 gl⁻¹). Using 14.6 mM (5 gl⁻¹) sucrose it has been possible to produce vigorous and true-to-type plants with a multiplication factor of approximately 2.6 per 6 wk.     

Multiple Effects of Viscosity,Water Activity and Glass Transition Temperature on Peroxidase Activity in Binary and Ternary Carbohydrate Solutions

The individual and combined effects of water activity (a_w), bulk viscosity and glass transition temperature (Tg’) on the activity of horseradish peroxidase (HRP) in buffered sugars (glucose, trehalose and maltose) and maltodextrin solutions were investigated. Viscosity was the most important factor in the inhibition of HRP activity; however, when Tg’ was changed by the using solutes with different molecular weight, it became a key factor in the modulation of enzyme activity. Viscosity being equal, the sugar addition to maltodextrin solution lowered a_w and lowered Tg’ causing an increase of the enzymatic activity. Nevertheless, an inhibition of the HRP activity occurred when a_w values of 0.87 were reached due to the addition of glucose, which, among the tested sugars, showed the lowest molecular weight. Among disaccharides, maltose was more effective than trehalose in impairing the enzyme activity both in binary and ternary systems, and this is due to a non competitive biochemical inhibition exerted by this sugar on HRP. When compared to glucose, maltose and trehalose were more effective in reducing HRP activity only in the low viscosity range whilst in the high viscosity range (1–4 10^?6 m² s^?1) glucose, despite its lower Tg’ value, was slightly more efficient than disaccharides due to its a_w lowering effect.     

Effect of Carbon Source on the Shoot Proliferation Potential of Epicotyl Explants of Syzygium cuminii

Black plum (Syzygium cuminii) explants were grown in vitro on Murashige and Skoog medium. Among the various saccharides tested, the best caulogenic response was afforded by sucrose both in terms of explant response and shoot developing potential. Within monosaccharides, mannose was totally inhibitory as on the medium supplemented with this the shoot buds failed to develop, while, fructose and xylose completely inhibited the opening as well as the elongation of shoot buds. Glucose and galactose did not completely inhibit the caulogenic response. Among disaccharides, other than sucrose, maltose totally inhibited the elongation of the developed shoot buds while lactose supported it to a limited extent. Sugar alcohols, though not as good as sucrose, proved better sources of carbon and energy than the other tested sugars. Sucrose at concentration 4 % proved to be the best in developing 4.2 shoots per explant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selective inhibition of sweetness by the sodium salt of +/-2-(4-methoxyphenoxy)propanoic acid.

The purpose of this study was to determine the degree to which the sodium salt of +/-2-(4-methoxyphenoxy)propanoic acid (Na-PMP) reduced sweet intensity ratings of 15 sweeteners in mixtures. Na-PMP has been approved for use in confectionary/frostings, soft candy and snack products in the USA at concentrations up to 150 p.p.m. A trained panel evaluated the effect of Na-PMP on the intensity of the following 15 sweeteners: three sugars (fructose, glucose, sucrose), three terpenoid glycosides (monoammonium glycyrrhizinate, rebaudioside-A, stevioside), two dipeptide derivatives (alitame, aspartame), two N-sulfonylamides (acesulfame-K, sodium saccharin), two polyhydric alcohols (mannitol, sorbitol), 1 dihydrochalcone (neohesperidin dihydrochalcone), one protein (thaumatin) and one sulfamate (sodium cyclamate). Sweeteners were tested at concentrations isosweet with 2.5, 5, 7.5 and 10% sucrose in mixtures with two levels of Na-PMP: 250 and 500 p.p.m. In addition, the 15 sweeteners were tested either immediately or 30 s after a pre-rinse with 500 p.p.m. Na-PMP. In mixtures, Na-PMP at both the 250 and 500 p.p.m. levels significantly blocked sweetness intensity for 12 of the 15 sweeteners. However, when Na-PMP was mixed with three of the 15 sweeteners (monoammonium glycyrrhizinate, neohesperidin dihydrochalcone and thaumatin), there was little reduction in sweetness intensity. Pre-rinsing with Na-PMP both inhibited and enhanced sweetness with the greatest enhancements found for monoammonium glycyrrhizinate, neohesperidin dihydrochalcone and thaumatin, which were not suppressed by Na-PMP in mixtures. The mixture data suggest that Na-PMP is a selective competitive inhibitor of sweet taste. The finding that pre-treatment can produce enhancement may be due to sensitization of sweetener receptors by Na-PMP.     

Effect of maltose on glucoamylase formation by Aspergillus niger

Low levels of glucoamylase are produced when Aspergillus niger is grown on sorbitol, but substitution of the latter by glucose, maltose, or starch results in greater formation of glucoamylase as measured by enzymatic activity. Both glucoamylase I and glucoamylase II are formed in a yeast extract medium; however, glucoamylase I appears to be the only form produced when ammonium chloride is the nitrogen source. Maltose or isomaltose (1.4 x 10(-4)m), but no other disaccharides or monosaccharides, dextrins, dextrans, or starches, stimulated glucoamylase formation when added to mycelia pregrown on sorbitol-ammonium salts. The induction of glucoamylase by maltose was independent of sulfate concentration but showed a dependency on low pH and the absence of utilizable carbon sources.     

Allelic variation of the Tas1r3 taste receptor gene selectively affects taste responses to sweeteners: evidence from 129.B6-Tas1r3 congenic mice.

The Tas1r3 gene encodes the T1R3 receptor protein, which is involved in sweet taste transduction. To characterize ligand specificity of the T1R3 receptor and the genetic architecture of sweet taste responsiveness, we analyzed taste responses of 129.B6-Tas1r3 congenic mice to a variety of chemically diverse sweeteners and glucose polymers with three different measures: consumption in 48-h two-bottle preference tests, initial licking responses, and responses of the chorda tympani nerve. The results were generally consistent across the three measures. Allelic variation of the Tas1r3 gene influenced taste responsiveness to nonnutritive sweeteners (saccharin, acesulfame-K, sucralose, SC-45647), sugars (sucrose, maltose, glucose, fructose), sugar alcohols (erythritol, sorbitol), and some amino acids (D-tryptophan, D-phenylalanine, L-proline). Tas1r3 genotype did not affect taste responses to several sweet-tasting amino acids (L-glutamine, L-threonine, L-alanine, glycine), glucose polymers (Polycose, maltooligosaccharide), and nonsweet NaCl, HCl, quinine, monosodium glutamate, and inosine 5'-monophosphate. Thus Tas1r3 polymorphisms affect taste responses to many nutritive and nonnutritive sweeteners (all of which must interact with a taste receptor involving T1R3), but not to all carbohydrates and amino acids. In addition, we found that the genetic architecture of sweet taste responsiveness changes depending on the measure of taste response and the intensity of the sweet taste stimulus. Variation in the T1R3 receptor influenced peripheral taste responsiveness over a wide range of sweetener concentrations, but behavioral responses to higher concentrations of some sweeteners increasingly depended on mechanisms that could override input from the peripheral taste system.     

Identification of new qingyangshengenin and caudatin glycosides from the roots of Cynanchum otophyllum

HPLC analysis of the roots of Cynanchum otophyllum Scheind (Asclepiadaceae) led to the isolation of six new pregnane glycosides, specifically otophyllosides N-P (2-4) and otophyllosides Q-S (7-9), in addition to the identification of three known C-21 steroidal glycosides, otophylloside A (1), otophylloside B (5) and caudatin 3-O-β-D-glucopyranosyl-(1→4)-β-D-oleandropyranosyl-(1→4)-β-D-cymaropyranosyl-(1→4)-β-D-cymaropyranoside (6). The structure of each glycoside was determined by detailed spectroscopic analysis and chemical methods. All compounds contain qingyangshengenin or caudatin aglycones and a straight sugar chain consisting of 4-7 hexosyl moieties with the mode of 1→4 linkage. The optically isomeric monosaccharides, D- and L-cymarose, coexisted in both otophyllosides R (8) and S (9).