Kegg Pathway: Starch and sucrose metabolism

Planta. 2009 Nov 8;
Aleman L, Ortega JL, Martinez-Grimes M, Seger M, Holguin FO, Uribe DJ, Garcia-Ibilcieta D, Sengupta-Gopalan C

sucrose phosphate synthase (SPS) catalyzes the first step in the synthesis of sucrose in photosynthetic tissues. We characterized the expression of three different isoforms of SPS belonging to two different SPS gene families in alfalfa (Medicago sativa L.), a previously identified SPS (MsSPSA) and two novel isoforms belonging to class B (MsSPSB and MsSPSB3). While MsSPSA showed nodule-enhanced expression, both MsSPSB genes exhibited leaf-enhanced expression. Alfalfa leaf and nodule SPS enzymes showed differences in chromatographic and electrophoretic migration and differences in V (max) and allosteric regulation. The root nodules in legume plants are a strong sink for photosynthates with its need for ATP, reducing power and carbon skeletons for dinitrogen fixation and ammonia assimilation. The expression of genes encoding SPS and other key enzymes in sucrose metabolism, sucrose phosphate phosphatase and sucrose synthase, was analyzed in the leaves and nodules of plants inoculated with Sinorhizobium meliloti. Based on the expression pattern of these genes, the properties of the SPS isoforms and the concentration of Starch and soluble sugars in nodules induced by a wild type and a nitrogen fixation deficient strain, we propose that SPS has an important role in the control of carbon flux into different metabolic pathways in the symbiotic nodules.

Plant J. 2009 Oct 20;
Riebeseel E, Häusler RE, Radchuk R, Meitzel T, Hajirezaei MR, Neil Emery RJ, Küster H, Nunes-Nesi A, Fernie AR, Weschke W, Weber H

Summary Heterotrophic plastids of seeds perform many biosynthetic reactions. Understanding their function in crop plants is crucial for seed production. Physiological functions depend on the uptake of precursors by a range of different metabolite translocators. The 2-oxoglutarate/malate translocator gene (PsOMT), which is highly expressed during pea embryo maturation, has an important role during seed storage. PsOMT-functions have been studied by antisense repression in maturing pea embryos, which reduced mRNA-levels and transport rates of 2-oxoglutarate and malate by 50 to 70%. Combined metabolite and transcript profiling revealed that OMT-repression affects conversion of carbohydrates from sucrose into amino acids and proteins, decreases seed weight and delays maturation. OMT-repressed pea embryos have increased levels of organic acids, ammonia and higher ratios of Asn:Asp and Gln:Glu. Decreased amounts of most other amino acids indicate reduced usage of organic acids and ammonia for amino acid biosynthesis in plastids, possibly caused by substrate limitation of the plastidial glutamine synthetase/glutamine:2-oxoglutarate aminotransferase cycle. Expression of storage proteins is delayed and mature seeds have reduced protein contents. Downregulated gene expression of Starch biosynthesis and plastidial Glc-6-P transport in asOMT-embryos reveals that decreased 2-oxoglutarate/malate transport capacity affects other pathways of central carbon metabolism. Gene expression analysis related to plastid physiology revealed that OMT-repression delays differentiation of storage plastids thereby maintaining gene expression associated to green chloroplasts. We conclude that OMT is important for protein-storing crop seeds and necessary for amino acid biosynthesis in pea seeds. In addition, carbon supply as mediated by OMT controls plastid differentiation during seed maturation.

Ann Bot (Lond). 2009 Sep 29;
Ramel F, Sulmon C, Gouesbet G, Couée I

Background Soluble sugars are involved in responses to stress, and act as signalling molecules that activate specific or hormone cross-talk transduction pathways. Thus, exogenous sucrose treatment efficiently induces tolerance to the herbicide atrazine in Arabidopsis thaliana plantlets, at least partially through large-scale modifications of expression of stress-related genes. Methods Availability of sugars in planta for stress responses is likely to depend on complex dynamics of soluble sugar accumulation, sucrose-Starch partition and organ allocation. The question of potential relationships between endogenous sugar levels and stress responses to atrazine treatment was investigated through analysis of natural genetic accessions of A. thaliana. Parallel quantitative and statistical analysis of biochemical parameters and of stress-sensitive physiological traits was carried out on a set of 11 accessions. Key Results Important natural variation was found between accessions of A. thaliana in pre-stress shoot endogenous sugar levels and responses of plantlets to subsequent atrazine stress. Moreover, consistent trends and statistically significant correlations were detected between specific endogenous sugar parameters, such as the pre-stress end of day sucrose level in shoots, and physiological markers of atrazine tolerance. Conclusions These significant relationships between endogenous carbohydrate metabolism and stress response therefore point to an important integration of carbon nutritional status and induction of stress tolerance in plants. The specific correlation between pre-stress sucrose level and greater atrazine tolerance may reflect adaptive mechanisms that link sucrose accumulation, photosynthesis-related stress and sucrose induction of stress defences.

J Exp Bot. 2009; 60(15): 4301-14
Le Bot J, Bénard C, Robin C, Bourgaud F, Adamowicz S

Plants allocate internal resources to fulfil essential, yet possibly conflicting, demands such as defence or growth, as hypothesized by the 'growth-differentiation balance theory' (GDB). This trade-off was examined in young tomato plants grown for 25 d using the nutrient film technique with seven nitrate concentrations ([NO(3)]). The modification of primary (growth-related: organic acids, carbohydrates) and secondary (defence-related: phenolics) metabolite concentrations in leaves was assessed. Then a simple model was devised to simulate the trade-off between growth and secondary metabolism in response to N nutrition. N affected growth and metabolite concentrations in the leaves. Dry biomass, leaf area, and concentrations of nitrate and organic acid (malic, citric) increased with rising [NO(3)], up to a threshold, above which they remained constant. Starch, sucrose, and organic N concentrations were invariant with [NO(3)]. Glucose, fructose, and phenolic (chlorogenic acid, rutin, and kaempferol-rutinoside) concentrations were highest at lowest [NO(3)]. They declined progressively with rising [NO(3)] until a threshold, above which they remained constant. Model predictions are in phase with experimental phenolic concentration data although the simulated metabolic rates differ from the GDBH proposals depicted in the literature. From the model output it is shown that a careful definition of the C reserve compounds is required.

J Exp Bot. 2009; 60(15): 4235-48
Gandin A, Lapointe L, Dizengremel P

Mechanisms that allow plants to cope with a recurrent surplus of carbon in conditions of imbalance between source and sink activity has not received much attention. The response of sink growth and metabolism to the modulation of source activity was investigated using elevated CO(2) and elevated O(3) growth conditions in Erythronium americanum. Sink activity was monitored via slice and mitochondrial respiratory rates, sucrose hydrolysis activity, carbohydrates, and biomass accumulation throughout the growth season, while source activity was monitored via gas exchanges, rubisco and phosphoenolpyruvate carboxylase activities, carbohydrates, and respiratory rates. Elevated CO(2) increased the net photosynthetic rate by increasing substrate availability for rubisco. Elevated O(3) decreased the net photosynthetic rate mainly through a reduction in rubisco activity. Despite this modulation of the source activity, neither plant growth nor Starch accumulation were affected by the treatments. sucrose synthase activity was higher in the sink under elevated CO(2) and lower under elevated O(3), thereby modulating the pool of glycolytic intermediates. The alternative respiratory pathway was similarly modulated in the sink, as seen with both the activity and capacity of the pathway, as well as with the alternative oxidase abundance. In this sink-limited species, the alternative respiratory pathway appears to balance carbon availability with sink capacity, thereby avoiding early feedback-inhibition of photosynthesis in conditions of excess carbon availability.

Horm Metab Res. 2009 Aug 21;
Holub I, Gostner A, Hessdörfer S, Theis S, Bender G, Willinger B, Schauber J, Melcher R, Allolio B, Scheppach W

The polyol isomalt (Palatinit ((R))) is a very low glycaemic sugar replacer. The effect of food supplemented with isomalt instead of higher glycaemic ingredients like sucrose and/or Starch hydrolysates on metabolic control in patients with type 2 diabetes was examined in this open study. Thirty-three patients with type 2 diabetes received a diet with foods containing 30 g/d isomalt instead of higher-glycaemic carbohydrates for 12 weeks. Metformin and/or thiazolidindiones were the only concomitant oral antidiabetics allowed during the study. Otherwise, the participants maintained their usual diet during the test phase, but were instructed to refrain from additional sweetened foods. Before start, after 6 weeks and 12 weeks (completion of the study), blood samples were taken and analysed for clinical routine parameters, metabolic, and risk markers. Thirty-one patients completed the study. The test diet was well accepted and tolerated. After 12 weeks, significant reductions were observed for: glycosylated haemoglobin, fructosamine, fasting blood glucose, insulin, proinsulin, C-peptide, insulin resistance (HOMA-IR), and oxidised LDL (an atherosclerosis risk factor). In addition, significant lower nonesterified fatty acid concentrations were found in female participants. Routine blood measurements and blood lipids remained unchanged. The substitution of glycaemic ingredients by isomalt and the consequent on reduction of the glycaemic load within otherwise unchanged diet was accompanied by significant improvement in the metabolic control of diabetes. The present study is in agreement with findings of previous reported studies in human subjects demonstrating beneficial effects of low glycaemic diets on glucose metabolism in patients with diabetes mellitus type 2.

Mol Biol Rep. 2009 Aug 13;
Li G, Peng F, Zhang L, Shi X, Wang Z

sucrose non-fermenting-1-related protein kinase-1 (SnRK1) plays an important role in metabolic regulation in plant. To understand the molecular mechanism of amino acids and carbohydrate metabolism in Malus hupehensis Rehd. var. pinyiensis Jiang (Pingyi Tiancha, PYTC), a full-length cDNA clone encoding homologue of SnRK1 was isolated from PYTC by Rapid Amplification of cDNA Ends (RACE). The clone, designated as MhSnRK1, contains 2063 nucleotides with an open reading frame of 1548 nucleotides. The deduced 515 amino acids showed high identities with other plant SnRK1 genes. Quantitative real-time PCR analysis revealed this gene was expressed in roots, stems and leaves. Exposing seedlings to nitrate caused and initial decrease in expression of the MhSnRK1 gene in roots, leaves and stems in short term. Ectopic expression of MhSnRK1 in tomato mainly resulted in higher Starch content in leaf and red-ripening fruit than wild-type plants. This result supports the hypothesis that overexpression of SnRK1 causes the accumulation of Starch in plant cells. All the results suggest that MhSnRK1 may play important roles in carbohydrate and amino acid metabolisms.

Phytochemistry. 2009 Jun; 70(9): 1117-22
Troncoso-Ponce MA, Kruger NJ, Ratcliffe G, Garcés R, Martínez-Force E

Unlike other oilseeds (e.g. Arabidopsis), developing sunflower seeds do not accumulate a lot of Starch and they rely on the sucrose that comes from the mother plant to synthesise lipid precursors. Between 10 and 25 days after flowering (DAF), when sunflower seeds form and complete the main period of storage lipid synthesis, the sucrose content of seeds is relatively constant. By contrast, the glucose and fructose content falls from day 20 after flowering and it is always lower than that of sucrose, with glucose being the minor sugar at the end of the seed formation. By studying the apparent kinetic parameters and the activity of glycolytic enzymes in vitro, it is evident that all the components of the glycolytic pathway are present in the crude seed extract. However, in isolated plastids important enzymatic activities are missing, such as the glyceraldehyde-3-phosphate dehydrogenase, involved in the conversion of glyceraldehyde 3-phosphate into 1,3-biphospho-glycerate, or the enolase that converts 2-phosphoglycerate into phosphoenolpyruvate. Hence, phosphoenolpyruvate or one of its derivatives, like pyruvate and malate from the cytosol, may be the primary carbon sources for lipid biosynthesis. Accordingly, the glucose-6-P imported into the plastid is likely to be used in the pentose phosphate pathway to produce the reducing power for lipid biosynthesis in the form of NADPH. Data from crude seed extracts indicate that enolase activity increased during seed formation, from 16 days after flowering, and that this activity was well correlated with the period of storage lipid synthesis. In addition, while the presence of some glycolytic enzymes increased during lipid synthesis, others decreased, remained constant, or displayed irregular temporal behaviour.

Nutr Res. 2009 Jun; 29(6): 383-90
Sands AL, Leidy HJ, Hamaker BR, Maguire P, Campbell WW

Limited research in humans suggests that slowly digestible Starch may blunt the postprandial increase and subsequent decline of plasma glucose and insulin concentrations, leading to prolonged energy availability and satiety, compared to more rapidly digestible Starch. This study examined the postprandial metabolic and appetitive responses of waxy maize Starch (WM), a slow-digestible Starch. It was hypothesized that the waxy maize treatment would result in a blunted and more sustained glucose and insulin response, as well as energy expenditure and appetitive responses. Twelve subjects (6 men and 6 women) (age, 23 +/- 1 years; body mass index, 22.2 +/- 0.7 kg/m(2); insulin sensitivity [homeostatic model assessment], 16% +/- 2%; physical activity, 556 +/- 120 min/wk) consumed, on separate days, 50 g of available carbohydrate as WM, a maltodextrin-sucrose mixture (MS), or white bread (control). Postprandial plasma glucose and insulin, energy expenditure, and appetite (hunger, fullness, desire to eat) were measured over 4 hours. Compared to control, the 4-hour glucose response was not different for MS and WM, and the 4-hour insulin response was higher for MS (P < .005) and lower for WM (P < .05). Compared to MS, WM led to lower 4-hour glucose and insulin responses (P < .001). These differences were driven by blunted glucose and insulin responses during the first hour for WM. Postprandial energy expenditure and appetite were not different among treatments. These results support that WM provides sustained glucose availability in young, insulin-sensitive adults.

Plant Cell Physiol. 2009 Sep; 50(9): 1651-62
Baroja-Fernández E, Muñoz FJ, Montero M, Etxeberria E, Sesma MT, Ovecka M, Bahaji A, Ezquer I, Li J, Prat S, Pozueta-Romero J

sucrose synthase (SuSy) is a highly regulated cytosolic enzyme that catalyzes the conversion of sucrose and a nucleoside diphosphate into the corresponding nucleoside diphosphate glucose and fructose. To determine the impact of SuSy activity in Starch metabolism and yield in potato (Solanum tuberosum L.) tubers we measured sugar levels and enzyme activities in tubers of SuSy-overexpressing potato plants grown in greenhouse and open field conditions. We also transcriptionally characterized tubers of SuSy-overexpressing and -antisensed potato plants. SuSy-overexpressing tubers exhibited a substantial increase in Starch, UDPglucose and ADPglucose content when compared with controls. Tuber dry weight, Starch content per plant and total yield of SuSy-overexpressing tubers increased significantly over those of control plants. In contrast, activities of enzymes directly involved in Starch metabolism in SuSy-overexpressing tubers were normal when compared with controls. Transcriptomic analyses using POCI arrays and the MapMan software revealed that changes in SuSy activity affect the expression of genes involved in multiple biological processes, but not that of genes directly involved in Starch metabolism. These analyses also revealed a reverse correlation between the expressions of acid invertase and SuSy-encoding genes, indicating that the balance between SuSy- and acid invertase-mediated sucrolytic pathways is a major determinant of Starch accumulation in potato tubers. Results presented in this work show that SuSy strongly determines the intracellular levels of UDPglucose, ADPglucose and Starch, and total yield in potato tubers. We also show that enhancement of SuSy activity represents a useful strategy for increasing Starch accumulation and yield in potato tubers.

Rapid Commun Mass Spectrom. 2009 Aug 30; 23(16): 2527-33
Maunoury-Danger F, Bathellier C, Laurette J, Fresneau C, Ghashghaie J, Damesin C, Tcherkez G

The delta(13)C (carbon isotope composition) variations in respired CO(2), total organic matter, proteins, sucrose and Starch have been measured during tuber sprouting of potato (Solanum tuberosum) in darkness. Measurements were carried out both on tubers and on their growing sprouts for 23 days after the start of sprout development. sucrose was slightly (13)C-depleted compared with Starch in tubers, suggesting that Starch breakdown was associated with a small isotope fractionation. In sprouts, all biochemical fractions including sucrose were (13)C-enriched compared with source tuber-sucrose, suggesting that sucrose translocation from tuber to sprouts fractionated against (12)C. However, both apparent fractionations were explained by the consumption of (13)C-depleted carbon for respiration or growth that enriched in the (13)C sucrose molecules left behind. In addition, whole tuber sucrose is constantly composed of recent sucrose from Starch breakdown and old sucrose associated with an inherited, slightly (13)C-depleted pool. We therefore conclude that any fractionation at either the Starch breakdown or the sucrose translocation level is unlikely under our conditions.

J Am Coll Nutr. 2009 Feb; 28(1): 30-6
Lioger D, Fardet A, Foassert P, Davicco MJ, Mardon J, Gaillard-Martinie B, Remesy C

BACKGROUND: Ready-to-eat breakfast cereals (RTE-BC) are eaten more and more frequently by both adults and adolescents, but their nutritional quality is far from satisfactory: they often contained too much sugars and lead to a high glycemic index (GI) which generally contributes to a more rapid return of the feeling of hunger favouring nibbling in the morning. OBJECTIVE: To reduce the GI and to improve the nutritional quality of standard wheat flakes (SWF) by adding a sourdough prefermentation step, suppressing steam cooking and decreasing the sucrose content (MWF, modified wheat flake). METHODS: Eleven healthy male volunteers were randomly given, at three separate times, SWF, MWF, and white-wheat bread (WWB, reference food). Plasma glucose, insulin and ghrelin concentrations were measured. The feeling of hunger was evaluated using a subjective rating scale. Starch structure of SWF and MWF was characterised by scanning electron microscopy. RESULTS: GI of MWF (83 +/- 7) was 12% lower than that of SWF (94 +/- 9) at 90 min but the effect was not significant. Insulinaemic index of MWF was significantly lower than that of SWF at 90 min (78 +/- 6 vs 98 +/- 8). Hunger feelings were lower following MWF consumption and were positively correlated (r = 0.98; P < 0.05) with plasma ghrelin concentrations, for which there was no significant difference between SWF and MWF. Starch granules of SWF were fully gelatinised unlike those of MWF. CONCLUSION: Despite its relatively high GI, MWF could provide health benefits by improving the management of hunger feeling in the morning and by moderately improving insulin economy, which could be of interest for type 2 diabetic subjects. GI is not, therefore, the sole parameter reflecting the nutritional quality of cereal products.

New Phytol. 2009; 184(1): 127-40
Kusch U, Greiner S, Steininger H, Meyer AD, Corbière-Divialle H, Harms K, Rausch T

Fifteen per cent of higher plants accumulate fructans. Plant development, nutritional status and stress exposure all affect fructan metabolism, and while fructan biochemistry is well understood, knowledge of its regulation has remained fragmentary. Here, we have explored chicory (Cichorium intybus) hairy root cultures (HRCs) to study the regulation of fructan metabolism in sink tissues in response to environmental cues. In standard medium (SM), HRCs did not accumulate inulin. However, upon transfer to high-carbon (C)/low-nitrogen (N) medium, expression of sucrose:sucrose 1-fructosyltransferase (1-SST) and fructan:fructan 1-fructosyltransferase (1-FFT) was strongly induced and inulin accumulated. Upon return to SM, inulin was degraded, together with a coordinate decline of 1-SST and 1-FFT expression. In HRCs, cold-induced expression of fructan 1-exohydrolases (1-FEH I and IIa) was similar to cold induction in taproots, even in the absence of accumulated inulin. For high-C/low-N induction of 1-SST and 1-FFT, and cold induction of 1-FEH I and IIa, the signaling pathways were addressed. While 1-SST and 1-FFT induction was similarly prevented by inhibitors of Ca(2+) signaling, protein kinases and phosphatases, cold induction of 1-FEH I and IIa revealed distinct signaling pathways. In summary, this study has established chicory HRCs as a convenient experimental system with which to study the regulation of fructan active enzyme (FAZY) expression in heterotrophic cells.

J Dairy Sci. 2009 Jul; 92(7): 3341-53
Penner GB, Oba M

The current study was undertaken to investigate the effect of feeding diets varying in sugar concentration to postpartum transition cows on productivity, ruminal fermentation, and nutrient digestibility. We hypothesized that the high-sugar diet would increase dry matter intake and lactation performance. The secondary objective was to characterize changes in ruminal fermentation and nutrient digestibility over the first 4 wk of lactation. Fifty-two Holstein cows, including 28 primiparous and 24 multiparous cows, 10 of which were previously fitted with a ruminal cannula, were assigned to the experimental diets containing either high sugar (HS = 8.4%) or low sugar (LS = 4.7%) immediately after calving, based on their expected calving date. Data and samples were collected on d 5.2 +/- 0.3, 12.2 +/- 0.3, 19.2 +/- 0.3, and 26.1 +/- 0.3 relative to parturition for wk 1, 2, 3, and 4 respectively. Cows fed HS had increased dry matter intake compared with those fed LS (18.3. vs. 17.2 kg/d). Further, cows fed HS sorted for particles retained on the pan of the Penn State Particle Size Separator to a greater extent than cows fed LS. Feeding HS tended to increase nadir (5.62 vs. 5.42), mean (6.21 vs. 6.06), and maximum pH (6.83 vs. 6.65). The duration (h/d) and area (pH x min/d) that ruminal pH was below pH 5.8 were not affected by treatment. Ruminal volatile fatty acid concentration and molar proportions of individual volatile fatty acids were not affected by treatment. The digestibility of dry matter, organic matter, neutral detergent fiber, and Starch were not affected by treatment, averaging 63.3, 65.2, 43.2, and 93.5%, respectively. Feeding HS decreased plasma glucose concentration compared with feeding LS (51.3 vs. 54.0 mg/dL), but concentration of plasma insulin was not affected by treatment, averaging 4.17 microIU/mL. Cows fed HS had higher concentrations of plasma beta-hydroxybutrate (17.5 vs. 10.5 mg/dL) and nonesterified fatty acids (344 vs. 280 microEq/L). Milk yield and milk composition were not affected by treatment, but a tendency for increased milk fat yield was observed for cows fed HS compared with LS (1.44 vs. 1.35 kg/d). The results of the current study imply that replacing cracked corn grain with sucrose may improve dry matter intake, ruminal pH status, and lactation performance.

Plant Signal Behav. 2008 Aug; 3(8): 525-36
Tuteja N, Sopory SK

Many chemicals are critical for plant growth and development and play an important role in integrating various stress signals and controlling downstream stress responses by modulating gene expression machinery and regulating various transporters/pumps and biochemical reactions. These chemicals include calcium (Ca(2+)), cyclic nucleotides, polyphosphoinositides, nitric oxide (NO), sugars, abscisic acid (ABA), jasmonates (JA), salicylic acid (SA) and polyamines. Ca(2+) is one of the very important ubiquitous second messengers in signal transduction pathways and usually its concentration increases in response to the stimuli including stress signals. Many Ca(2+) sensors detect the Ca(2+) signals and direct them to downstream signaling pathways by binding and activating diverse targets. cAMP or cGMP protects the cell with ion toxicity. Phosphoinositides are known to be involved both in transmission of signal across the plasma membrane and in intracellular signaling. NO activates various defense genes and acts as a developmental regulator in plants. Sugars affect the expression of many genes involved in photosynthesis, glycolysis, nitrogen metabolism, sucrose and Starch metabolism, defense mechanisms and cell cycle regulation. ABA, JA, SA and polyamines are also involved in many stress responses. Cross-talk between these chemical signaling pathways is very common in plant responses to abiotic and bitotic factors. In this article we have described the role of these chemicals in initiating signaling under stress conditions mainly the abiotic stress.

Plant Signal Behav. 2008 Jul; 3(7): 439-45
Baguma Y, Sun C, Borén M, Olsson H, Rosenqvist S, Mutisya J, Rubaihayo PR, Jansson C

Starch branching enzyme (SBE) activity in the cassava storage root exhibited a diurnal fluctuation, dictated by a transcriptional oscillation of the corresponding SBE genes. The peak of SBE activity coincided with the onset of sucrose accumulation in the storage, and we conclude that the oscillatory mechanism keeps the Starch synthetic apparatus in the storage root sink in tune with the flux of sucrose from the photosynthetic source. When storage roots were uncoupled from the source, SBE expression could be effectively induced by exogenous sucrose. Turanose, a sucrose isomer that cannot be metabolized by plants, mimicked the effect of sucrose, demonstrating that downstream metabolism of sucrose was not necessary for signal transmission. Also glucose and glucose-1-P induced SBE expression. Interestingly, induction by sucrose, turanose and glucose but not glucose-1-P sustained an overt semidian (12-h) oscillation in SBE expression and was sensitive to the hexokinase (HXK) inhibitor glucosamine. These results suggest a pivotal regulatory role for HXK during Starch synthesis. Abscisic acid (ABA) was another potent inducer of SBE expression. Induction by ABA was similar to that of glucose-1-P in that it bypassed the semidian oscillator. Both the sugar and ABA signaling cascades were disrupted by okadaic acid, a protein phosphatase inhibitor. Based on these findings, we propose a model for sugar signaling in regulation of Starch synthesis in the cassava storage root.

Parazitologiia. 2009 Mar-Apr; 43(2): 141-52
Izvekova GI

The bacteria capable of producing the enzymes hydrolyzing carbohydrates of various degrees of complexity (from Starch to sucrose) were found to be associated with the intestinal mucosa of fishes and tegument of cestodes. Presence of the bacteria displaying the sucrase activity is especially important for macroorganisms, as bacteriogenous glucose can be used by all members of the arising community. The greatest contribution to the hydrolysis of carbohydrates (both in host and parasite) is obviously made by those microorganisms which are more closely connected with the digestive-transport surfaces and are hardly removable from the intestines by peristalsis. The levels of total amylolytic activity of bacteriogenous enzymes and activity of their a-amylase under the experimental conditions are comparable to those of the enzymes involved in membrane digestion of the host and parasite, which can be evidence of the significant contribution of enzymes produced by symbiotic microflora to the digestive processes in macroorganisms.

Plant Physiol. 2009 Aug; 150(4): 1972-80
Maruyama K, Takeda M, Kidokoro S, Yamada K, Sakuma Y, Urano K, Fujita M, Yoshiwara K, Matsukura S, Morishita Y, Sasaki R, Suzuki H, Saito K, Shibata D, Shinozaki K, Yamaguchi-Shinozaki K

DREB1A/CBF3 and DREB2A are transcription factors that specifically interact with a cis-acting dehydration-responsive element (DRE), which is involved in cold- and dehydration-responsive gene expression in Arabidopsis (Arabidopsis thaliana). Overexpression of DREB1A improves stress tolerance to both freezing and dehydration in transgenic plants. In contrast, overexpression of an active form of DREB2A results in significant stress tolerance to dehydration but only slight tolerance to freezing in transgenic plants. The downstream gene products for DREB1A and DREB2A are reported to have similar putative functions, but downstream genes encoding enzymes for carbohydrate metabolism are very different between DREB1A and DREB2A. We demonstrate that under cold and dehydration conditions, the expression of many genes encoding Starch-degrading enzymes, sucrose metabolism enzymes, and sugar alcohol synthases changes dynamically; consequently, many kinds of monosaccharides, disaccharides, trisaccharides, and sugar alcohols accumulate in Arabidopsis. We also show that DREB1A overexpression can cause almost the same changes in these metabolic processes and that these changes seem to improve freezing and dehydration stress tolerance in transgenic plants. In contrast, DREB2A overexpression did not increase the level of any of these metabolites in transgenic plants. Strong freezing stress tolerance of the transgenic plants overexpressing DREB1A may depend on accumulation of these metabolites.

Arch Insect Biochem Physiol. 2009 Jul; 71(3): 139-58
Erban T, Erbanova M, Nesvorna M, Hubert J

The adaptation of nine species of mites that infest stored products for Starch utilization was tested by (1) enzymatic analysis using feces and whole mite extracts, (2) biotests, and (3) inhibition experiments. Acarus siro, Aleuroglyphus ovatus, and Tyroborus lini were associated with the Starch-type substrates and maltose, with higher enzymatic activities observed in whole mite extracts. Lepidoglyphus destructor was associated with the same substrates but had higher activities in feces. Dermatophagoides farinae, Chortoglyphus arcuatus, and Caloglyphus redickorzevi were associated with sucrose. Tyrophagus putrescentiae and Carpoglyphus lactis had low or intermediate enzymatic activity on the tested substrates. Biotests on Starch additive diets showed accelerated growth of species associated with the Starch-type substrates. The inhibitor acarbose suppressed Starch hydrolysis and growth of the mites. We suggest that the species with higher Starch hydrolytic activity in feces were more tolerant to acarbose, and alpha-amylase and alpha-glucosidase of synanthropic mites are suitable targets for inhibitor-based strategies of mite control.

Proc Natl Acad Sci U S A. 2009 Aug 4; 106(31): 13124-9
Barratt DH, Derbyshire P, Findlay K, Pike M, Wellner N, Lunn J, Feil R, Simpson C, Maule AJ, Smith AM

The entry of carbon from sucrose into cellular metabolism in plants can potentially be catalyzed by either sucrose synthase (SUS) or invertase (INV). These 2 routes have different implications for cellular metabolism in general and for the production of key metabolites, including the cell-wall precursor UDPglucose. To examine the importance of these 2 routes of sucrose catabolism in Arabidopsis thaliana (L.), we generated mutant plants that lack 4 of the 6 isoforms of SUS. These mutants (sus1/sus2/sus3/sus4 mutants) lack SUS activity in all cell types except the phloem. Surprisingly, the mutant plants are normal with respect to Starch and sugar content, seed weight and lipid content, cellulose content, and cell-wall structure. Plants lacking the remaining 2 isoforms of SUS (sus5/sus6 mutants), which are expressed specifically in the phloem, have reduced amounts of callose in the sieve plates of the sieve elements. To discover whether sucrose catabolism in Arabidopsis requires INVs rather than SUSs, we further generated plants deficient in 2 closely related isoforms of neutral INV predicted to be the main cytosolic forms in the root (cinv1/cinv2 mutants). The mutant plants have severely reduced growth rates. We discuss the implications of these findings for our understanding of carbon supply to the nonphotosynthetic cells of plants.