Kegg Pathway: Starch and sucrose metabolism

Plant Physiol Biochem. 2008 Nov 1;
Abbes Z, Kharrat M, Delavault P, Chaïbi W, Simier P

The parasitic weed Orobanche foetida (Poiret) is an emergent agronomical problem on faba bean in Tunisia. The Tunisian breeding programs for faba bean resistance to O. foetida have produced several tolerant lines including the line XBJ90.03-16-1-1-1, which limits both parasite attachments to the host roots and growth of the attached parasites. The present study aims to provide a better understanding of the nutritional relationships between the parasite and this tolerant line in comparison with the susceptible Bachaar genotype. Phloem saps of faba bean were harvested using phloem exudation experiments. The major organic compounds potentially transferred from both faba bean genotypes to the parasite were identified as sucrose, raffinose, stachyose, citrate, malate, asparagine (ASN), aspartate (ASP), glutamine, glutamate, serine, alanine and GABA. However, the phloem exudates of the tolerant line were highly deficient in nitrogen when compared to that of the susceptible line. When attached to roots of the tolerant line, the parasite displayed limited activities of soluble invertases in tubercles, and especially in shoots, suggesting that the low performance of the broomrapes attached to the tolerant line resulted from a reduced capacity to utilize the host-derived carbohydrates. On the other hand, the mechanisms involved in the osmotic adjustment and primary metabolism of the parasite did not differ significantly according to the host genotype: mineral cations, especially potassium and calcium, predominated as the major osmotically-active compounds in both tubercles and shoots; shoots accumulated preferentially hexoses as organic solutes although tubercles accumulated preferentially Starch and soluble amino acids, especially ASP and ASN. This suggests an important role for a glutamine-dependent asparagine synthetase (EC 6.3.5.4) in the N metabolism of the parasite.

J Exp Bot. 2008 Nov 25;
Bertin N, Causse M, Brunel B, Tricon D, Génard M

Many quantitative trait loci (QTLs) for quality traits have been located on the tomato genetic map, but introgression of favourable wild alleles into large fruited species is hampered by co-localizations of QTLs with antagonist effects. The aim of this study was to assess the growth processes controlled by the main QTLs for fruit size and composition. Four nearly isogenic lines (NILs) derived from an intraspecific cross between a tasty cherry tomato (Cervil) and a normal-tasting large fruit tomato (Levovil) were studied. The lines carried one (L2, L4, and L9) or five (Lx) introgressions from Cervil on chromosomes 1, 2, 4, and 9. QTLs for fruit size could be mainly associated with cell division processes in L2 and L9, whereas cell expansion was rather homogeneous among the genotypes, except Cervil for which the low expansion rate was attributed to low cell plasticity. The link between endoreduplication and fruit size remained unclear, as cell or fruit sizes were positively correlated with the cell DNA content, but not with the endoreduplication factor. QTLs for fruit composition reflected differences in water accumulation rather than in sugar accumulation, except in L9 for which the up-regulation of sucrose unloading and hexose transport and/or Starch synthesis was suggested. This may explain the increased amount of carbon allocated to cell structures in L9, which could be related to a QTL for fruit texture. In Lx, these effects were attenuated, except on fruit size and cell division. Finally, the region on top of chromosome 9 may control size and composition attributes in tomato, by a combination of QTL effects on cell division, cell wall synthesis, and carbon import and metabolism.

BMC Plant Biol. 2008 Nov 21; 8(1): 117
Fischer L, Lipavska H, Hausman JF, Opatrny Z

ABSTRACT: BACKGROUND: Tuberization in potato (Solanum tuberosum L.) represents a morphogenetic transition of stolon growth to tuber formation, which is under complex environmental and endogenous regulation. In the present work, we studied the regulatory mechanisms and the role of different morphogenetic factors in a newly isolated potato mutant, which exhibited spontaneous tuberization (ST). The ST mutant was characterized in detail at morphological, physiological and biochemical levels. RESULTS: Tuberization of the ST mutant grown in the soil was photoperiod-insensitive; predominantly sessile tubers formed directly from axillary buds even under continuous light. Single-node cuttings of the ST mutant cultured in vitro frequently formed tubers or basal tuber-like swellings instead of normal shoots under conditions routinely used for shoot propagation. The tuberization response of ST cuttings under light was dependent on sucrose, the concentration of which had to exceed certain threshold that inversely correlated with irradiance. Gibberellic acid prevented tuberization of ST cuttings, but failed to restore normal shoot phenotype and caused severe malformations. Carbohydrate analysis showed increased levels of both soluble sugars and Starch in ST plants, with altered carbohydrate partitioning and metabolism. Comparative proteomic analysis revealed only a few differences between ST- and wild-type plants, primary amongst which seemed to be the absence of an isoform of manganese-stabilizing protein, a key subunit of photosystem II. CONCLUSIONS: ST mutant exhibits complex developmental and phenotypic modifications, with features that are typical for plants strongly induced to tuberize. These changes are likely to be related to altered regulation of photosynthesis and carbohydrate metabolism rather than impaired transduction of inhibitory gibberellin or photoperiod-based signals. The effect of gibberellins on tuberization of ST mutant suggests that gibberellins inhibit tuberization downstream of the inductive effects of sucrose and other positive factors.

Indian J Exp Biol. 2008 Oct; 46(10): 736-42
Pattanagul W, Thitisaksakul M

Rice seedlings cv. Khao Dawk Mali 105 (salt-sensitive), Luang Anan (moderately salt-tolerant) and Pokkali (salt-tolerant) were exposed to 0, 50, 100 and 150 mM NaCI for 9 d. Salinity stress caused reduction in leaf relative water contents in all cultivars. Shoot length of cv. Pokkali was least affected by salinity stress whereas increased root length in response to salinity stress was apparent in cvs. Khao Dawk Mali 105 and Luang Anan. Increased salinity level also caused reduction in fresh and dry weights in cvs. Khao Dawk Mali 105 and Luang Anan, but had no effect in cv. Pokkali except at 150 mM. Accumulation of total soluble sugars and sucrose in mature leaves were observed in cv. Khao Dawk Mali 105 exposed to high level of salinity whereas their concentrations in cvs. Luang Anan and Pokkali remained the same as control plants. Accumulation of sucrose in cv. Khao Dawk Mali 105 was suggested to be resulted from the alteration of photosynthate partitioning since the activities of sucrose phosphate synthase were not affected by salinity in this cultivar. On the contrary, salinity stress induced an accumulation of Starch in cv. Pokkali. It is suggested that partitioning sugars into Starch may involve in salinity tolerance by avoiding metabolic alterations.

Plant Physiol. 2008 Nov 12;
Kreuzwieser J, Hauberg J, Howell KA, Carroll A, Rennenberg H, Millar AH, Whelan J

The molecular and physiological responses of Grey poplar (Populus x canescens) following root hypoxia were studied in roots and leaves using transcript and metabolite profiling. The results indicate that there were changes in metabolite levels in both organs, but changes in transcript abundance were restricted to the roots. In roots, Starch and sucrose degradation were altered under hypoxia, and concurrently, the availability of carbohydrates was enhanced, concomitant with depletion of sucrose from leaves and elevation of sucrose in the phloem. Consistent with the above, glycolytic flux and ethanolic fermentation were stimulated in roots but not leaves. Various mRNAs encoding components of biosynthetic pathways such as secondary cell wall formation, i.e. cellulose and lignin biosynthesis, and other energy demanding processes such as transport of nutrients, were significantly down-regulated in roots but not in leaves. The reduction of biosynthesis was unexpected, as shoot growth was not affected by root hypoxia suggesting that the up-regulation of glycolysis yields sufficient energy to maintain growth. Besides carbon metabolism, nitrogen metabolism was severely affected in roots as seen from numerous changes in the transcriptome and the metabolome related to N uptake, N assimilation, and amino acid metabolism. The coordinated physiological and molecular responses in leaves and roots, coupled with transport of metabolites reveal important stress adaptations to ensure survival during long periods of root hypoxia.

J Exp Bot. 2008 Oct 17;
Zhou Y, Chan K, Wang TL, Hedley CL, Offler CE, Patrick JW

Mechanistic inter-relationships in sinks between sucrose compartmentation/metabolism and phloem unloading/translocation are poorly understood. Developing grain legume seeds provide tractable experimental systems to explore this question. Metabolic demand by cotyledons is communicated to phloem unloading and ultimately import by sucrose withdrawal from the seed apoplasmic space via a turgor-homeostat mechanism. What is unknown is how metabolic demand is communicated to cotyledon sucrose transporters responsible for withdrawing sucrose from the apoplasmic space. This question was explored here using a pea rugosus mutant (rrRbRb) compromised in Starch biosynthesis compared with its wild-type counterpart (RRRbRb). sucrose influx into cotyledons was found to account for 90% of developmental variations in their absolute growth and hence Starch biosynthetic rates. Furthermore, rr and RR cotyledons shared identical response surfaces, indicating that control of transporter activity was likely to be similar for both lines. In this context, sucrose influx was correlated positively with expression of a sucrose/H(+) symporter (PsSUT1) and negatively with two sucrose facilitators (PsSUF1 and PsSUF4). sucrose influx exhibited a negative curvilinear relationship with cotyledon concentrations of sucrose and hexoses. In contrast, the impact of intracellular sugars on transporter expression was transporter dependent, with expression of PsSUT1 inhibited, PsSUF1 unaffected, and PsSUF4 enhanced by sugars. Sugar supply to, and sugar concentrations of, RR cotyledons were manipulated using in vitro pod and cotyledon culture. Collectively the results obtained showed that intracellular sucrose was the physiologically active sugar signal that communicated metabolic demand to sucrose influx and this transport function was primarily determined by PsSUT1 regulated at the transcriptional level.

Oral Dis. 2008 Sep; 14(6): 500-9
Sun QF, Sun QH, Du J, Wang S

BACKGROUND: Parotid and submandibular glands have different properties including characteristics of the secreted saliva and tumor incidences. The differences in properties of parotid and submandibular glands are not clear from a genetic viewpoint. OBJECTIVE: To study differential gene expression profiles between normal human parotid and submandibular glands. MATERIALS AND METHODS: Three pairs of normal parotid and submandibular glands were obtained. RNA was extracted from these samples. After reverse transcription, the cDNA was in vitro-transcribed to produce biotin-labeled cRNA. The purified biotin-labeled cRNA samples were hybridized to microarray chips. RESULTS: Among the 54 675 tested transcripts, 47 transcripts were upregulated at least twofold in the parotid gland compared with the submandibular gland, including tumor-associated genes (pleiotrophin, WNT5A, ABCC1) and transport-associated genes (SLCO1A2, SLC13A5, KCNJ15). Ninety-eight transcripts were upregulated at least twofold in the submandibular gland compared with the parotid gland, including the chloride channel CFTR and mucin-associated genes that belong to the Starch and sucrose metabolism pathway (GalNAc-T4, GalNAc-T7 and GalNAc-T13). Quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of nine differentially expressed genes confirmed the microarray results. CONCLUSION: This study revealed the different gene expression profiles of normal human parotid and submandibular glands, providing a genetic basis for their differing properties.

Plant Cell Environ. 2008 Sep 22;
Lee SK, Jeon JS, Börnke F, Voll L, Cho JI, Goh CH, Jeong SW, Park YI, Kim SJ, Choi SB, Miyao A, Hirochika H, An G, Cho MH, Bhoo SH, Sonnewald U, Hahn TR

To understand the carbon partitioning between sucrose and Starch in the source organs of the model monocot species, rice, this paper describes the physiological characterization of leaf carbohydrate metabolism in rice mutants lacking one key enzyme of the photosynthetic sucrose synthesis. Unlike the corresponding Arabidopsis mutant with no strong phenotype, rice mutants deficient in cytosolic fructose-1,6-bisphosphatase display severe growth retardation. Thus, this finding indicates that the impaired synthesis of sucrose in rice cannot be compensated by the transitory Starch-mediated pathways that have been found to facilitate plant growth in the Arabidopsis mutant.

Plant Physiol. 2008 Nov; 148(3): 1614-29
Fettke J, Nunes-Nesi A, Alpers J, Szkop M, Fernie AR, Steup M

The cytosolic pools of glucose-1-phosphate (Glc-1-P) and glucose-6-phosphate are essential intermediates in several biosynthetic paths, including the formation of sucrose and cell wall constituents, and they are also linked to the cytosolic Starch-related heteroglycans. In this work, structural features and biochemical properties of Starch-related heteroglycans were analyzed as affected by the cytosolic glucose monophosphate metabolism using both source and sink organs from wild-type and various transgenic potato (Solanum tuberosum) plants. In leaves, increased levels of the cytosolic phosphoglucomutase (cPGM) did affect the cytosolic heteroglycans, as both the glucosyl content and the size distribution were diminished. By contrast, underexpression of cPGM resulted in an unchanged size distribution and an unaltered or even increased glucosyl content of the heteroglycans. Heteroglycans prepared from potato tubers were found to be similar to those from leaves but were not significantly affected by the level of cPGM activity. However, external glucose or Glc-1-P exerted entirely different effects on the cytosolic heteroglycans when added to tuber discs. Glucose was directed mainly toward Starch and cell wall material, but incorporation into the constituents of the cytosolic heteroglycans was very low and roughly reflected the relative monomeric abundance. By contrast, Glc-1-P was selectively taken up by the tuber discs and resulted in a fast increase in the glucosyl content of the heteroglycans that quantitatively reflected the level of the cytosolic phosphorylase activity. Based on (14)C labeling experiments, we propose that in the cytosol, glucose and Glc-1-P are metabolized by largely separated paths.

Int J Syst Evol Microbiol. 2008 Sep; 58(Pt 9): 2132-5
Song L, Dong X

A Gram-stain-positive, strictly anaerobic, mesophilic, amylolytic, rod-shaped bacterium, designated strain SW408(T), was isolated from a laboratory-scale H(2)-producing upflow anaerobic sludge blanket reactor. The strain grew at 24-45 degrees C (no growth at or below 22 degrees C or at or above 47 degrees C), with optimum growth at 37 degrees C. The pH range for growth was 4.0-9.0 (no growth at or below pH 3.6 or at or above pH 9.3), with optimum growth at pH 7.0. Starch, cellobiose, glucose, fructose, galactose, lactose, maltose, mannose, ribose and sucrose supported growth. The major end products from glucose fermentation were ethanol, acetate, hydrogen and carbon dioxide. Abundant H(2) was produced from Starch fermentation. The DNA G+C content was 33.1 mol% (T(m) method). Phylogenetic analysis based on 16S rRNA gene sequence analysis showed that the bacterium represents a previously unrecognized species within Clostridium rRNA cluster I and is most closely related to the type strain of Clostridium frigidicarnis (94.9% similarity). On the basis of phenotypic, genotypic and phylogenetic characteristics, strain SW408(T) was identified as a representative of a novel species of the genus Clostridium, for which the name Clostridium amylolyticum sp. nov. is proposed. The type strain is SW408(T) (=JCM 14823(T)=AS 1.5069(T)=CGMCC 1.5069(T)).

Physiol Plant. 2008 Aug; 133(4): 692-704
Cakmak I, Kirkby EA

Magnesium (Mg) deficiency exerts a major influence on the partitioning of dry matter and carbohydrates between shoots and roots. One of the very early reactions of plants to Mg deficiency stress is the marked increase in the shoot-to-root dry weight ratio, which is associated with a massive accumulation of carbohydrates in source leaves, especially of sucrose and Starch. These higher concentrations of carbohydrates in Mg-deficient leaves together with the accompanying increase in shoot-to-root dry weight ratio are indicative of a severe impairment in phloem export of photoassimilates from source leaves. Studies with common bean and sugar beet plants have shown that Mg plays a fundamental role in phloem loading of sucrose. At a very early stage of Mg deficiency, phloem export of sucrose is severely impaired, an effect that occurs before any noticeable changes in shoot growth, Chl concentration or photosynthetic activity. These findings suggest that accumulation of carbohydrates in Mg-deficient leaves is caused directly by Mg deficiency stress and not as a consequence of reduced sink activity. The role of Mg in the phloem-loading process seems to be specific; resupplying Mg for 12 or 24 h to Mg-deficient plants resulted in a very rapid recovery of sucrose export. It appears that the massive accumulation of carbohydrates and related impairment in photosynthetic CO2 fixation in Mg-deficient leaves cause an over-reduction in the photosynthetic electron transport chain that potentiates the generation of highly reactive O2 species (ROS). Plants respond to Mg deficiency stress by marked increases in antioxidative capacity of leaves, especially under high light intensity, suggesting that ROS generation is stimulated by Mg deficiency in chloroplasts. Accordingly, it has been found that Mg-deficient plants are very susceptible to high light intensity. Exposure of Mg-deficient plants to high light intensity rapidly induced leaf chlorosis and necrosis, an outcome that was effectively delayed by partial shading of the leaf blade, although the Mg concentrations in different parts of the leaf blade were unaffected by shading. The results indicate that photooxidative damage contributes to development of leaf chlorosis under Mg deficiency, suggesting that plants under high-light conditions have a higher physiological requirement for Mg. Maintenance of a high Mg nutritional status of plants is, thus, essential in the avoidance of ROS generation, which occurs at the expense of inhibited phloem export of sugars and impairment of CO2 fixation, particularly under high-light conditions.

J Hered. 2008 Nov-Dec; 99(6): 661-6
Slewinski TL, Ma Y, Baker RF, Huang M, Meeley R, Braun DM

In regions of their leaves, tdy1-R mutants hyperaccumulate Starch. We propose 2 alternative hypotheses to account for the data, that Tdy1 functions in Starch catabolism or that Tdy1 promotes sucrose export from leaves. To determine whether Tdy1 might function in Starch breakdown, we exposed plants to extended darkness. We found that the tdy1-R mutant leaves retain large amounts of Starch on prolonged dark treatment, consistent with a defect in Starch catabolism. To further test this hypothesis, we identified a mutant allele of the leaf expressed small subunit of ADP-glucose pyrophosphorylase (agps-m1), an enzyme required for Starch synthesis. We determined that the agps-m1 mutant allele is a molecular null and that plants homozygous for the mutation lack transitory leaf Starch. Epistasis analysis of tdy1-R; agps-m1 double mutants demonstrates that Tdy1 function is independent of Starch metabolism. These data suggest that Tdy1 may function in sucrose export from leaves.

Biochem Biophys Res Commun. 2008 Oct 31; 375(4): 592-5
Cook LB, Delorme-Axford EB, Robinson K

The melanin-concentrating hormone receptor (MCHR) 1 is a G protein-coupled receptor involved in the regulation of appetite and energy expenditure in mammals. Here, we show that MCHR1 partitions to lipid rafts in stably expressing Chinese hamster ovary cells. In addition to co-fractionating with lipid rafts containing caveolin-1 on sucrose gradients, caveolin-1 was present in MCHR1 immunoprecipitates, suggesting that MCHR1 complexes with caveolae. The cholesterol-depleting drug methyl-beta-cyclodextrin impaired MCH-mediated ERK signaling. These data suggest that a functional interaction between MCHR1 and caveolin-1 in lipid rafts exists and provide a basis for further biochemical studies to understand the significance on MCH-mediated signal transduction events.

J Integr Plant Biol. 2008 Jun; 50(6): 733-41
Wang DY, Lian Y, Zhu DW

APase activity is involved in regulating many physiological and developmental events by affecting the resorption process. In this study, we investigate the role of APase activity in tuber development in potato. APase activities were mainly localized in cytoplasm, gaps among cells and stroma of amyloplasts of parenchyma cells at the stage of tuber swelling. AP1, encoding a putative APase, was also highly expressed in swelling tubers and a low level of expression was observed in elongated stolons and matured tubers. Inhibition of APase activity by applying Brefeldin A, an inhibitor of APase production and secretion, significantly suppressed the tuber swelling and moderately affected the stolon elongation and the tuberization frequency. During tuber development, sucrose serves as the main soluble sugar for long-distance transportation and resorption. Moreover, inhibition of APase activity by Brefeldin A markedly reduced the sucrose content in tubers and further decreased the Starch accumulation, suggesting that the function of APase in regulating the tuber swelling might be at least partially mediated by the sugar resorption. Exogenous sucrose treatments further indicate the important role of sucrose-mediated sugar resorption in tuber swelling. These results suggest that the APase activity might affect the tuber swelling by partially regulating the sucrose-mediated sugar resorption.

J Integr Plant Biol. 2008 Jun; 50(6): 723-32
Li JY, Liu XH, Cai QS, Gu H, Zhang SS, Wu YY, Wang CJ

To study the effects of growing rice (Oryza sativa L.) leaves under the treatment of the short-term elevated CO(2) during the period of sink-source transition, several physiological processes such as dynamic changes in photosynthesis, photosynthate accumulation, enzyme activities (sucrose phosphate synthase (SPS), and sucrose synthase (SS)), and their specific gene (sps1 and RSus1) expressions in both mature and developing leaf were measured. Rice seedlings with fully expanded sixth leaf (marked as the source leaf, L6) were kept in elevated (700 micromol/mol) and ambient (350 mol/L) CO(2) until the 7th leaf (marked as the sink leaf, L7) fully expanded. The results demonstrated that elevated CO(2) significantly increased the rate of leaf elongation and biomass accumulation of L7 during the treatment without affecting the growth of L6. However, in both developing and mature leaves, net photosynthetic assimilation rate (A), all kinds of photosynthate contents such as Starch, sucrose and hexose, activities of SPS and SS and transcript levels of sps1 and RSus1 were significantly increased under elevated CO(2) condition. Results suggested that the elevated CO(2) had facilitated photosynthate assimilation, and increased photosynthate supplies from the source leaf to the sink leaf, which accelerated the growth and sink-source transition in new developing sink leaves. The mechanisms of SPS regulation by the elevated CO(2) was also discussed.

Channels (Austin). 2007 Jul-Aug; 1(4): 263-72
Balijepalli RC, Delisle BP, Balijepalli SY, Foell JD, Slind JK, Kamp TJ, January CT

The localization of ion channels to specific membrane microdomains can impact the functional properties of channels and their role in cellular physiology. We determined the membrane localization of human Kv11.1 (hERG1) alpha-subunit protein, which underlies the rapidly activating, delayed rectifier K(+) current (I(Kr)) in the heart. Immunocytochemistry and membrane fractionation using discontinuous sucrose density gradients of adult canine ventricular tissue showed that Kv11.1 channel protein localized to both the cell surface and T-tubular sarcolemma. Furthermore, density gradient membrane fractionation using detergent (Triton X-100) and non-detergent (OptiPrep) methods from canine ventricular myocytes or HEK293 cells demonstrated that Kv11.1 protein, along with MiRP1 and Kv7.1 (KCNQ1) proteins, localize in cholesterol and sphingolipid enriched membrane fractions. In HEK293 cells, Kv11.1 channels, but not long QT-associated mutant G601S-Kv11.1 channels, also localized to cholesterol and sphingolipid enriched membrane fractions. Depletion of membrane cholesterol from HEK293 cells expressing Kv11.1 channels using methyl-beta-cyclodextrin (MbetaCD) caused a positive shift of the voltage dependence of activation and an acceleration of deactivation kinetics of Kv11.1 current (I(Kv11.1)). Cholesterol loading of HEK293 cells reduced the steep voltage dependence of I(Kv11.1) activation and accelerated the inactivation kinetics of I(Kv11.1). Incubation of neonatal mouse myocytes in MbetaCD also accelerated the deactivation kinetics of I(Kr). We conclude that Kv11.1 protein localizes in cholesterol and sphingolipid enriched membranes and that membrane cholesterol can modulate I(Kv11.1) and I(Kr).

Plant Physiol. 2008 Sep; 148(1): 316-27
van Heerden PD, Kiddle G, Pellny TK, Mokwala PW, Jordaan A, Strauss AJ, de Beer M, Schlüter U, Kunert KJ, Foyer CH

Symbiotic nitrogen fixation is sensitive to dark chilling (7 degrees C-15 degrees C)-induced inhibition in soybean (Glycine max). To characterize the mechanisms that cause the stress-induced loss of nodule function, we examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN), which is chilling sensitive, and Highveld Top (HT), which is more chilling resistant. Nodule numbers were unaffected by dark chilling, as was the abundance of the nitrogenase and leghemoglobin proteins. However, dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs and incre