Kegg Pathway: Starch and sucrose metabolism

KEGG ID: 00500

Reference Diagram

KEGG Diagram for Starch and sucrose metabolism

Rat

There are 39 IPI Records from this pathway found in Rattus norvegicus.

Location of Starch and sucrose metabolism proteins on Rat Genome

IPI Record Position
1: Amy1 2:209548721-209563532
2: Ddx18 13:33587928-33601436
3: Ddx4 :-
4: Ddx52 10:72222687-72245432
5: Enpp1 1:21223674-21287411
6: Enpp2 7:91296289-91377765
7: Enpp3 1:21087399-21159922
8: G6pc 10:90393597-90403140
9: Gaa :-
10: Gbe1 11:8720408-8975223
11: Gck 14:86572518-86587740
12: Gusb 12:27741165-27770815
13: Gys2 4:179984802-180018774
14: Hk1 :-
15: Hk2 4:116925725-116975211
16: Hk3 17:15651953-15669109
17: Pgm1 5:120595650-120655915
18: Pygb 3:141421448-141468085
19: Pygl 6:92298334-92341397
20: Pygm 1:209166701-209181588
21: RGD1305984 2:44247873-44306048
22: Si 2:163521423-163600349
23: Udpgtr2 14:22639182-22650931
24: Ugdh 14:45542781-45570961
25: Ugt1a1 9:87017029-87098362
26: Ugt1a10 :-
27: Ugt1a2 :-
28: Ugt1a3 9:87017029-87098362
29: Ugt1a5 :-
30: Ugt1a6 9:87017029-87098362
31: Ugt1a7 9:87017029-87098362
32: Ugt1a8 9:87017029-87098362
33: Ugt2a1 14:21962679-22071687
34: Ugt2a3_predicted 14:22097961-22116820
35: Ugt2b 14:22154728-22177507
36: Ugt2b3 :-
37: Ugt2b4 14:22454256-22493510
38: Ugt2b5 14:22346364-22422959
39: Uxs1 :-

Mouse

There are 39 IPI Records from this pathway found in Mus musculus.

Location of Starch and sucrose metabolism proteins on Mouse Genome

IPI Record Position
1: Agl 3:116735055-116750309
2: Amy1 3:113547957-113569751
3: Ascc3 10:50281122-50539005
4: Ascc3l1 2:126899840-126931894
5: Ddx18 1:123381385-123395480
6: Ddx23 15:98473828-98490918
7: Ddx4 13:113719214-113773179
8: Ddx41 13:55540039-55546143
9: Ddx47 6:134977313-134989464
10: Ddx50 10:62011380-62046575
11: Ddx51 5:110893776-110900614
12: Ddx52 11:83758373-83778389
13: Ddx54 5:120873747-120889209
14: Ddx56 11:6157548-6167732
15: Enpp1 10:24330827-24401518
16: Enpp2 15:54668984-54750085
17: Enpp3 10:24463318-24525509
18: Ep400 5:110904680-111010829
19: Ercc2 7:18540561-18554214
20: Ercc3 18:32383341-32413157
21: G6pc :-
22: Gaa 11:119084118-119101544
23: Gbe1 16:70196743-70452387
24: Gck 11:5800826-5850084
25: Gpi1 7:33910087-33939000
26: Gusb 5:130273725-130287564
27: Gys1 7:45303088-45324144
28: Gys2 6:142379835-142430179
29: Hk2 6:82690705-82740117
30: Hk3 13:55015608-55030956
31: Ifih1 2:62398289-62446999
32: IPI00756791 3:72976489-73054795
33: Mov10l1 15:88813324-88882914
34: Nudt16 9:104987773-104989880
35: Nudt5 2:5762306-5786008
36: Nudt8 19:4000580-4002102
37: OTTMUSG00000022462 3:113515321-113524293
38: Pgm2 5:64372085-64407313
39: Pygb 2:150478229-150523191
40: Pygl 12:71109416-71146222
41: Pygm 19:6384429-6398459
42: Rad54l 4:115594848-115621617
43: Ruvbl2 7:45289939-45306138
44: Skiv2l2 13:113988658-114048258
45: Smarca5 8:83595689-83635205
46: Ugdh 5:65692354-65714977
47: Ugp2 11:21221141-21270480
48: Ugt1a1 :-
49: Ugt1a10 :-
50: Ugt1a5 :-
51: Ugt1a6a 1:89901971-90050174
52: Ugt1a6b :-
53: Ugt1a7c 1:89901971-90050174
54: Ugt1a9 1:89901971-90050174
55: Ugt2a1 5:88534051-88565420
56: Ugt2a2 :-
57: Ugt2a3 5:88399533-88411737
58: Ugt2b1 5:87991199-88001091
59: Ugt2b5 5:88199521-88214879
60: Uxs1 1:43693833-43772294

Human

There are 39 IPI Records from this pathway found in Homo sapiens.

Location of Starch and sucrose metabolism proteins on Human Genome

IPI Record Position
1: AGL 1:100088228-100162164
2: AMY2A 1:103961522-103969925
3: AMY2B 1:103897960-103923675
4: ASCC3 6:101062791-101435961
5: ASCC3L1 2:96303804-96334988
6: ATP13A2 1:17185040-17210997
7: DDX18 2:118288725-118306425
8: DDX19A 16:68938287-68964780
9: DDX23 12:47509807-47532224
10: DDX4 5:55069609-55148362
11: DDX41 5:176871185-176876557
12: DDX47 12:12770130-12874176
13: DDX50 10:70331040-70376609
14: DDX51 12:131190033-131194806
15: DDX52 17:33046526-33077600
16: DDX54 12:112079369-112107667
17: DDX55 12:122652625-122671433
18: DDX56 7:44571929-44581175
19: DHX58 17:37506979-37518277
20: ENPP1 6:132170849-132257988
21: ENPP2 8:120638507-120720260
22: ENPP3 6:132000135-132110243
23: EP400 12:131000461-131130958
24: ERCC2 19:50546686-50565669
25: ERCC3 2:127731336-127768222
26: G6PC 17:38306341-38318912
27: G6PC2 2:169466047-169474750
28: GAA 17:75689877-75708273
29: GANC 15:40353658-40491807
30: GBA 1:153470867-153481112
31: GBA3 4:22303686-22430289
32: GBE1 3:81621542-81894002
33: GCK 7:44150395-44195563
34: GPI 19:39547727-39583072
35: GUSB 7:65063110-65084635
36: GYS1 19:54163195-54188379
37: GYS2 12:21580392-21648821
38: HK1 10:70699762-70831644
39: HK2 2:74913290-74973982
40: HK3 5:176240680-176259284
41: IFIH1 2:162831836-162883285
42: LYZL1 10:29617996-29640167
43: MGAM 7:141342148-141507472
44: MOV10L1 22:48870621-48942242
45: NUDT5 10:12247330-12278129
46: NUDT8 11:67151986-67153977
47: PGM1 1:63831535-63898504
48: PGM3 6:83933025-83959701
49: PYGB 20:25176706-25226648
50: PYGL 14:50441718-50480942
51: PYGM 11:64270437-64284763
52: RAD54B 8:95453365-95556486
53: RAD54L 1:46485991-46516731
54: RUVBL2 19:54007256-54210952
55: SETX 9:134129104-134220193
56: SI 3:166179381-166278976
57: SKIV2L2 5:54639345-54757166
58: SMARCA2 9:2005342-2183624
59: SMARCA5 4:144654066-144694016
60: TREH 11:118034209-118055592
61: UGDH 4:39176770-39205613
62: UGP2 2:63922518-63972196
63: UGT1A6 2:234191030-234346695
64: UGT1A7 2:234191030-234346695
65: UGT1A8 2:234191030-234346695
66: UGT1A9 2:234191030-234346695
67: UGT2A1 4:70489562-70548007
68: UGT2A3 4:69828756-69852093
69: UGT2B10 4:69716302-69731214
70: UGT2B11 4:69905135-70115054
71: UGT2B15 4:69546976-69570979
72: UGT2B17 4:69085500-69116840
73: UGT2B28 4:70180783-70323496
74: UGT2B4 4:70380474-70396212
75: UGT2B7 4:69996782-70013141
76: UXS1 2:106076203-106177189

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Recent Literature

Nitrogen and carbon relationships between the parasitic weed Orobanche foetida and susceptible and tolerant faba bean lines.

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.

Identification of growth processes involved in QTLs for tomato fruit size and composition.

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.

Morphological and molecular characterization of a spontaneously tuberizing potato mutant: an insight into the regulatory mechanisms of tuber induction.

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.

Effect of salinity stress on growth and carbohydrate metabolism in three rice (Oryza sativa L.) cultivars differing in salinity tolerance.

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.

Differential response of poplar (P. x canescens) leaves and roots underpins stress adaptation during hypoxia.

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.

Intracellular sucrose communicates metabolic demand to sucrose transporters in developing pea cotyledons.

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.

Differential gene expression profiles of normal human parotid and submandibular glands.

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.

Loss of cytosolic fructose-1,6-bisphosphatase limits photosynthetic sucrose synthesis and causes severe growth retardations in rice (Oryza sativa).

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.

Alterations in cytosolic glucose-phosphate metabolism affect structural features and biochemical properties of Starch-related heteroglycans.

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.

Clostridium amylolyticum sp. nov., isolated from H2-producing UASB granules.

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)).

Role of magnesium in carbon partitioning and alleviating photooxidative damage.

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.

Determining the role of Tie-dyed1 in Starch metabolism: epistasis analysis with a maize ADP-glucose pyrophosphorylase mutant lacking leaf Starch.

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.

Caveolae as potential mediators of MCH-signaling pathways.

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.

Acid phosphatase activity may affect the tuber swelling by partially regulating sucrose-mediated sugar resorption in potato.

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.

Effects of elevated CO2 on growth, carbon assimilation, photosynthate accumulation and related enzymes in rice leaves during sink-source transition.

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.

Kv11.1 (ERG1) K+ channels localize in cholesterol and sphingolipid enriched membranes and are modulated by membrane cholesterol.

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).

Regulation of respiration and the oxygen diffusion barrier in soybean protect symbiotic nitrogen fixation from chilling-induced inhibition and shoots from premature senescence.

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