Examining the interaction of light,nutrients and carbohydrates on seed germination and early seedling development of <Emphasis Type="Italic">Bletia purpurea</Emphasis> (Orchidaceae)

The effects of carbohydrate availability, carbohydrate source, nutrient availability and illumination on germination and early development of Bletia purpurea (Orchidaceae) seeds were investigated using asymbiotic seed germination. Of special interest was determining the minimum nutritional and light requirements for the completion of germination. Germination and development was limited when seeds were cultured in darkness without sucrose. Seeds were able to germinate under illuminated conditions even in the absence of sucrose and this effect was enhanced when mineral nutrients were incorporated into media. Sucrose, fructose, glucose and trehalose enhanced germination and seedling development while mannitol and sorbitol did not. These data suggest that carbohydrates, either as products of photosynthesis, from symbiotic fungi in situ or as exogenously supplied sugars in vitro, play an important role in regulating seed germination by fulfilling an energy requirement. This hypothesis has been often expressed but rarely satisfactorily tested. Mineral nutrients appear to be less important for germination than carbohydrates. The differential effect of sucrose, fructose, glucose and trehalose at two different concentrations on rhizoid production indicates carbohydrates may play a role in regulating rhizoid production.     

Soluble carbohydrates of Pinus sylvestris L. sapwood and heartwood

Summary The amounts of glucose, fructose, sucrose, arabinose/galactose, raffinose/stachyose and starch were investigated in the outer sapwood, innermost sapwood, transition zone and heartwood of four stems of Pinus sylvestris L. The samples were taken in October and the determination of the compounds was done enzymatically. It was not possible to distinguish arabinose from galactose and raffinose from stachyose. The amounts of glucose, fructose and sucrose were greatest in the outer sapwood and decreased gradually towards the innermost sapwood and the heartwood. In the outermost heartwood glucose, fructose and sucrose were only present in trace amounts. Raffinose/stachyose showed highest concentrations in the outer sapwood and decreased towards the heartwood. In contrast, the concentrations of arabinose/galactose increased towards the heartwood and the greatest amount was found in the inner heartwood. When identified by thin-layer chromatography (TLC), arabinose was found to be present in greater amounts than galactose. The amount of starch decreased markedly towards heartwood. However, the amounts of sugars in all the studied stems was very variable. The changes in the amounts of carbohydrates in the different zones of the stems and the possible relationships of these phenomena with heartwood formation are discussed.     

A possible rate-limiting function of chloroplast hexosemonophosphate isomerase in starch synthesis of leaves

Levels of fructose 6-phosphate and glucose 6-phosphate were measured in chloroplasts which had been isolated non-aqueously from leaves of various plants. a large decrease in the ratio of glucose 6-phosphate to fructose 6-phosphate in the light indicated considerable displacement of the hexosephosphate isomerase reaction from equilibrium in leaves of spinach and red beet which were photosynthesizing at high rates. The decrease in the ratio of glucose 6-phosphate to fructose 6-phosphate was correlated with an increase in the chloroplastic level of 3-phosphoglyceric acid, which proved to be a competitive inhibitor of chloroplast hexosephosphate isomerase. Other metabolites, especially the product of the reaction, glucose 6-phosphate, and ions in concentrations as present in the stroma under natural conditions, cause a further reduction in the rate of the forward reaction of the hexosemonophosphate isomerase. When the concentration of O₂ in air was decreased from 21 to 2%, both the rate of leaf photosynthesis and the ratio of glucose 6-phosphate to fructose 6-phosphate increased, whereas the concentration of 3-phosphoglyceric acid and starch synthesis decreased. The results are explained in terms of activation of ADPglucose pyrophosphorylase and of inhibition of hexosephosphate isomerase by 3-phosphoglyceric acid. Hexosephosphate isomerase appears to assume a rate-limiting function in starch synthesis in the light when ADPglucose pyrophosphorylase is activated.     

Conversion of starch into ethanol by Clostridium thermohydrosulfuricum

Summary Production of ethanol from starch by Clostridium thermohydrosulfuricum was compared with that from glucose, fructose or maltose in batch fermentations. Optimal substrate concentration and pH for ethanol production were determined. The rate of ethanol production on starch was about the same as that on glucose or fructose and overall yields were also similar (about 1.6 mol ethanol per mol glucose or glucose equivalent). Maltose was not an effective substrate for growth and ethanol production.When a mixture of starch and glucose in equal amounts was used, breakdown of starch and utilization of glucose were simultaneous. When starch and fructose were supplied together, the fructose was utilized but no hydrolysis of starch was observed. With a mixture of glucose and fructose, uptake of fructose preceeded that of glucose.     

Stimulation of L-tryptophan transport by di- and polysaccharides in the small intestine of chicks

In in vivo and in vitro experiments the effect of various carbohydrates on the absorption of L-tryptophan in the chick small intestine was investigated. On feeding the chicks with semisynthetic diet containing 58.5% of carbohydrates a stimulatory effect of glucose, particularly of starch and saccharose, on the entry of L-tryptophan into the portal vein from the chick gastrointestinal tract has been found. Using an in vitro technique the activating effect of starch and disaccharides (maltose, saccharose) on the intestinal transport of L-tryptophan was detected while monosaccharides (glucose, fructose) at different concentrations had no effect on this process or inhibited it. The possibility that energy of disaccharide hydrolysis is used to stimulate transport process is discussed.     

Leaf Carbon Metabolism and Metabolite Levels during a Period of Sinusoidal Light

Photosynthesis rate, internal CO₂ concentration, starch, sucrose, and metabolite levels were measured in leaves of sugar beet (Beta vulgaris L.) during a 14-h period of sinusoidal light, which simulated a natural light period. Photosynthesis rate closely followed increasing and decreasing light level. Chloroplast metabolite levels changed in a manner indicating differential activation of enzymes at different light levels. Starch levels declined during the first and last 2 hours of the photoperiod, but increased when photosynthesis rate was greater than 50% of maximal. Sucrose and sucrose phosphate synthase levels were constant during the photoperiod, which is consistent with a relatively steady rate of sucrose synthesis during the day as observed previously (BR Fondy et al. [1989] Plant Physiol 89: 396-402). When starch was being degraded, glucose 1-phosphate level was high and there was a large amount of glucose 6-phosphate above that in equilibrium with fructose 6-phosphate, while fructose 6-phosphate and triose-phosphate levels were very low. Likewise, the regulatory metabolite, fructose, 2,6-bisphosphate was high, indicating that little carbon could move to sucrose from starch by the triose-phosphate pathway. These data cast doubt upon the feasibility of significant carbon flow through the triose-phosphate pathway during starch degradation and support the need for an additional pathway for mobilizing starch carbon to sucrose.     

Interaction Between Dietary Carbohydrate and Copper Nutriture on Lipid Peroxidation in Rat Tissues

The effects of the interactions between dietary carbohydrates and copper deficiency on superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and their roles in peroxidative pathways were investigated. Weanling rats were fed diets deficient in copper and containing either 62% starch, fructose, or glucose. Decreased activity of SOD was noted in all rats fed the copper-deficient diets regardless of the nature of dietary carbohydrate. However, the decreased activity was more pronouced in rats fed fructose. Feeding the fructose diets decreased the activity of GSH-Px by 25 and 50% in the copper-supplemented and copper-deficient rats, respectively, compared to enzyme activities in rats fed similar diets containing either starch or glucose. The decreased SOD and GSH-Px activities in rats fed the fructose diet deficient in copper were associated with increased tissue per-oxidation and decreased hepatic adenosine triphosphate (ATP). When the fructose in the diet of copper-deficient rats was replaced with either starch or glucose, tissue SOD and GSH-Px activities were increased and these increases in enzyme activity were associated with a tendency toward reduced mitochondrial peroxidation when compared to the corre-sponding values for rats fed fructose throughout the experiment Dietary fructose aggrevated the symptoms associated with copper deficiency, but starch or glucose ameliorated them. The protective effects were more pronounced with starch than with glucose.     

Fatty acid synthetase activity in the liver and adipose tissue of rats fed with various carbohydrates

1. The inclusion of sucrose in the diet of rats led to an increase in hepatic fatty acid synthetase activity compared with that of rats fed with starch as the sole carbohydrate. The higher activity occurred within 18h of the introduction of sucrose and persisted with fluctuations for the 30 days of the experiment. Reversal of the diets in some rats after 21 days led to changes in the enzyme activity to values appropriate to the second diet. The plasma triglyceride concentration followed a similar pattern. 2. A comparison of the effects of diets with starch, glucose, maltose, sucrose or fructose showed that fructose gave the highest values of triglyceride content and of fatty acid synthetase activity in liver, but the lowest values of the synthetase activity in adipose tissue and the lowest values of plasma insulin concentration. These effects may perhaps be attributed to the low insulin response to fructose and to the high affinity of the liver for this sugar. 3. When the diet contained fructose or sucrose there was a correlation between hepatic synthetase activity and plasma triglyceride concentration. Neither of these, however, was related to plasma insulin concentration. On the other hand, there was a correlation between plasma insulin concentration and fatty acid synthetase activity in adipose tissue. 4. When rats were starved and then re-fed the differences in enzyme activities induced by fructose or glucose were minimized. This, together with the varying degree of difference during the course of the experiments, may explain why other workers, using the starvation-re-feeding technique and making measurements on one day only, have failed to observe differences in the activities of lipogenic enzymes in animals fed with either fructose or glucose.     

菠萝叶片绿色组织与贮水组织中代谢物水平的昼夜变化

研究了景天酸代谢(CAM)植物菠萝叶片绿色组织与贮水组织(WSP)的苹果酸、柠檬酸、异柠檬酸、淀粉、果糖、葡萄糖、蔗糖、葡糖-1-磷酸(G-1-P)、葡糖-6-磷酸(G-6-P)、果糖-6-磷酸(F-6-P)、草酰乙酸(OAA)及磷酸烯醇式丙酮酸(PEP)水平的昼夜变化。夜间苹果酸的积累仅发生在绿色组织中,表明只有绿色组织才能进行CAM。可溶性已糖(葡萄糖和果糖)是绿色组织中夜间苹果酸累积的主要碳源。绿色组织G-1-P、G-6-P和F-6-P水平在夜间的初期上升,后期下降,昼间的头3h仍下降,3h后变化不明显。绿色组织中OAA和PEP水平也发生昼夜变化。在贮水组织中没有测到淀粉、蔗糖、OAA和PEP。除葡萄糖和果糖外,WSP中其它代谢物的含量都远低于绿色组织,而且WSP中所有代谢物都无明显的昼夜变化。     

外源葡萄糖、果糖和NO供体(SNP)对盐胁迫下水稻种子萌发的影响

单独采用一氧化氮(nitric oxide,NO)供体硝普钠(sodiumnitroprusside,SNP)、葡萄糖和果糖浸种均不同程度地提高盐胁迫下水稻种子早期发芽率和发芽指数,SNP预处理可以不同程度地提高果糖和葡萄糖的含量;进一步采用葡萄糖和果糖分别与SNP混合后浸种,发现葡萄糖与SNP处理对盐胁迫下水稻种子的萌发有正协同效应,而果糖和SNP的组合处理对盐胁迫下水稻种子的萌发可能受到SNP一定程度的负调控.此外,SNP对盐胁迫下幼苗生长的促进效应可以被葡萄糖和果糖处理所加强,其中葡萄糖的效应更明显.     

Molecular and functional characterization of a fructose specific transporter from the gray mold fungus Botrytis cinerea

In the gray mold fungus Botrytis cinerea, spore germination and plant infection are stimulated in the presence of nutrients, in particular sugars. Applied at micromolar concentrations, fructose is a more potent inducer of germination than glucose. To test whether preferred fructose uptake is responsible for this effect, and to study the mechanism of fructose transport in B. cinerea, a gene (frt1) encoding a fructose transporter was cloned. FRT1 is highly similar to recently identified fructose transporters of yeasts, but much less to other fungal hexose transporters characterized so far. By using a hexose uptake deficient yeast strain for expression, FRT1 was found to be a high affinity proton coupled symporter specific for fructose but not for glucose. B. cinerea frt1 disruption mutants were created and showed normal vegetative growth and plant infection, but a delay in fructose-induced germination when compared to wild-type. Sugar uptake experiments with both wild-type and mutant conidia showed a higher affinity for glucose than for fructose. Thus, we propose that the specific effect of fructose on germination is not due to transport but rather to an as yet unknown intracellular sensing.     

Role of glucose dehydrogenase in germination of Bacillus subtilis spores

Abstract A mutant of Bacillus subtilis has been isolated which is devoid of glucose dehydrogenase. This mutant is unable to germinate on a mix of glucose, fructose, asparagine, and KCl, which is a normal germination trigger for wild-type strains. Transfer of the genotype by transformation to isogenic strains confers the same properties on these transformed strains. These observations strongly implicate glucose dehydrogenase in germination.     

Ripe pollen carbohydrate changes in Trachycarpus fortunei: the effect of relative humidity

Pollen of the palm Trachycarpus fortunei was kept at 25°C and relative humidities (RH) of 20, 55 and 98%. Changes in viability, water content and carbohydrates were measured over 2–17 days. Water content remained almost constant at 20 and 50% RH and increased dramatically at 98%. Pollen viability and germination rate remained almost constant over 14 days at 20% RH and decreased to about 2% after 7–9 days at 55% and to even less at 98% RH. Although the three experimental conditions were constant, qualitative and quantitative variations in pollen carbohydrates were recorded, even after pollen had lost its viability. The quantities of mono-, di- and polysaccharides varied with the period of pollen storage at the various RH. The greatest changes in glucose, fructose and sucrose content were recorded at 55 and 98% RH. At these relative humidities, maximum glucose and fructose content and minimum sucrose content occurred at maximum water content. Starch was not present in mature pollen but appeared and peaked after 7–9 days of pollen storage at 55 and 98%. Appearance of starch coincided with an increase in pectin content. PAS-positive cytoplasmic polysaccharides showed an increasing trend at 20% RH. A relation was found between pollen viability, water content and monosaccharide content. Pollen viability and germination capacity remained high at 20% RH for 14 days. At this relative humidity, pollen water, glucose and fructose contents remained almost constant, while sucrose reached its maximum value. The fluctuations of more complex carbohydrates (starch, pectins and PAS-positive cytoplasmic polysaccharides) were less easy to interpret. Changes observed under experimental conditions could simulate processes occurring in nature during pollen presentation and dispersal.     

Evidence that glucose 6-phosphate is imported as the substrate for starch synthesis by the plastids of developing pea embryos

The aim of this work was to determine in what form carbon destined for starch synthesis crosses the membranes of plastids in developing pea (Pisum sativum L.) embryos. Plastids were isolated mechanically and incubated in the presence of ATP with the following ¹⁴C-labelled substrates: glucose, fructose, glucose 6-phosphate, glucose 1-phosphate, fructose 6-phosphate, fructose 1,6-bisphosphate, dihydroxyacetone phosphate. Glucose 6-phosphate was the only substrate that supported physiologically relevant rates of starch synthesis. Incorporation of label from glucose 6-phosphate into starch was dependent upon the integrity of the plastids and the presence of ATP. The rate of incorporation approached saturation at a glucose 6-phosphate concentration of less than 1 mM. It is argued that glucose 6-phosphate is likely to enter the plastid as the source of carbon for starch synthesis in vivo.Abbreviations ADPG PPase ADP-glucose pyrophosphorylase - DHAP dihydroxyacetone phosphate     

Photosynthetic carbohydrate metabolism in wheat (Triticum aestivum L.) leaves: optimization of methods for determination of fructose 2, 6-bisphosphate

The accurate measurement of fructose 2,6-bisphosphate from plants such as wheat is fraught with difficulty. Extraction and assay methods for fructose 2,6-bisphosphate that give near 100% recovery of the metabolite, and a linear response with volume have therefore been developed for extracts prepared from wheat leaves of different ages. Amounts of fructose 2,6-bisphosphate in different regions of leaves generally showed a positive correlation with chlorophyll content. Measurements of sucrose and starch in third leaves harvested at different times of the diurnal cycle demonstrated that sucrose is the major form in which photosynthate is stored in the leaf, but starch can account for up to about 30% of the stored carbohydrate. Virtually all of the carbohydrate accumulated as starch and sucrose during the day was degraded at night. Amounts of fructose 2,6-bisphosphate were generally lower in extracts prepared from leaves harvested in the light than in the dark. Additionally, there was no change in either the amount of fructose 2, 6-bisphosphate or the ratio of sucrose to starch in samples prepared from leaves harvested at different times of the day. These results are broadly consistent with a role for fructose 2,6-bisphosphate in the regulation of sucrose synthesis and the partitioning of carbohydrate between sucrose and starch in wheat leaves.     

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.     

Properties of α-glucan phosphorylase from pea chloroplasts

A partially purified preparation of α-glucan phosphorylase was obtained from chloroplasts of Pisum sativum by ion-exchange chromatography and gel filtration. The preparation, in which no other enzyme that metabolized starch or glucose 1 -phosphate could be detected, was characterized. The optimum for phosphorolysis was pH 7.2; at pH 8.0 the activity was reduced by 50%. The preparation showed normal hyperbolic kinetics with the substrates, and catalysed the formation of [¹⁴C]glucose 1-phosphate from ¹⁴C-labelled starch grains from pea chloroplasts. None of the following, generally at 5 and 10 mM, significantly altered the rate of phosphorolysis: glucose, fructose, sucrose, fructose 6-phosphate, fructose 1,6-bisphosphate, dihydroxyacetone phosphate, 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate, pyruvate, ATP, ADP, AMP, 6-phosphogluconate, 2-phosphoglycollate, Mg²⁺, dithiothreitol. However, phosphorolysis was inhibited by ADPglucose. Measurements of ADPglucose in leaves and in isolated chloroplasts showed that none could be detected in the dark and suggested that the concentration in the light was high enough to cause a modest inhibition of the phosphorylase. The control of the breakdown of chloroplast starch is discussed.     

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     

Copper Affects the Cotyledonary Carbohydrate Status During the Germination of Bean Seed

Seeds of bean (Phaseolus vulgaris L.) were germinated by soaking in distilled water or copper chloride solution. The relationships among copper excess treatment, germination rate, dry weight, sugar contents, and carbohydrase activities in cotyledon were investigated. Heavy metal stress provoked a diminution in germination rate and biomass mobilization, as compared with the control. A drastic disorder in soluble sugars export, especially glucose and fructose liberation, was also imposed after exposure to excess copper. This restricted the starch and sucrose breakdown in reserve tissue, as evidenced by the inhibition in the activities of α-amylase and invertase isoenzymes (soluble acid, soluble neutral, cell wall-bound acid).