Preferences and apparent digestibilities of sugars by fruit damaging birds in Japan

Gray starlings Sturnus cineraceus, azure-winged magpies Cyanopica cyana and brown-eared bulbuls Hypsipetes amaurotis are among the main bird pests in commercial fruit orchards in central Japan. Recently Brugger & Nelms (1991) suggested that developing high-sucrose fruit cultivars could reduce crop damage, because some pest birds lack the enzyme sucrase and can develop an aversion to sucrose. Preferences for, and digestibilities of, the monosaccharides glucose and fructose and the disaccharide sucrose by these pests species were therefore studied to assess whether this idea would be applicable in central Japan. Gray starlings and brown-eared bulbuls were able to detect glucose, fructose, a mixture of glucose and fructose, and sucrose at a concentration of 12% w/v. Azure-winged magpies also detected glucose and fructose, but failed to detect sucrose at the same concentration. In pairwise preference trials gray starlings and azure-winged magpies selected the monosaccharides over sucrose, but brown-eared bulbuls did not. To estimate the digestibility of the sugars the apparent assimilated mass coefficient, AMC*, was calculated for each species eating each sugar by measuring intake and faecal output. Monosaccharides had mean AMC*s of 0.77, 0.96 and 0.92 when consumed by gray starlings, azure-winged magpies and brown-earned bulbuls respectively. AMC* values for sucrose were 0.82 and 0.49 for brown-eared bulbuls and azure-winged magpies respectively, but gray starlings were shown to be unable to digest sucrose. As AMC* values varied from 0.75 to 0.97, consumption rates of sugars increased as digestibility decreased. Although increasing sucrose contents of commercial fruits may deter sucrase-deficient birds such as gray starlings from depredating fruits, it may also lead to increased crop damage by species such as the azure-winged magpie and brown-eared bulbul which may have to consume more of the less digestible fruit in order to meet their energy requirements.     

In Vitro Sugar Transport in Zea mays L. Kernels : I. Characteristics of Sugar Absorption and Metabolism by Developing Maize Endosperm

Short-term transport studies were conducted using excised whole Zea mays kernels incubated in buffered solutions containing radiolabeled sugars. Following incubation, endosperms were removed and rates of net ¹⁴C-sugar uptake were determined. Endogenous sugar gradients of the kernel were estimated by measuring sugar concentrations in cell sap collected from the pedicel and endosperm. A sugar concentration gradient from the pedicel to the endosperm was found. Uptake rates of ¹⁴C-labeled glucose, fructose, and sucrose were linear over the concentration range of 2 to 200 millimolar. At sugar concentrations greater than 50 millimolar, hexose uptake exceeded sucrose uptake. Metabolic inhibitor studies using carbonylcyanide-m-chlorophenylhydrazone, sodium cyanide, and dinitrophenol and estimates of Q₁₀ suggest that the transport of sugars into the developing maize endosperm is a passive process. Sucrose was hydrolyzed to glucose and fructose during uptake and in the endosperm was either reconverted to sucrose or incorporated into insoluble matter. These data suggest that the conversion of sucrose to glucose and fructose may play a role in sugar absorption by endosperm. Our data do not indicate that sugars are absorbed actively. Sugar uptake by the endosperm may be regulated by the capacity for sugar utilization (i.e. starch synthesis).     

The Complement of Soluble Sugars in the Saccharum Complex

The use of sugarcane as a biofactory and source of renewable biomass is being investigated increasingly due to its vigorous growth and ability to fix a large amount of carbon dioxide compared to other crops. The high biomass resulting from sugarcane production (up to 80 t/ha) makes it a candidate for genetic manipulation to increase the production of other sugars found in this research that are of commercial interest. Sucrose is the major sugar measured in sugarcane with hexoses glucose and fructose present in lower concentrations; sucrose can make up to 60% of the total dry weight of the culm. Species related to modern sugarcane cultivars were examined for the presence of sugars other than glucose, fructose and sucrose with the potential of this crop as a biofactory in mind. The species examined form part of the Saccharum complex, a closely-related interbreeding group. Extracts of the immature and mature internodes of six different species and a hybrid were analysed with gas chromatography mass spectrometry to identify mono-, di- and tri-saccharides, as well as sugar acids and sugar alcohols. Thirty two sugars were detected, 16 of which have previously not been identified in sugarcane. Apart from glucose, fructose and sucrose the abundance of sugars in all plants was low but the research demonstrated the presence of sugar pathways that could be manipulated. Since species from the Saccharum complex can be interbred, any genes leading to the production of sugars of interest could be introgressed into commercial Saccharum species or manipulated through genetic engineering.     

Carbon catabolite repression of invertase during batch cultivations of Saccharomyces cerevisiae: the role of glucose, fructose, and mannose

When Saccharomyces cerevisiae are grown on a mixture of glucose and another fermentable sugar such as sucrose, maltose or galactose, the metabolism is diauxic, i.e. glucose is metabolized first, whereas the other sugars are metabolized when glucose is exhausted. This phenomenon is a consequence of glucose repression, or more generally, catabolite repression. Besides glucose, the hexoses fructose and mannose are generally also believed to trigger catabolite repression. In this study, batch fermentations of S. cerevisiae in mixtures of sucrose and either glucose, fructose or mannose were performed. It was found that the utilization of sucrose is inhibited by concentrations of either glucose or fructose higher than 5 g/l, and thus that glucose and fructose are equally capable of exerting catabolite repression. However, sucrose was found to be hydrolyzed to glucose and fructose, even when the mannose concentration was as high as 17 g/l, indicating, that mannose is not a repressing sugar. It is suggested that the capability to trigger catabolite repression is connected to hexokinase PII, which is involved in the in vivo phosphorylation of glucose and fructose. Received: 5 May 1998 / Received revision: 3 August 1998 / Accepted: 8 August 1998     

Evaluating potential sugar food sources from the olive grove agroecosystems for Prays oleae parasitoid Chelonus elaeaphilus

Chelonus elaeaphilus Silvestri (Hymenoptera: Braconidae) is a host-specific parasitoid of the olive moth, Prays oleae (Bernard), that can cause parasitism rates of up to 80% in Mediterranean olive groves. A laboratory study was carried out to assess the potential of sugars provided by wild plant species in olive grove agroecosystem to enhance the fitness of C. elaeaphilus. Insects were reared in a climate-controlled chamber at 25?±?2°C, 60?±?5% relative humidity (RH) with a photoperiod of 16:8 (L:D) h. Five naturally occurring wild plant nectar sugars (sucrose, fructose, glucose, maltose and mannose) were tested for their effect on insect longevity. The nectar sugar content of sucrose, fructose and glucose in 12 selected olive grove agroecosystem plant species was analysed and categorised on the basis of sugar ratios. Female insect longevity was increased when they were fed on both sucrose and glucose compared to either maltose or fructose, suggesting that sucrose-dominant nectars would bene?t this parasitoid. Sucrose was predominant in the nectar of five of the studied plant species (Silene gallica, Borago officinalis, Echium plantagineum, Lavandula stoechas and Lonicera hispânica). The results are discussed in terms of potential enhancement of the biological control of P. oleae.     

Antennal sugar sensitivity in the click beetle Agriotes obscurus

The occurrence of salt‐, sugar‐sensitive neurones and a mechanoreceptor neurone in the antennal hair‐like gustatory sensilla of the click beetle Agriotes obscurus L. (Coleoptera, Elateridae) is demonstrated using the electrophysiological sensillum tip‐recording technique. The stimulating effect of 13 water soluble sugars at 100 mm is tested on the neurones of these sensilla. Sucrose and fructose are the two most stimulating sugars for the sugar‐sensitive neurone, evoking almost 30 spikes s^?1 at 100 mm . The stimulating effect of arabinose, glucose, mannose, maltose and raffinose is three‐ to five‐fold lower, in the range 5.9–9.6 spikes s^?1. The remaining six sugars, xylose, galactose, rhamnose, cellobiose, trehalose and lactose, have very low (<1 spikes s^?1) or no ability to stimulate the sugar‐sensitive neurone. Concentration/response curves of the sugar‐sensitive neurone to sucrose, fructose and glucose at 0.01–100 mm overlap to a large extent in hibernating, cold reactivated and reproductively‐active beetles. A remarkable 9–50% decrease in the number of spikes evoked by 100 mm fructose and 10–100 mm sucrose occurs, however, in reproductively‐active beetles in June compared with beetles at the beginning of hibernation in October. These findings show that A. obscurus is capable of sensing a wide range sugars via their antennal gustatory sensilla.     

The influence of type and concentration of the carbon source on production of citric acid by Aspergillus niger

Summary The influence of various carbon sources and their concentration on the production of citrate by Aspergillus niger has been investigated. The sugars maltose, sucrose, glucose, mannose and fructose (in the given order) were carbon sources giving high yields of citric acid. Optimal yields were observed at sugar concentrations of 10% (w/v), with the exception of glucose (7.5%). No citric acid was produced on media containing less than 2.5% sugar. Precultivation of A. niger on 1% sucrose and transference to a 14% concentration of various other sugars induced citrate accumulation. This could be blocked by the addition of cycloheximide, an inhibitor of de novo protein synthesis. This induction was achieved using maltose, sucrose, glucose, mannose and fructose, and also by some other carbon sources (e.g. glycerol) that gave no citric acid accumulation in direct fermentation. Precultivation of A. niger at high (14%) sucrose concentrations and subsequent transfer to the same concentrations of various other carbohydrates, normally not leading to citric acid production, led to formation of citrate. Endogenous carbon sources were also converted to citrate under these conditions. A 14%-sucrose precultivated mycelium continued producing some citrate upon transfer to 1% sugar. These results indicate that high concentrations of certain carbon sources are required for high citrate yields, because they induce the appropriate metabolic imbalance required for acidogenesis.     

Optimization of butanol production from tropical maize stalk juice by fermentation with Clostridium beijerinckii NCIMB 8052

Mixed sugars from tropical maize stalk juice were used to carry out butanol fermentation with Clostridium beijerinckii NCIMB 8052. Batch experiments employing central composite design (CCD) and response surface methodology (RSM) optimization were performed to evaluate effects of three factors, i.e. pH, initial total sugar concentration, and agitation rate on butanol production. Optimum conditions of pH 6.7, sugar concentration 42.2 g/L and agitation rate 48 rpm were predicted, under which a maximum butanol yield of 0.27 g/g-sugar was estimated. Further experiments demonstrated that higher agitation facilitated acetone production, leading to lower butanol selectivity in total acetone–butanol–ethanol (ABE). While glucose and fructose are more preferable by C. beijerinckii, sucrose can also be easily degraded by the microorganism. This study indicated that RSM is a useful approach for optimizing operational conditions for butanol production, and demonstrated that tropical maize, with high yield of biomass and stalk sugars, is a promising biofuel crop.     

The effect of season of growth on the chemical composition of cambial saps of Eucalyptus regnans trees

Summary Bark was stripped, at monthly intervals, from the stems of ten previously-unsampled trees of Eucalyptus regnans F. Muell. The exposed surfaces of inner phloem and outer xylem yielded phloem and cambial saps which were rapidly frozen. After freeze drying to determine the contents of water and dry-matter, the samples were extracted with 80% ethanol. The main components in this extract are low molecular weight carbohydrates and salts of inorganic acids. The carbohydrates comprise stachyose, raffinose, sucrose, galactinol, glucose, fructose, myo-inositol and galactose; sucrose is invariably the major component. The amounts of all components varied widely during the sampling period. Multiple regression analyses showed that season of growth has a significant effect on sucrose, glucose, fructose, total sugars and soluble dry-matter, maxima being recorded near the beginning of autumn and spring, and minima near the beginning of winter and summer; that oligosaccharide and myoinositol contents are significantly related to atmospheric temperature; and that rainfall has a significant effect on the hexose and total sugar contents, saps from the xylem surfaces being more affected than those from the phloem surfaces. The translocated photosynthates in E. regnans appear to be oligosaccharides of the raffinose family and sucrose. Significant negative correlations between oligosaccharides and both sucrose and myoinositol, and significant positive correlations between sucrose and both glucose and fructose, are consistent with enzymic hydrolysis and resynthesis of most di- and oligosaccharides. The biosynthetic demands of developing secondary tissues and/or the fluctuations in composition of sieve-tube assimilates appear to control the composition of the sugars in the saps. Oligosaccharides and sucrose may function as soluble reserve substances as well as translocated photosynthates. It is possible that myoinositolis a key component in the interconversion processes of the sugars; experiments with radioactive sugars tend to lend support to this contention, especially during winter conditions.     

The regulation of sugar uptake and accumulation in bean pod tissue

The identity, localization and physiological significance of enzymes involved in sugar uptake and accumulation were determined for endocarp tissue of pods of Kentucky Wonder pole beans (Phaseolus vulgaris). An intracellular, alkaline invertase (pH optimum, 8) was assayed in extracted protein, as well as enzymes involved in sucrose synthesis, namely, uridinediphosphate (UDP-glucose pyrophosphorylase and UDP-glucose-fructose transglucosylase). Indirect evidence indicated the presence also of hexokinase, phosphohexoseisomerase and phosphoglucomutase. The data suggested that sucrose synthesis occurred in the cytoplasm, and that both sugar storage and an alkaline invertase occurred in the vacuole. The latter functions to hydrolyze accumulated sucrose. An outer space invertase (pH optimum, 4.0) was detected, but was variable in occurrence. Although its activity at the cell surface enhanced sucrose uptake, sucrose may be taken up unaltered.

Over a wide range of concentrations of exogenous glucose the sucrose/reducing sugar ratio of accumulated sugars remained unchanged at about 20. Synthesis of sucrose appears to be requisite to initial accumulation from glucose or fructose, as free hexoses do not increase at the apparent saturating concentration for uptake. Sucrose accumulation from exogenous hexose represents a steady-state value, in which sucrose is transported across the tonoplast into the vacuole at a rate equivalent to its rate of synthesis. Evidence indicates that this component of the accumulation process involves active transport of sucrose against a concentration gradient. The ratio of sucrose/reducing sugars in the accumulated sugars immediately after a period of uptake was inversely related to the level of inner space invertase. Within 16 hours after a period of accumulation, practically all of the sugar occurs as glucose and fructose.

The absence of competition among hexoses and sucrose indicated that a common carrier was not involved in their uptake. From a series of studies on the kinetics of uptake of glucose and fructose, including competition studies, the effects of inhibitors, radioactive assay of accumulated sugars and the distribution of label in accumulated sucrose it appeared that rate limitation for glucose or fructose uptake resides in the sequence of reactions leading to sucrose synthesis, rather than in a process mediated by a carrier protein.

     

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。     

A cell wall invertase controls nectar volume and sugar composition

Nectar volume and sugar composition are key determinants of the strength of plant–pollinator mutualisms. The main nectar sugars are sucrose, glucose and fructose, which can vary widely in ratio and concentration across species. Brassica spp. produce a hexose-dominant nectar (high in the monosaccharides glucose and fructose) with very low levels of the disaccharide sucrose. Cell wall invertases (CWINVs) catalyze the irreversible hydrolysis of sucrose into glucose and fructose in the apoplast. We found that BrCWINV4A is highly expressed in the nectaries of Brassica rapa. Moreover, a brcwinv4a null mutant: (i) has greatly reduced CWINV activity in the nectaries; (ii) produces a sucrose-rich nectar; but (iii) with significantly less volume. These results definitively demonstrate that CWINV activity is not only essential for the production of a hexose-rich nectar, but also support a hypothetical model of nectar secretion in which its hydrolase activity is required for maintaining a high intracellular-to-extracellular sucrose ratio that facilitates the continuous export of sucrose into the nectary apoplast. The extracellular hydrolysis of each sucrose into two hexoses by BrCWINV4A also likely creates the osmotic potential required for nectar droplet formation. These results cumulatively indicate that modulation of CWINV activity can at least partially account for naturally occurring differences in nectar volume and sugar composition. Finally, honeybees prefer nectars with some sucrose, but wild-type B. rapa flowers were much more heavily visited than flowers of brcwinv4a, suggesting that the potentially attractive sucrose-rich nectar of brcwinv4a could not compensate for its low volume.     

The effect of sugars on inverse relation between the growth and chlorophy11 synthesis in tobacco tissue

Cytokinin-dependent and cytokinin-autonomous strains of tobacco callus tissue (Nicotiana tabacum L. cv. ‘Wisconsin 38’) were grown on media containing sucrose, glucose and fructose, respectively. The tissues were kept 14 days in darkness and then transferred for 9 days to continuous light after which time the fresh weight and chlorophyll content were estimated. The highest chlorophyll concentration was recorded at sugar levels which were either suboptimal (sucrose in the case of cytokinin-dependent strain) or supraoptimal (all other sugars for both strains and sucrose for the cytokinin-autonomous strain) for tissue growth. The chlorophyll concentration was increased when the tissue was cultured on media containing glucose or fructose,i.e. sugars whioh did not support the growth as well as sucrose. Chlorophyll synthesis in the cytokinin-autonomous strain is significantly lower than in the cytokinin-dependent strain. This difference was independent of either sugar source or concentration. These results support the observed inverse relationship between tissue growth and plastid development and the limited metabolic activity of plastids in cytokinin-autonomous tissues.     

Sugar utilization by yeast during fermentation

Summary When glucose and fructose are fermented separately, the uptake profiles indicate that both sugars are utilized at similar rates. However, when fermentations are conducted in media containing an equal concentration of glucose and fructose, glucose is utilized at approximately twice the rate of fructose. The preferential uptake of glucose also occurred when sucrose, which was first rapidly hydrolyzed into glucose and fructose by the action of the enzyme invertase, was employed as a substrate. Similar results were observed in the fermentation of brewer's wort and wort containing 30% sucrose and 30% glucose as adjuncts. In addition, the high levels of glucose in the wort exerted severe catabolite repression on maltose utilization in theSaccharmyces uvarum (carlsbergensis) brewing strain. Kinetic analysis of glucose and fructose uptake inSaccharomyces cerevisiae revealed aK _m of 1.6 mM for glucose and 20 mM for fructose. Thus, the yeast strain has a higher affinity for glucose than fructose. Growth on glucose or fructose had no repressible effect on the uptake of either sugar. In addition, glucose inhibited fructose uptake by 60% and likewise fructose inhibited, glucose uptake by 40%. These results indicate that glucose and fructose share the same membrane transport components.     

Genome-wide annotation and functional identification of aphid GLUT-like sugar transporters

Background

Phloem feeding insects, such as aphids, feed almost continuously on plant phloem sap, a liquid diet that contains high concentrations of sucrose (a disaccharide comprising of glucose and fructose). To access the available carbon, aphids hydrolyze sucrose in the gut lumen and transport its constituent monosaccharides, glucose and fructose. Although sugar transport plays a critical role in aphid nutrition, the molecular basis of sugar transport in aphids, and more generally across all insects, remains poorly characterized. Here, using the latest release of the pea aphid, Acyrthosiphon pisum, genome we provide an updated gene annotation and expression profile of putative sugar transporters. Finally, gut expressed sugar transporters are functionally expressed in yeast and screened for glucose and fructose transport activity.

Results

In this study, using a de novo approach, we identified 19 sugar porter (SP) family transporters in the A. pisum genome. Gene expression analysis, based on 214, 834 A. pisum expressed sequence tags, supports 17 sugar porter family transporters being actively expressed in adult female aphids. Further analysis, using quantitative PCR identifies 4 transporters, A. pisum sugar transporter 1, 3, 4 and 9 (ApST1, ApST3, ApST4 and ApST9) as highly expressed and/or enriched in gut tissue. When expressed in a Saccharomyces cerevisiae hexose transporter deletion mutant (strain EBY.VW4000), only ApST3 (previously characterized) and ApST4 (reported here) transport glucose and fructose resulting in functional rescue of the yeast mutant. Here we characterize ApST4, a 491 amino acid protein, with 12 predicted transmembrane regions, as a facilitative glucose/fructose transporter. Finally, phylogenetic reconstruction reveals that ApST4, and related, as yet uncharacterized insect transporters are phylogenetically closely related to human GLUT (SLC2A) class I facilitative glucose/fructose transporters.

Conclusions

The gut enhanced expression of ApST4, and the transport specificity of its product is consistent with ApST4 functioning as a gut glucose/fructose transporter. Here, we hypothesize that both ApST3 (reported previously) and ApST4 (reported here) function at the gut interface to import glucose and fructose from the gut lumen.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-647) contains supplementary material, which is available to authorized users.     

Simultaneous consumption of glucose and fructose from sugar mixtures during batch growth of Corynebacterium glutamicum

Growth of Corynebacterium glutamicum on mixtures of glucose and fructose leads to simultaneous consumption of both sugars in which the uptake of each sugar is directly related to the expression of the corresponding sugar uptake mechanism. The overall rate of sugar uptake was higher on sugar mixtures than on either glucose or fructose alone and was similar to that observed during sucrose metabolism. The results suggest that sugar uptake limits metabolic rates though, in the case of fructose, overflow metabolism of both lactate and dihydroxyacetone was observed. Such products could reflect a higher flux through glycolysis rather than the pentose pathway during catabolism of fructose. Received: 24 October 1996 / Received revision: 10 January 1997 / Accepted: 10 January 1997     

Influence of the carbon source on growth and rosmarinic acid production in suspension cultures of Coleus blumei

Suspension cultures of Coleus blumei were characterized with respect to growth and rosmarinic acid formation in media with different sugars and various sugar concentrations. Sucrose is the sugar with the highest stimulating effect on growth and rosmarinic acid accumulation, followed by glucose and fructose. The sugar alcohol mannitol cannot be metabolized by the plant cells. Sucrose is cleaved into glucose and fructose by the Coleus cells. Sucrose concentrations from 1 to 5% have an increasing positive effect on growth and rosmarinic acid synthesis in the cell cultures with a maximum rosmarinic acid content of 12% of the dry weight in medium with 5% sucrose; in medium with 6% sucrose rosmarinic acid accumulation obviously did not reach its highest level in the culture period of 14 days. A very high yield of rosmarinic acid (2 mg ml^-1 suspension) could also be achieved by maintaining a sucrose concentration of 2% during the whole culture period. The start of rosmarinic acid synthesis by the cell cultures seems to be regulated by the growth limitation when a nutrient, e.g. phosphate is depleted from the medium. The rate of rosmarinic acid accumulation is related to the amount of carbon left in the medium when growth ceases.Abbreviations RA rosmarinic acid     

Sugars in crop plants

We review current knowledge of the most abundant sugars, sucrose, maltose, glucose and fructose, in the world's major crop plants. The sucrose‐accumulating crops, sugar beet and sugar cane, are included, but the main focus of the review is potato and the major cereal crops. The production of sucrose in photosynthesis and the inter‐relationships of sucrose, glucose, fructose and other metabolites in primary carbon metabolism are described, as well as the synthesis of starch, fructan and cell wall polysaccharides and the breakdown of starch to produce maltose. The importance of sugars as hormone‐like signalling molecules is discussed, including the role of another sugar, trehalose, and the trehalose biosynthetic pathway. The Maillard reaction, which occurs between reducing sugars and amino acids during thermal processing, is described because of its importance for colour and flavour in cooked foods. This reaction also leads to the formation of potentially harmful compounds, such as acrylamide, and is attracting increasing attention as food producers and regulators seek to reduce the levels of acrylamide in cooked food. Genetic and environmental factors affecting sugar concentrations are described.     

Metabolism of free sugars in relation to starch synthesis in the developing Sorghum vulgare grain

Accumulation of starch at expense of its free-sugar precursors was studied in the developing grains of the ‘SL-44’variety of Sorghum vulgare Pers. The content of starch gradually increased with the maturation of the grain and this increase was relatively fast until 18 days after anthesis. The daily rate of starch accumulation was at a maximum 15 days after anthesis. The content of total free sugars, reducing sugars, non-reducing sugars other than sucrose, total and non-sucrosyl fructose, and glucose also increased, reaching maximum values at 18 days after anthesis. Sucrose content gradually increased with a concomitant decrease in the activity of invertase, and sucrose was the major non-reducing sugar in the matured grains. Detached heads incubated in labelled sugars indicated that, compared to sucrose and fructose. ¹⁴C was more efficiently incorporated from glucose into grain starch, which was maximally synthesized at the mid-milky stage of grain development. Exogenous supply of NAD⁺ plus ATP stimulated the in vivo incorporation of ¹⁴C from sucrose to starch. The decline in the rate of starch accumulation did not synchronise with that of protein synthesis.     

Nectar sugars enhance fitness in male Coenonympha pamphilus butterflies by increasing longevity or realized reproduction

The principal components of floral nectar are water and the sugars sucrose, fructose and glucose. Several studies have shown the importance of nectar sugars for female butterfly fecundity, whereas to date little attention has been paid to the effect of nectar sugars on male butterfly reproduction. Clear evidence for an effect of nectar sugars on male realized reproductive success is still missing. In this study, we fed male Coenonympha pamphilus butterflies nectar mimics with low (5%), medium (20%) or high (30%) total sugar concentrations with a sucrose:glucose:fructose ratio of 2.7:1.1:1. Sugar solutions were made mimicking Knautia arvensis, an essential nectar plant for C. pamphilus and many other European butterflies. Realized male reproductive success for each treatment was measured indirectly via nuptial gifts, by recording reproductive parameters and by characterizing time patterns over the oviposition period of their female partner. Male butterflies fed high‐concentrated nectar sugars had a longer lifespan than males fed low‐concentrated nectar sugars. In contrast, offspring of males fed medium‐concentrated nectar sugars had a higher hatching mass than progeny of males fed low‐concentrated nectar sugars, indicating a tradeoff between somatic maintenance and reproduction in the use of nectar sugars. Thus, allocation patterns of nectar sugars differed according to sugar concentrations in adult food. The method used in this experiment took into account the indispensable role of female butterflies in passing male nutrients to offspring. With this comprehensive approach, we can show the general importance of nectar sugars for male butterfly fitness and support previous findings suggesting a coevolutionary process between butterflies and flowers dependent on butterfly pollination.