Preferences for nectar sugars in the peacock butterfly, Inachis io
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1. Peacock butterflies, Inachis io , were tested experimentally for their preferences for nectar sugars. 2. In tests with different plain sugar solutions (25%, weight to total weight) the butterflies strongly preferred sucrose and fructose over glucose. They also preferred sucrose over fructose. 3. In tests with mixed sugar solutions the butterflies clearly preferred both sucrose‐dominant (sucrose : hexoses = 5 : 1) and balanced sugar solutions (sucrose : glucose : fructose = 1 : 1 : 1) over hexose‐dominant sugar solutions (sucrose : hexoses = 1 : 5). 4. Females consumed significantly more of the balanced sugar solution than did males. 5. These results are discussed with respect to previous experiments on nectar preferences of butterflies, nectar sugar composition of butterfly‐pollinated flowers, and flower preferences, physiological and reproductive aspects of butterflies.Keywords:
Hexose
Tonoplast vesicles were prepared from the flesh tissue of mature pear fruit. Sugar uptakes into the vesicles determined by two different methods, the membrane and the gel filtration methods, were quite similar. The uptake was highest for glucose and subsequently, in order, for fructose, sucrose and sorbitol. It was not stimulated by addition of ATP, although the vesicles could create a proton gradient. However, the uptakes were significantly inhibited by p-chloromercuribenzene sulphonate (PCMBS, SH-reagent and inhibitor of sugar transporter). Further, the PCMBS-sensitive uptakes of glucose and fructose saturated with their increased concentrations. Thus, these PCMBS-sensitive uptakes are mediated by the transporter of facilitated diffusion. The uptakes of glucose or fructose each had two Km values. Km values for glucose were 0.35 and 18 mM, and those for fructose were 1.6 and 25 raM. The uptake of 0.2 mM glucose was inhibited by 2 mM fructose and that of 2 mM fructose was inhibited by 2 mM glucose, but neither was inhibited by sucrose or sorbitol. O-methyl-glucose (OMG) also inhibited both the glucose and fructose uptakes. Therefore, the same transporter may mediate both glucose and fructose uptakes at lower concentrations; this hexose transport system differed from the sucrose and sorbitol transport systems.
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Uptake of sugar by Phaseolus vulgaris cell suspension cultures from a sucrose supplemented medium is predominantly in the hexose form. This is due to a rapid cleavage of the sucrose by an apoplastic acid invertase activity and an apparent very low demand for and uptake of carbon from the medium prior to induction of cell growth and division. Glucose is preferentially taken up, leading to an accumulation of fructose in the medium. However, when the glucose is depleted the cells do take up the fructose at a rate similar to that of glucose. When glucose or fructose is supplied individually to cell cultures, both are utilised very efficiently with growth slightly better on the fructose medium. Hexose uptake is largely an active process with diffusion uptake even at the highest concentrations (> 50 m M ) contributing less than 30%. The hexose uptake system of the cells has a greater affinity for glucose (K m = 240 µ M ) than for fructose (K m = 960 µ M ) but the maximum uptake (V max ) is similar. The major difference in the kinetic properties of hexose uptake is that glucose is a strong inhibitor of fructose uptake, while fructose has little effect on glucose uptake. The differences in the kinetic properties of the uptake system for the two hexoses can largely explain the observed pattern of hexose utilisation when both glucose and fructose are present in the medium.
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Carbohydrate Metabolism
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1. Effects of dietary composition, energy restriction, and diabetes on hexose absorption were examined by feeding male rats isoenergetic, semi-synthetic diets of differing carbohydrate and protein content. Diets were carbohydrate, (g/kg): 890 sucrose; carbohydrate-protien, 500 sucrose, 390 casein; or protein, 890 casein. An additional group was fed on commercial rat chow ad lib. 2. Hexose (3-O-methyl-D-glucose) absorption was measured by luminal perfusion of the entire small intestine in situ. Absorption by the total small intestine, i.e. absorption per rat, and absorption per g dry weight of mucosa (specific absorption) were calculated. 3. When semi-synthetic diets were fed at 210 kJ/d to normal animals absorption depended on composition of diets: carbohydrate enhanced or protein suppressed hexose absorption. Dietary carbohydrate as glucose, dextrimaltose or starch gave the same hexose absorption response as sucrose. 4. When diets of normal rats were restricted to 118 kJ/d, specific absorption was independent of dietary composition and was increased for all dietary groups to the level of the group fed on the carbohydrate diet at 210 kJ/d. 5. When diabetic rats were given 210 kJ/d, hexose specific absorption was the same for all diabetic groups independent of dietary composition and was equal to that of controls given carbohydrate, but greater than that of protein-fed controls. 6. Thus, when two of the three stimuli (i.e. carbohydrate diet plus energy restriction or diabetes) were combined, the effect was not additive, and the response of hexose specific absorption to diabetes and energy restriction was the same: absorption was independent of dietary composition and was stimulated relative to controls fed on diets containing protein. 7. The pattern of response of total small intestinal hexose absorption to the stimuli of dietary composition, energy restriction and diabetes was similar to that of specific absorption. 8. Compared with groups given semi-synthetic diets, rats eating commercial rat chow ad lib. (approximately 286 kJ/d) showed increased mucosal mass and decreased specific absorption, but total absorption was similar to that of the carbohydrate and carbohydrate-protein-fed groups. 9. In a separate study in control rats, specific and total intestinal absorption of L-leucine did not respond to dietary composition, i.e. level of protein fed.
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Destarched tobacco-leaf disks were floated on per cent. (w/v) solutions of sucrose uniformly labelled with 14C in either the glucose or fructose moiety, and on invert sugar in which one hexose only was so labelled. The experiments were carried out in an atmosphere of oxygen at 25° C. Seventy-five per cent, of the sugar lost from the external solutions was recovered as starch, sucrose, fructose, glucose, and CO2. With sucrose as the substrate, 30 per cent, of the material was recovered as CO2 and 17 per cent. each as starch, sucrose, fructose, and glucose. With invert sugar as the substrate, 30 per cent, was again recovered as CO2 only 20 per cent. as the three sugars together, and 50 per cent. as starch. Whichever hexose was initially labelled and whether the sugar was supplied as sucrose or hexose, the relative specific activities of starch and sucrose in the leaf disks and of the CO2 evolved were equal or nearly equal to that of the sugar supplied. With sucrose as the substrate the sucrose in the disks retained its asymmetry of label, and free hexoses produced were similarly asymmetrically labelled. When invert sugar was the substrate the sucrose synthesized was strongly labelled in both moieties, as also were the free hexosea. It is concluded that fructose and glucose free or combined in sucrose were equally available for starch synthesis and CO2, formation, and that there can be no question of preferential utilization of one or other hexose. Starch and CO2 must arise from a common source in which readily formed derivatives of the hexoses are rapidly equilibrated. Free hexose cannot participate directly in either sucrose or starch synthesis. Accumulation of sugar not immediately metabolized and inversion of sucrose take place at a site remote from the common pool. A scheme to accommodate the results is discussed.
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The oxidation of 13 C-labeled glucose and fructose ingested as a preexercise meal between 180 and 90 min before exercise was measured on 6 subjects when either a placebo or sucrose was ingested during the exercise period. Labeled hexose oxidation, which occurred mainly during the first hour of exercise, was not significantly modified when sucrose was ingested, but exogenous glucose oxidation was significantly higher than exogenous fructose oxidation in both situations. The results suggest that the absorption rate of exogenous hexoses was high when exercise was initiated but diminished thereafter, and that glucose and fructose released from sucrose ingested during exercise did not compete with glucose or fructose ingested before exercise for intestinal absorption, for conversion into glucose in the liver (for fructose), or for uptake and oxidation of glucose in peripheral tissues. However, as already shown, in terms of availability for oxidation of carbohydrates provided by the preexercise meal, glucose should be favored over fructose.
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Fructolysis
Carbohydrate Metabolism
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Butterfly–flower morphological interrelationships were investigated for 108 butterfly species and 20 plants at Nagpur, India. Distinct clusters of higher taxa (families) are disclosed for butterfly morphology and significant morphological and taxonomic associations occur in nectar exploitation. Flower corolla depth generally restricts exploitation by butterflies in relation to proboscis length and butterflies with high wing load indices bias their feeding to plants with massed flowers. However, important exceptions emerge; also, a substantial number of butterflies feed on plants with massed flowers though their proboscises are of marginal length for corolla depths. These butterfly species are significantly smaller, lighter, with lower wing loading and shorter proboscis indices than species which easily access the same flowering plant species. It is suggested that small size and short proboscises could give them a competitive advantage (increased rate of nectar uptake) for exploiting nectar in such situations. The significance of the findings for conservation is discussed.
Proboscis
Morphology
Pieridae
Nymphalidae
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SummaryExperiments were conducted to evaluate whether fructose was converted to glucose during absorption in the chick. Chicks were found to absorb glucose and fructose rapidly and absorption of an orally administered dose of either hexose was essentially complete within 1 hr. Intestinal sacs incubated in vitro transported fructose from the mucosal to the serosal surface and only 17% of the hexose in the serosal fluid was glucose. Experiments with intact chicks using fructose-U-14C demonstrated that only 12% of the radioactive hexose entering the portal blood was glucose. Thus, it was concluded that only about 15% of absorbed fructose is converted to glucose during the process of absorption. However, 10 min following the intraperitoneal administration of fructose-U-14C, 97% of the hexose radioactivity in blood was present as glucose. The activity of hepatic fructokinase was observed to be high and was not influenced by fructose ingestion. It is proposed that fructose is rapidly utilized by the chick and that the liver is a major site of fructose metabolism.
Hexose
Fructolysis
Fructokinase
Carbohydrate Metabolism
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