Carbohydrate Depletion Research Articles

Antifungal activity in culture filtrates of the ectomycorrhizal fungus Pisolithus tinctorius

The ectomycorrhizal fungus Pisolithus tinctorius secreted a metabolite that lysed hypha and conidia and inhibited the germination of conidia in a range of phytopathogenic fungi. The optimum incubation period for the production of the metabolite by P. tinctorius in liquid culture was 42–56 days. Dilutions of the culture filtrate with fresh medium caused a gradient of inhibitory effects. For hyphal lysis the minimum ratio of culture filtrate to medium for complete growth inhibition was 5:1 for Rhizoctonia praticola and Truncatella hartigii and 3:1 for Sphaerosporella brunnea. At higher dilutions, the hyphae that formed were short celled and highly branched; many hyphae lysed. Conidial germination was completely inhibited at a ratio of 5:1 for both Fusarium solani and T. hartigii, 3:1 for a North American isolate of Brunchorstia pinea (NA), 1:1 for a European isolate of B. pinea (EU), and 1:3 for two strains of Cochliobolus sativus (0910, 0912). Conidial lysis was seen for T. hartigii at a ratio of 5:1 and at a ratio of 1:1 for B. pinea (EU) and C. sativus (0910). Characterization of the cell-free culture filtrate through the separate additions of D-glucose and an adsorbent, activated charcoal, showed that hyphal lysis and conidia germination inhibition did not result from a depletion of carbohydrates from the growth medium but from the presence of some substance adsorbed by charcoal. Key words: Pisolithus tinctorius, allelopathy, antifungal metabolite, hyphal lysis, mycorrhizosphere.

Photobioreactor culture of photosynthetic soybean cells

Photosynthetic suspension cultures of higher plants offer an alternative approach to biomass production, potentially yielding cellulosic material and protein on a continuous year-round basis. A bench-top hybrid photobioreactor was developed to study photomixotrophic and photoautotrophic growth of Glycine max as a model system. Maximum biomass doubling times for photomixotrophic and photoautotrophic growth were 1.87 and 3.92 d, respectively. The presence of exogenous sugars resulted in photomixotrophic growth, reduced chlorophyll levels, and a reduction in photosynthetically-evolved oxygen. Depletion of carbohydrates from the medium coincided with the beginning of stationary phase and an increase in oxygen evolution by the cells. A second growth phase, prolonging cell viability, could be initiated by increasing the carbon dioxide from 2 to 5%, just before the onset of stationary phase. Biomass from bioreactor cultured cells proved resistant to enzymatic attack without pretreatment. Composition of the biomass was 7.8% lignin, 20.7% α-cellulose, 23% hemicellulose, 5.5% starch, 14.5% protein and 6.5% nucleic acids.

Effects on mitochondrial metabolism in livers of guinea pigs after a single or repeated injection of As2O3.

Differences in the metabolite pattern were observed in previous experiments in guinea pig livers after a single injection or prolonged (5 days) treatment with AS2O3 (Reichl et al. 1988). To elucidate the underlying mechanism the effect of As2O3 on liver metabolism was therefore investigated. Male guinea pigs received either a single dose (s.d.) of As2O3 10 mg x kg-1 s.c. or repeated doses (r.d.) of 2.5 mg x kg-1b.i.d. on 5 consecutive days. One hour after the s.d. or 1 h and 16 h after the last injection in the r.d. groups the animals were sacrificed in anaesthesia. The livers were removed by freeze clamping for the determination of various metabolites. In the s.d. group a significant decrease in hydroxybutyrate, acetylCoA, adenosinemonophosphate and in the ratio of hydroxybutyrate/acetoacetate and an increase in pyruvate, citrate, malate, and adenosinetriphosphate were observed. A significant decrease in glycogen, pyruvate, alpha-ketoglutarate, acetylCoA, and acetoacetate and a significant increase in malate and in the ratios of lactate/pyruvate and hydroxybutyrate/acetoacetate were observed in the r.d.1-h group. In the r.d.16-h group a significant decrease in glycogen, pyruvate, lactate, and adenosinemonophosphate was found, but the values tended towards control values. The data are consistent with mechanisms of As2O3 toxicity in other species as PDH inhibition with consecutive citric acid cycle and gluconeogenesis inhibition and excessive carbohydrate depletion.

Effect of deglycosylation of N-linked sugar chains on glucose oxidase from Aspergillus niger

Endo-beta-N-acetylglucosaminidase from Flavobacterium sp. released about 30% of the N-linked sugar chains from the glucose oxidase of Aspergillus niger. To elucidate the role of the carbohydrate moiety, the enzymatic properties of native and carbohydrate-depleted glucose oxidases were compared. It was found that their catalytic activities and thermal and pH stabilities were identical. However, the carbohydrate-depleted glucose oxidase was more rapidly precipitated by the addition of trichloroacetic acid and ammonium sulfate than the native enzyme. These results show that the N-linked sugar chains of the glucose oxidase contributed to the high solubility of the enzyme in water.

Effects of Altered Carbohydrate Availability on Whole-Plant Assimilation of 15NO3−

An experiment was conducted to investigate the relative changes in NO(3) (-) assimilatory processes which occurred in response to decreasing carbohydrate availability. Young tobacco plants (Nicotiana tabacum [L.], cv NC 2326) growing in solution culture were exposed to 1.0 millimolar (15)NO(3) (-) for 6 hour intervals during a normal 12 hour light period and a subsequent period of darkness lasting 42 hours. Uptake of (15)NO(3) (-) decreased to 71 to 83% of the uptake rate in the light during the initial 18 hours of darkness; uptake then decreased sharply over the next 12 hours of darkness to 11 to 17% of the light rate, coincident with depletion of tissue carbohydrate reserves and a marked decline in root respiration. Changes also occurred in endogenous (15)NO(3) (-) assimilation processes, which were distinctly different than those in (15)NO(3) (-) uptake. During the extended dark period, translocation of absorbed (15)N out of the root to the shoot varied rhythmically. The adjustments were independent of (15)NO(3) (-) uptake rate and carbohydrate status, but were reciprocally related to rhythmic adjustments in stomatal resistance and, presumably, water movement through the root system. Whole plant reduction of (15)NO(3) (-) always was limited more than uptake. The assimilation of (15)N into insoluble reduced-N in roots remained a constant proportion of uptake throughout, while assimilation in the shoot declined markedly in the first 18 hours of darkness before stabilizing at a low level. The plants clearly retained a capacity for (15)NO(3) (-) reduction and synthesis of insoluble reduced-(15)N even when (15)NO(3) (-) uptake was severely restricted and minimal carbohydrate reserves remained in the tissue.

Mechanisms of Starvation Tolerance in Pearl Millet

The response of pearl millet (Pennisetum glaucum [L.]) seedlings to prolonged starvation was investigated at the biochemical and ultrastructural level. After 2 days of darkness the bulk of the seedling carbohydrate reserves were depleted. After 8 days in the dark the respiratory rate had declined to less than 50% of its initial value and the plants had lost half of their total protein content. Unlike the situation with carbohydrate depletion, protein loss was restricted to specific organs. The secondary leaf and stem (including the apical meristem) showed little or no protein loss during this period. In the primary leaf, seed, and roots, protein loss was substantial. In spite of the high rate of protein degradation in the primary leaf and roots, these organs showed no ultrastructural changes suggestive of tissue, cellular, or subcellular degradation. In addition, ribulose bisphosphate carboxylase was not preferentially degraded during starvation and only a small decline in chlorophyll content was observed after 8 days in the dark. During the period from 8 to 14 days, cell death started at the tip of the primary leaf and gradually spread downward. Both shoot and root meristems remained alive up to 14 days. Consequently, the eventual death of the plant was due to the loss of the carbohydrate-producing regions rather than the meristems. We suggest that these results provide an explanation for the high degree of starvation tolerance exhibited by pearl millet.

Uptake and Assimilation of NO3− and NH4+ by Nitrogen-Deficient Perennial Ryegrass Turf

Assimilation of NO(3) (-) and NH(4) (+) by perennial ryegrass (Lolium perenne L.) turf, previously deprived of N for 7 days, was examined. Nitrogen uptake rate was increased up to four- to five-fold for both forms of N by N-deprivation as compared to N-sufficient controls, with the deficiency-enhanced N absorption persisting through a 48 hour uptake period. Nitrate, but not NH(4) (+), accumulated in the roots and to a lesser degree in shoots. By 48 hours, 53% of the absorbed NO(3) (-) had been reduced, whereas 97% of the NH(4) (+) had been assimilated. During the early stages (0 to 8 hours) of NO(3) (-) uptake by N-deficient turf, reduction occurred primarily in the roots. Between 8 and 16 hours, however, the site of reduction shifted to the shoots. Nitrogen form did not affect partitioning of the absorbed N between roots (40%) and shoots (60%) but did affect growth. Compared to NO(3) (-), NH(4) (+) uptake inhibited root, but not shoot, growth. Total soluble carbohydrates decreased in both roots and shoots during the uptake period, principally the result of fructan metabolism. Ammonium uptake resulted in greater total depletion of soluble carbohydrates in the root compared to NO(3) (-) uptake. The data indicate that N assimilation by ryegrass turf utilizes stored sugars but is also dependent on current photosynthate.

Fungal degradation of polyvinyl acetate

Certain Aspergillus and Penicillium strains isolated from soil grow well and degrade a commercial sample of polyvinyl acetate (PVA, 4.5 g liter −1) when it is used as the only carbon source. These strains showed an increase in dry weight after 11 days of incubation, along with a depletion of carbohydrates, protein, and deoxyribonucleic acid. This was interpreted as an active turnover of the above metabolites during the degradation. This effect was greatly enhanced by equilibrating the carbon:nitrogen ratio by addition of yeast extract in the original culture. The increase in esterase activity and the loss of viscosity were also considered evidence of the fungal degradation. Isolation of the enzyme was attempted, but unsuccessful.

Histological and histochemical observations on the digestive gland ofMelanoides tuberculatus (Gastropoda) infected with certain larval trematodes and focus on their mode of nutrition

Histological and histochemical observations were made on infected and uninfected digestive glands of snails,Melanoides tuberculatus. Infected gland either with sporocysts ofCercaria diglandulata (Xiphidio) or with rediae ofCercaria martini (Monostome) revealed basically two types of histopathological abnormalities (damages), mechanical (lesion 1) and physiological (lesion 2). Depletion of carbohydrates, lipids and proteins as well as increased activities of phosphatases, lipase, non-specific esterase and glucose-6-phosphatase were also reflected by infected digestive gland. Alterations either histological or histochemical in infected glands are associated with the type and size of trematode larvae and degree of parasitemea and these were greater in glands infected with rediae than in sporocysts. Besides pathogenesis, the present study also focusses on the mode of nutrition in certain trematode larvae.

Limiting carbohydrate stores: alleviating the problem in the marathon runner, a hibernating lizard, and the neonate brain

The marathon runner is always potentially short of carbohydrate, and the best runners use more lipid and thus conserve carbohydrate. It turns out that training enables more effective use of intramuscular lipid, thus bypassing the problem of transporting lipid fuels across cell membranes. The bobtail lizard (Tiliqua rugosa) hibernates in winter and relies on "on board" fuel supplies during this period. One way that the bobtail conserves carbohydrate is by having a dearth of those tisses that rely on carbohydrate for fuel and consequently produce lactate. This strategy is reflected in the low resting lactate turnover of the bobtail, which is only 0.1% of that of a mammal. The neonate rat brain encounters a profound hypoglycaemia in the first 3 h of life. It counters this problem by using lactate for the first 1–2 h, and ketones for the next 2 h. These three situations demonstrate (i) that carbohydrate depletion as a problem is widespread in the animal kingdom, (ii) that the solutions to the problem involve many biological systems, and (iii) that solutions are more constrained within than between species.

Carbohydrate ingestion and muscle glycogen depletion during marathon and ultramarathon racing.

Two studies were undertaken to characterize the effects of carbohydrate ingestion on fuel/hormone response to exercise and muscle glycogen utilization during prolonged competitive exercise. In study 1, eighteen subjects were divided into three groups, matched for maximum oxygen consumption (VO2max) and blood lactate turnpoint. All subjects underwent a 3-day carbohydrate (CHO) depletion phase, followed by 3 days of CHO loading (500-600 g.day-1). During the race, the groups drank either 2% glucose (G), 8% glucose polymer (GP), or 8% fructose (F). Muscle biopsies were performed before and after the race and venous blood was sampled before and at regular intervals during the race. In study 2, eighteen subjects divided into 2 matched groups ingested either a 4% G or 10% GP solution during a 56 km race. Despite significantly greater CHO ingestion by GP and F in study 1 and by GP in study 2, blood glucose, free fatty acids and insulin concentrations, muscle glycogen utilization and running performance were not different between groups. These studies show (i) that hypoglycaemia is uncommon in athletes competing in races of up to 56 km provided they CHO-load before and ingest a minimum of 10 g CHO.h-1 during competition; (ii) that neither the amount (10 g vs 40 g.h-1) nor the type of carbohydrate (G vs GP vs F) has any effect on the extent of muscle glycogen depletion or running performance in matched subjects racing over distances up to 56 km.

Role of Carbohydrates in Diurnal Chilling Sensitivity of Tomato Seedlings

Tomato seedlings (Lycopersicon esculentum Mill.) chilled starting at different times during the light/dark cycle were most chilling-sensitive at the end of the dark period (AI King, MS Reid, BD Patterson 1982 Plant Physiol 70: 211-214). Low-temperature tolerance was regained with as little as 10 minutes of light exposure. Low light intensities were less effective than high light intensities in reducing sensitivity, and the length of exposure to light directly influenced sensitivity. Seedlings kept at low night temperatures prior to chilling were also less injured following chilling. Light also restored chilling tolerance to seedlings whose roots were removed. Supplying cut shoots with sucrose, glucose, or fructose reduced chilling sensitivity and largely eliminated the diurnal difference in sensitivity. Endogenous carbohydrate content was correlated with changes in chilling sensitivity; starch and sugar content fell markedly during the dark period. Increased concentrations of sugars were detected 15 minutes after the start of the light period. This evidence all suggests that changes in chilling sensitivity over the diurnal period are regulated by the light cycle. It also suggests that increased sensitivity at the end of the dark period could be due to carbohydrate depletion, and that chilling tolerance following light exposure is likely due to carbohydrate accumulation or closely related events.

Trends in Carbohydrate Depletion, Respiratory Carbon Loss, and Assimilate Export from Soybean Leaves at Night

To evaluate assimilate export from soybean (Glycine max [L.] Merrill) leaves at night, rates of respiratory CO(2) loss, specific leaf weight loss, starch mobilization, and changes in sucrose concentration were measured during a 10-hour dark period in leaves of pod-bearing ;Amsoy 71' and ;Wells II' plants in a controlled environment. Lateral leaflets were removed at various times between 2200 hours (beginning dark period) and 0800 hours (ending dark period) for dry weight determination and carbohydrate analyses. Respiratory CO(2) loss was measured throughout the 10-hour dark period. Rate of export was estimated from the rate of loss in specific leaf weight and rate of CO(2) efflux. Rate of assimilate export was not constant. Rate of export was relatively low during the beginning of the dark period, peaked during the middle of the dark period, and then decreased to near zero by the end of darkness. Rate of assimilate export was associated with rate of starch mobilization and amount of starch reserves available for export. Leaves of Amsoy 71 had a higher maximum export rate in conjunction with a greater total change in starch concentration than did leaves of Wells II. Sucrose concentration rapidly declined during the first hour of darkness and then remained constant throughout the rest of the night in leaves of both cultivars. Rate of assimilate export was not associated with leaf sucrose concentration.

The mechanism of folding of pancreatic ribonucleases is independent of the presence of covalently linked carbohydrate.

The role of asparagine-linked oligosaccharides for the mechanism of protein folding was investigated. We compared the stability and folding kinetics for two sets of pancreatic ribonucleases (RNases) with identical amino acid sequences and differences in glycosylation. First the folding of RNases A (carbohydrate free) and B (a single N-linked oligosaccharide) from bovine pancreas was investigated. The kinetics of refolding were identical under a wide range of conditions. The rate of unfolding by guanidinium chloride was decreased in RNase B. In further experiments the folding of porcine RNase (three carbohydrate chains at Asn-21, -34, and -76) was compared with the corresponding data for the deglycosylated protein. Even for this RNase with almost 40% carbohydrate content the mechanism of refolding is independent of glycosylation. Although the folding mechanism is conserved, the rates of individual steps in folding are decreased about 2-fold upon deglycosylation. We interpret this to originate from a slight destabilization of folding intermediates by carbohydrate depletion. In control experiments with nonglycosylated bovine RNase A it was ascertained that treatment with HF (as used for deglycosylation) did not affect the folding kinetics. The in vitro folding mechanism of glycosylated RNases apparently does not depend on the presence of N-linked oligosaccharide chains. The information for the folding of glycoproteins is contained exclusively in the protein moiety, i.e. in the amino acid sequence. Carbohydrate chains are attached at chain positions which remain solvent exposed. This ensures that the presence of oligosaccharides does not interfere with correct folding of the polypeptide chain.

What Determines Food Intake? The Ischymetric Theory

Hunger is elicited by depletion of nutrients, but what specific signals cause food intake? Recent data suggest that the signal comes not from depletion of carbohydrates or other major nutrients but from overall decreased cellular power production. And what causes satiation, which occurs largely before ingested nutrients can cross the intestinal barrier and replete the inner supply? Metabolic hormones such as glucagon and insulin are released and induce mobilization of endogenous reserves, thus inhibiting further ingestion of food.

The effects of age on substrate depletion and hormonal responses during submaximal exercise in hamsters

Senescent hamsters display a marked reduction in volume of voluntary running. The purpose of this study was to determine whether age differences exist in the pattern of fuel utilization during submaximal exercise, which may account for the reduction in voluntary running. Further, we determined the effects of age on muscle oxidative capacity to assess its relationship to endurance performance in senescent hamsters Depletion of carbohydrate and lipid content of skeletal muscle and liver, and changes in blood concentration of various hormones and substrates during one hour of exercise at 60 percent of VO 2 max served to assess age effects on utilization of metabolic substrates. Exercise produced equivalent depletion of muscle glycogen and similar rise in plasma free fatty acids in young and old hamsters. No exercise effects on skeletal muscle triglyceride concentration or on plasma glycerol, glucagon or catecholamine concentrations were noted. With palmitoyl carnitine as substrate (but not with pyruvate) State 3 respiration of cardiac and skeletal muscle homogenates was lower in old compared to young hamsters. Although old hamsters have a reduced capacity to oxidize lipids in vitro, few age differences in fuel use are evident in vivo during submaximal exercise. Thus, these minor age differences in substrate utilization do not likely account for the substantial reduction in the levels of spontaneous running in senescent hamsters.

Marathon fatigue: the role of plasma fatty acids, muscle glycogen and blood glucose.

The role of carbohydrate depletion in marathon fatigue was examined in 6 marathon runs. Four of the runs were potentially 'fast-time' marathons and culminated in fatigue. The utilization of carbohydrate, lipid and protein, and plasma concentrations of free fatty acids (FFA), glucose and lactate were measured at intervals throughout the runs. The contribution from protein to energy output was low (1-2%). The utilization of lipid was dependent upon plasma concentrations of FFA, which rose throughout the run. The utilization of carbohydrate mirrored that of FFA and thus fell throughout the run. Fatigue was characterized by a drop in running speed, a drop in carbohydrate utilization, an unchanging FFA utilization and a fall in blood glucose. The fall in blood glucose was not seen in the non-fatigued runners. These results are consistent with carbohydrate depletion being the cause of fatigue. The implications of these data are that lipid is the preferred fuel, but is rate-limiting, and that carbohydrate depletion, even though it causes fatigue, ensures an optimal-time marathon.

Carbon and nitrogen allocation patterns of Douglas-fir seedlings fertilized with nitrogen in autumn. II. Field performance

October-fertilized and unfertilized 2-0 Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings were outplanted the following February. Half of each planting block was seeded with grass to induce water stress during the typical summer drought. Sucrose was applied to soil around each seedling to limit availability of nitrogen to tree roots. Fertilized seedlings broke bud 9–10 days earlier, produced more shoot growth, and, as shown in later harvests, had higher relative growth rates than unfertilized seedlings. However, initial differences in growth response were due primarily to the earlier budbreak. Seedlings growing with grass had predawn water potentials of −1.5 MPa by early August; by September 3, unfertilized seedlings growing with grass were significantly more stressed than any others. Although free amino acid and total nitrogen concentrations were higher in fertilized than unfertilized seedlings when planted, they became equal by the end of one growing season. However, fertilized seedlings contained more free amino acids and nitrogen because of their greater size. Grass competition affected both seedling nitrogen and carbohydrate chemistry. After one growing season, fertilized seedlings had greater height increment, shoot growth, leaf area, relative growth rate, and production per unit nitrogen. Although autumn fertilization benefited these Douglas-fir seedlings, negative effects could result from carbohydrate depletion because of increased respiration or from frost damage because of earlier budbreak.

Hemolymph carbohydrate and lipid mobilization in Locusta migratoria in relation to the progress of poisoning following bioresmethrin treatment

Effects of bioresmethrin, a pyrethroid insecticide, on the mobilization of metabolic reserves in the hemolymph of Locusta migratoria were studied. Bioresmethrin treatment of intact locusts caused depletion of hemolymph carbohydrate (hypoglycemia) and elevation in blood lipid (hyperlipemia). The mobilization of these metabolic reserves was found to be closely related to the poisoning syndrome of this insecticide. Bioresmethrin-induced hyperlipemia was not detected in neck-ligated locusts, whereas hypoglycemia was still observed. The results of this study suggest that bioresmethrin-induced elevation in hemolymph lipid is due to the release of hyperlipemic hormone(s). The depletion of hemolymph carbohydrate, on the other hand, may be due to their increased utilization in response to the hyperactivity caused by the insecticide treatment.

Optimal use of fluids of varying formulations to minimise exercise-induced disturbances in homeostasis.

The rationale underlying the development of various formulations of beverages for consumption before, during, and/or after physical exercise is that such formulations should minimise some of the disturbances in physiological homeostasis that occur during exercise and thereby prevent injury and/or enhance performance. Exercise- and dehydration-induced increases in core temperature, body fluid osmolality, heart rate, losses of plasma and other body fluid volumes, and carbohydrate depletion are probably the most important homeostatic disturbances that can be ameliorated by fluid consumption. With the exception of athletes subject to hyponatraemia after consumption of ordinary water during prolonged activity, changes in electrolyte concentrations in the body fluids of most athletes do not justify the inclusion of electrolytes in fluid replacement beverages to be consumed during exercise. However, small amounts of sodium added to water does speed gastric emptying and fluid absorption from the intestine. Recent evidence suggests that a precompetition meal high in easily digested carbohydrates should be consumed not later than 5 to 6 hours before competition. There is little published research on the optimal composition of this meal. Water ingestion 30 to 60 minutes before exercise seems to be of benefit to temperature regulation and cardiovascular homeostasis if the exercise is of moderate intensity (50 to 65% VO2max), but probably has little effect at the higher intensities of athletic performance. There is no systematic evidence to support the inclusion of calcium or sodium chloride in drinks consumed an hour or 2 before exercise. Furthermore, if glucose solutions are fed 15 to 45 minutes before prolonged exercise, they will probably cause a fall in blood glucose during exercise and may adversely affect performance. These adverse effects are not present when fructose is consumed before exercise. Contrary to the adverse effects of glucose feedings 15 to 60 minutes before exercise, the consumption of 18 to 50% solutions of glucose or glucose polymers 5 minutes before prolonged exercise seems to have potential for improving endurance performance. Similarly, the inclusion of caffeine in beverages consumed 60 minutes before prolonged exercise improves athletic performance for many subjects. Others may be hypersensitive to the effects of caffeine and are adversely affected by its use. For exercise leading to exhaustion in less than 30 minutes, neither caffeine nor carbohydrate ingestion is effective in minimising homeostatic perturbations or improving exercise performance.(ABSTRACT TRUNCATED AT 400 WORDS)