Low Molecular Weight Subunits Research Articles

Deletion of psbJ leads to accumulation of Psb27–Psb28 photosystem II complexes in Thermosynechococcus elongatus

The life cycle of Photosystem II (PSII) is embedded in a network of proteins that guides the complex through biogenesis, damage and repair. Some of these proteins, such as Psb27 and Psb28, are involved in cofactor assembly for which they are only transiently bound to the preassembled complex. In this work we isolated and analyzed PSII from a ΔpsbJ mutant of the thermophilic cyanobacterium Thermosynechococcus elongatus. From the four different PSII complexes that could be separated the most prominent one revealed a monomeric Psb27–Psb28 PSII complex with greatly diminished oxygen-evolving activity. The MALDI-ToF mass spectrometry analysis of intact low molecular weight subunits (<10kDa) depicted wild type PSII with the absence of PsbJ. Relative quantification of the PsbA1/PsbA3 ratio by LC-ESI mass spectrometry using 15N labeled PsbA3-specific peptides indicated the complete replacement of PsbA1 by the stress copy PsbA3 in the mutant, even under standard growth conditions (50μmol photons m−2 s−1). This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Response to Cutaneous Immunization with Low Molecular Weight Subunit Keyhole Limpet Hemocyanin (KLH)

Background: This study was carried out to determine whether humoral and cellular immune responses would be provoked by cutaneous administration of keyhole limpet hemocyanin (KLH) and in particular by scarification of the skin (SS). Methods: This was an unblinded, single-center, 8-week pilot study in healthy young adults. Twenty-four subjects assigned to 4 groups completed the study. Each group was immunized twice, with a 3-week interval, either by SS or intradermally (ID), with an SS dose of 50 or 250 g and an ID dose of 100 or 250 g. Serum was collected for antibody assays at baseline and 3 weeks after both the first and second immunizations. Delayed-type hypersensitivity (DTH) testing was performed before the first immunization and 3 weeks after the second. Results: In the 250- g SS group, there was a significant increase from day 0 to day 47 in anti-KLH IgG (p = 0.02; day 0: 3.46 8 5.49 mg/dl, day 47: 7.54 8 8.87 mg/dl) and anti-KLH IgA (p = 0.04; day 0: 4.78 8 9.15 mg/dl, day 47: 11.42 8 13.62 mg/dl). One subject in each treatment group showed a positive DTH test result representing 20% (50- g SS), 10% (250- g SS), 25% (100- g ID) and 20% (250- g ID) of the sub

Roles of PsbI and PsbM in photosystem II dimer formation and stability studied by deletion mutagenesis and X-ray crystallography

PsbM and PsbI are two low molecular weight subunits of photosystem II (PSII), with PsbM being located in the center, and PsbI in the periphery, of the PSII dimer. In order to study the functions of these two subunits from a structural point of view, we crystallized and analyzed the crystal structure of PSII dimers from two mutants lacking either PsbM or PsbI. Our results confirmed the location of these two subunits in the current crystal structure, as well as their absence in the respective mutants. The relative contents of PSII dimers were found to be decreased in both mutants, with a concomitant increase in the amount of PSII monomers, suggesting a destabilization of PSII dimers in both of the mutants. On the other hand, the accumulation level of the overall PSII complexes in the two mutants was similar to that in the wild-type strain. Treatment of purified PSII dimers with lauryldimethylamine N-oxide at an elevated temperature preferentially disintegrated the dimers from the PsbM deletion mutant into monomers and CP43-less monomers, whereas no significant degradation of the dimers was observed from the PsbI deletion mutant. These results indicate that although both PsbM and PsbI are required for the efficient formation and stability of PSII dimers in vivo, they have different roles, namely, PsbM is required directly for the formation of dimers and its absence led to the instability of the dimers accumulated. On the other hand, PsbI is required in the assembly process of PSII dimers in vivo; once the dimers are formed, PsbI was no longer required for its stability.

Analysis of HMWGS of historical set of Pakistani bread wheat varieties using SDS-PAGE

In the present study an attempt has been made to characterize thirty bread-wheat varieties of Pakistan for High Molecular Weight Glutenin Subunits (HMW- GS). Glutenin proteins form a continuous proteinaceous matrix in the cells and form a continuous viscoelastic network during the mixing process of dough development. Glutenin consists of High Molecular Weight (HMW) and Low Molecular Weight (LMW) subunits. The HMW Glutenin Subunits (HMW-GS) are chiefly vital for determining dough elasticity. The core objective of our research work was to inspect the glutenin subunits by sodium dodecyl-sulfate polyacrylamide gel-electrophoresis (SDS-PAGE) and compare the banding pattern with Chinese Spring High-Molecular-Weight Glutenin Subunits (HMW-GS). The bands were numbered according to Payne's numbering system and varieties were accordingly assigned theoretical quality scores. All the tested varieties indicated null allele for gluA1 locus, 17 + 18 for gluB1 locus and 2 + 12 for gluD1 locus. This result indicating that all varieties have similar bread making quality alleles at HMWGS loci. The varieties containing 5 + 10 HMWGS allele at gluD1 locus have better bread making quality. Better bread making wheat varieties may be produced by crossing the local varieties of gluA1 locus, 17 + 18 for gluB1 locus and 2 + 12 for gluD1 locus with 5 + 10 HMWGS allele at gluD1 locus.

Influence of water deficit on durum wheat storage protein composition and technological quality

Two durum wheat ( Triticum durum Desf.) cultivars (Simeto and Ofanto) were grown in field trials in Foggia (Southern Italy), under two water regimes and in three cropping seasons, to evaluate the influence of water regime on grain protein composition in relation to technological quality. On grain samples, the following quality analyses were performed: protein and gluten content, gluten index and SDS test. Furthermore, different protein fractions were evaluated: gliadins; glutenins, high molecular weight subunits (HMW-GS) and low molecular weight subunits (LMW-GS) of the larger glutenin polymers; percentage of unextractable polymeric proteins (%UPP). Two-dimensional gel electrophoresis (2D) of glutenins was also performed on selected samples. A year-on-year variation in gluten index was observed and its values were positively correlated ( r = 0.71**) with the number of days with maximum temperature ranging from 30 to 35 °C during grain filling. This was consistent with an increase in glutenin fractions. Between the investigated cultivars, Simeto showed better technological performance and higher glutenin content, HMW-GS/LMW-GS ratio and %UPP. Water deficit was found to affect technological quality and protein composition differently depending on the timing of stress occurrence. An increase in protein content and in HMW-GS/LMW-GS ratio, consistent with a decrease in grain yield, was observed when water deficit occurred throughout the growing season. When a terminal water stress occurred in grain filling an improvement in gluten strength was observed consistently with an increase in the amount of glutenin macropolymers associated to a general modulation of HMW-GS and LMW-GS levels, as indicated by 2D analyses. Probably water deficit associated to high temperature stress which generally occurs under Mediterranean environments during grain filling, may have caused a higher aggregation level of glutenin subunits that was reflected in an improvement of technological quality.

Assessment of genetic diversity among Pakistani wheat (Triticum aestivum L.) advanced breeding lines using rapd and sds-page

Genetic diversity was assessed among 32 advanced wheat breeding lines included in the National Uniform Wheat Yield Trials (2006-07) of Pakistan using molecular (DNA) and biochemical (SDS-PAGE) markers. Of the 72 RAPD primers used for initial screening, 15 were found polymorphic. A total of 140 bands (61.4% polymorphic) were generated by the 15 random decamer primers. Genetic similarity coefficients ranged from 0.81 to 0.94 for rainfed and from 0.70 to 0.93 for the normal seeding date group. Cluster analysis using the unweighted pair group method of arithmetic averages (UPGMA) clustered the 32 advanced wheat breeding lines into one major and three small groups. Maximum level of polymorphism (90%) was observed for the primer OPA-05. Lines N9 and N11 showed the least genetic similarities (0.70-0.82 and 0.71-0.83, respectively) with rest of the lines studied. Line RF1 had the maximum similarity (0.81-0.94) with other lines. Wheat lines included in the normal seeding date were relatively distantly related than those in the rainfed group. Seed storage protein analysis produced 19 subunits ranging from 29-120KDa. Similarity coefficients ranged from 0.53 to 1.0 for the normal seeding date and from 0.47 to 1.0 for the rainfed group. High molecular weight subunits (particularly 120KDa) showed greater polymorphism than the lower molecular weight subunits. Narrow genetic base was observed in wheat lines included in the rainfed group. DNA fingerprinting of advanced breeding lines may help to avoid release of varieties with narrow genetic base in the future.

Structural and functional studies on Ycf12 (Psb30) and PsbZ-deletion mutants from a thermophilic cyanobacterium

Ycf12 (Psb30) and PsbZ are two low molecular weight subunits of photosystem II (PSII), with one and two trans-membrane helices, respectively. In order to study the functions of these two subunits from a structural point of view, we constructed deletion mutants lacking either Ycf12 or PsbZ from Thermosynechococcus elongatus, and purified, crystallized and analyzed the structure of PSII dimer from the two mutants. Our results showed that Ycf12 is located in the periphery of PSII, close to PsbK, PsbZ and PsbJ, and corresponded to the unassigned helix X1 reported previously, in agreement with the recent structure at 2.9 Å resolution (A. Guskov, J. Kern, A. Gabdulkhakov, M. Broser, A. Zouni, W. Saenger, Cyanobacterial photosystem II at 2.9 Å resolution: role of quinones, lipids, channels and chloride, Nat. Struct. Mol. Biol. 16 (2009) 334–342). On the other hand, crystals of PsbZ-deleted PSII showed a remarkably different unit cell constants from those of wild-type PSII, indicating a role of PsbZ in the interactions between PSII dimers within the crystal. This is the first example for a different arrangement of PSII dimers within the cyanobacterial PSII crystals. PSII dimers had a lower oxygen-evolving activity from both mutants than that from the wild type. In consistent with this, the relative content of PSII in the thylakoid membranes was lower in the two mutants than that in the wild type. These results suggested that deletion of both subunits affected the PSII activity, thereby destabilized PSII, leading to a decrease in the PSII content in vivo. While PsbZ was present in PSII purified from the Ycf12-deletion mutant, Ycf12 was present in crude PSII but absent in the finally purified PSII from the PsbZ-deletion mutant, indicating a preferential, stabilizing role of PsbZ for the binding of Ycf12 to PSII. These results were discussed in terms of the PSII crystal structure currently available.

Renal AA amyloidosis secondary to morbid obesity?

Systemic amyloidosis is characterized by extracellular deposits on different organs of insoluble fibrils compounded of low molecular weight subunits coming from a great diversity of serum proteins. Secondary amyloidosis AA is due to fibril deposition composed of fragments of the acute phase reactant serum amyloid A. We report a case of a young patient with morbid obesity and hypertension who was admitted to our hospital for acute renal insufficiency associated with nephrotic range proteinuria which developed while on antibiotic treatment for a respiratory infection. AA Amyloidosis was diagnosed by renal biopsy. Based on recent evidence we hypothesize that morbid obesity could be the underlying cause of the deposit disease.

Trafficking of storage proteins in developing grain of wheat

The processing properties of the wheat flour are largely determined by the structures and interactions of the grain storage proteins (also called gluten proteins) which form a continuous visco-elastic network in dough. Wheat gluten proteins are classically divided into two groups, the monomeric gliadins and the polymeric glutenins, with the latter being further classified into low molecular weight (LMW) and high molecular weight (HMW) subunits. The synthesis, folding and deposition of the gluten proteins take place within the endomembrane system of the plant cell. However, determination of the precise routes of trafficking and deposition of individual gluten proteins in developing wheat grain has been limited in the past by the difficulty of developing monospecific antibodies. To overcome this limitation, a single gluten protein (a LMW subunit) was expressed in transgenic wheat with a C-terminal epitope tag, allowing the protein to be located in the cells of the developing grain using highly specific antibodies. This approach was also combined with the use of wider specificity antibodies to compare the trafficking and deposition of different gluten protein groups within the same endosperm cells. These studies are in agreement with previous suggestions that two trafficking pathways occur in wheat, with the proteins either being transported via the Golgi apparatus into the vacuole or accumulating directly within the lumen of the ER. They also suggest that the same individual protein could be trafficked by either pathway, possibly depending on the stage of development, and that segregation of gluten proteins both between and within protein bodies may occur.

Detailed Analysis of the Expression of an Alpha-gliadin Promoter and the Deposition of Alpha-gliadin Protein During Wheat Grain Development

Alpha-gliadin proteins are important for the industrial quality of bread wheat flour, but they also contain many epitopes that can trigger celiac (coeliac) disease (CD). The B-genome-encoded alpha-gliadin genes, however, contain very few epitopes. Controlling alpha-gliadin gene expression in wheat requires knowledge on the processes of expression and deposition of alpha-gliadin protein during wheat grain development. A 592-bp fragment of the promotor of a B-genome-encoded alpha-gliadin gene driving the expression of a GUS reporter gene was transformed into wheat. A large number of transgenic lines were used for data collection. GUS staining was used to determine GUS expression during wheat kernel development, and immunogold labelling and tissue printing followed by staining with an alpha-gliadin-specific antibody was used to detect alpha-gliadin protein deposited in developing wheat kernels. The promoter sequence was screened for regulatory motifs and compared to other available alpha-gliadin promoter sequences. GUS expression was detected primarily in the cells of the starchy endosperm, notably in the subaleurone layer but also in the aleurone layer. The alpha-gliadin promoter was active from 11 days after anthesis (DAA) until maturity, with an expression similar to that of a 326-bp low molecular weight (LMW) subunit gene promoter reported previously. An alpha-gliadin-specific antibody detected alpha-gliadin protein in protein bodies in the starchy endosperm and in the subaleurone layer but, in contrast to the promoter activity, no alpha-gliadin was detected in the aleurone cell layer. Sequence comparison showed differences in regulatory elements between the promoters of alpha-gliadin genes originating from different genomes (A and B) of bread wheat both in the region used here and upstream. The results suggest that additional regulator elements upstream of the promoter region used may specifically repress expression in the aleurone cell layer. Observed differences in expression regulator motifs between the alpha-gliadin genes on the different genomes (A and B) of bread wheat leads to a better understanding how alpha-gliadin expression can be controlled.

85: Venous Thromboembolism as the Initial Presentation of Primary Renal Amyloidosis

VENOUS THROMBOEMBOLISM AS THE INITIAL PRESENTATION OF PRIMARY RENAL AMYLOIDOSIS Mythili Ghanta , Sriranga L Bonam , Rajan Kapoor, Anjali Acharya Jacobi Medical Center, Bronx, New York, US Amyloidosis is a generic term that refers to the extracellular tissue deposition of fibrils composed of low molecular weight subunits of a variety of proteins. Primary or AL amyloid is due to deposition of protein derived from immunoglobulin light chain fragments. Hematologic manifestations associated with Amyloidosis, include anemia, thrombocytopenia and bleeding diathesis which may be seen in up to 44% of cases. Venous Thrombo Embolism (VTE) is a less well recognized complication. We report a 65 year old Hispanic female who presented with history of two episodes of idiopathic VTE and hypoalbuminemia. Her initial presentation was 2 years ago, with bilateral lower extremity (LE) swelling and pain which was due to deep venous thrombosis (DVT). Evaluation for a hypercoagulable state was negative. She was treated with Coumadin for 6 months. She presented again 6 months later, with right LE DVT and was restarted on Coumadin. At this time, she was noted to have a serum albumin of 2.5 gm/dl which was persistently low for 2 years duration and proteinuria of 5gm/day with a normal complete blood count, renal panel and echocardiogram. Serum protein electrophoresis showed a monoclonal spike in the alpha region. Renal biopsy revealed primary amyloidosis. Kappa: Lambda ratio was normal and urine light chain assay was negative. Bone marrow biopsy shows only 1% plasma cells. In a review of medical records of 2,132 patients with biopsy proven AL amyloidosis from Mayo clinic, they found that thromoembolic phenomena can antedate the diagnosis of amyloidosis. In a study published from Cleveland clinic the incidence of VTE in amyloidosis was up to 11% at 10 years, which was comparable to the incidence of VTE in multiple myeloma. Impairment of thrombin antithrombin pathway, in association with low antithrombin biological activity has been recognized to have possible pathogenic role in hypercoagulability of amyloidosis. This case illustrates that primary amyloidosis can be an underdiagnosed cause of VTE and Nephrotic syndrome should be considered in the differential diagnosis of unexplained VTE.

Wheat Gluten: High Molecular Weight Glutenin Subunits—Structure, Genetics, and Relation to Dough Elasticity

Gluten proteins, representing the major protein fraction of the starchy endosperm, are predominantly responsible for the unique position of wheat amongst cereals. These form a continuous proteinaceous matrix in the cells of the mature dry grain and form a continuous viscoelastic network during the mixing process of dough development. These viscoelastic properties underline the utilization of wheat to prepare bread and other wheat flour based foodstuffs. One group of gluten proteins is glutenin, which consists of high molecular weight (HMW) and low molecular weight (LMW) subunits. The HMW glutenin subunits (HMW-GS) are particularly important for determining dough elasticity. The common wheat possesses 3 to 5 HMW subunits encoded at the Glu-1 loci on the long arms of group 1 chromosomes (1A, 1B, and 1D). The presence of certain HMW subunits is positively correlated with good bread-making quality. Glutamine-rich repetitive sequences that comprise the central part of the HMW subunits are actually responsible for the elastic properties due to extensive arrays of interchain hydrogen bonds. Genetic engineering can be used to manipulate the amount and composition of the HMW subunits, leading to either increased dough strength or more drastic changes in gluten structure and properties.

Deletion of PsbM in Tobacco Alters the QB Site Properties and the Electron Flow within Photosystem II

Photosystem II, the oxygen-evolving complex of photosynthetic organisms, includes an intriguingly large number of low molecular weight polypeptides, including PsbM. Here we describe the first knock-out of psbM using a transplastomic, reverse genetics approach in a higher plant. Homoplastomic Delta psbM plants exhibit photoautotrophic growth. Biochemical, biophysical, and immunological analyses demonstrate that PsbM is not required for biogenesis of higher order photosystem II complexes. However, photosystem II is highly light-sensitive, and its activity is significantly decreased in Delta psbM, whereas kinetics of plastid protein synthesis, reassembly of photosystem II, and recovery of its activity are comparable with the wild type. Unlike wild type, phosphorylation of the reaction center proteins D1 and D2 is severely reduced, whereas the redox-controlled phosphorylation of photosystem II light-harvesting complex is reversely regulated in Delta psbM plants because of accumulation of reduced plastoquinone in the dark and a limited photosystem II-mediated electron transport in the light. Charge recombination in Delta psbM measured by thermoluminescence oscillations significantly differs from the 2/6 patterns in the wild type. A simulation program of thermoluminescence oscillations indicates a higher Q(B)/Q(-)(B) ratio in dark-adapted mutant thylakoids relative to the wild type. The interaction of the Q(A)/Q(B) sites estimated by shifts in the maximal thermoluminescence emission temperature of the Q band, induced by binding of different herbicides to the Q(B) site, is changed indicating alteration of the activation energy for back electron flow. We conclude that PsbM is primarily involved in the interaction of the redox components important for the electron flow within, outward, and backward to photosystem II.

PetG and PetN, but not PetL, are essential subunits of the cytochrome b6f complex from Synechocystis PCC 6803

The cytochrome b 6 f complex consists of four large core subunits and an additional four low molecular weight subunits, the function of which is elusive thus far. Here we sought to determine whether small subunits PetG, PetL, and PetN are essential for a cyanobacterial cytochrome b 6 f complex. We found that only PetL is dispensable, whereas PetG and PetN appear to be essential. Possible roles of the small cytochrome b 6 f complex subunits are discussed, and observations from our study are compared with previous findings.

MBET3 is required for the organization of the TRAPP complexes

Large tethering complexes mediate the initial interaction of a transport vesicle with its target membrane. There are two forms of the multi-subunit tethering complex called TRAPP (TRAPPI and TRAPPII) that tether transport vesicles in different trafficking steps. Understanding TRAPP complex assembly and the protein–protein interactions among the subunits is an important step in elucidating the function of this tether. Here we have used several different approaches to study the protein–protein interactions among the subunits of the TRAPP complexes in both mammalian cells and yeast. Our studies have revealed that the low molecular weight subunits of TRAPP form two subcomplexes in vitro. One subcomplex contains mammalian BET3 (mBET3), mTRS31 and mTRS20, while mBET5 and mTRS23 form a second subcomplex. Furthermore, mBET3 directly interacts with mBET5 in vitro. Our findings also suggest that the TRAPPII-specific subunit, yTrs120p (yeast Trs120p), binds to the periphery of the TRAPPII complex. Although the non-essential TRAPP subunit yTrs33p interacts with yBet3p, yTrs33p is not required for TRAPP complex assembly. Together our findings indicate that BET3 plays an important role in the organization of the TRAPP complexes in both mammalian cells and yeast.

Chemistry of gluten proteins

Gluten proteins play a key role in determining the unique baking quality of wheat by conferring water absorption capacity, cohesivity, viscosity and elasticity on dough. Gluten proteins can be divided into two main fractions according to their solubility in aqueous alcohols: the soluble gliadins and the insoluble glutenins. Both fractions consist of numerous, partially closely related protein components characterized by high glutamine and proline contents. Gliadins are mainly monomeric proteins with molecular weights (MWs) around 28,000–55,000 and can be classified according to their different primary structures into the α/ β-, γ- and ω-type. Disulphide bonds are either absent or present as intrachain crosslinks. The glutenin fraction comprises aggregated proteins linked by interchain disulphide bonds; they have a varying size ranging from about 500,000 to more than 10 million. After reduction of disulphide bonds, the resulting glutenin subunits show a solubility in aqueous alcohols similar to gliadins. Based on primary structure, glutenin subunits have been divided into the high-molecular-weight (HMW) subunits (MW=67,000–88,000) and low-molecular-weight (LMW) subunits (MW=32,000–35,000). Each gluten protein type consists or two or three different structural domains; one of them contains unique repetitive sequences rich in glutamine and proline. Native glutenins are composed of a backbone formed by HMW subunit polymers and of LMW subunit polymers branched off from HMW subunits. Non-covalent bonds such as hydrogen bonds, ionic bonds and hydrophobic bonds are important for the aggregation of gliadins and glutenins and implicate structure and physical properties of dough.

Analysis and validation of genome-specific DNA variations in 5′ flanking conserved sequences of wheat low-molecular-weight glutenin subunit genes

The thirty-three 5' flanking conserved sequences of the known low-molecular-weight subunit (LMW-GS) genes have been divided into eight clusters, which was in agreement with the classification based on the deduced N-terminal protein sequences. The DNA polymorphism between the eight clusters was obtained by sequence alignment, and a total of 34 polymorphic positions were observed in the approximately 200 bp regions, among which 18 polymorphic positions were candidate SNPs. Seven cluster-specific primer sets were designed for seven out of eight clusters containing cluster-specific bases, with which the genomic DNA of the ditelosomic lines of group 1 chromosomes of a wheat variety 'Chinese Spring' was employed to carry out chromosome assignment. The subsequent cloning and DNA sequencing of PCR fragments validated the sequences specificity of the 5' flanking conserved sequences between LMW-GS gene groups in different genomes. These results suggested that the coding and 5' flanking regions of LMW-GS genes are likely to have evolved in concerted fashion. The seven primer sets developed in this study could be used to isolate the complete ORFs of seven groups of LMW-GS genes, respectively, and therefore possess great value for further research in the contributions of a single LMW-GS gene to wheat quality in the complex genetic background and the efficient selections of quality-related components in breeding programs.

Modification of the Low Molecular Weight (LMW) Glutenin Composition of Transgenic Durum Wheat: Effects on Glutenin Polymer Size and Gluten Functionality

The low-molecular weight (LMW) glutenin subunits are major determinants of the viscoelasticity of durum wheat gluten, and therefore of its technological quality, with both quantitative effects and qualitative effects. We have modified the LMW glutenin subunit composition of the durum wheat cultivar Ofanto by expression of a transgene encoding a B-type LMW glutenin subunit and have carried out detailed analyses of two independent transformed lines in order to assess the effect of the transgene on the size distribution of the glutenin polymers and on their functional properties. In one line the expression of the transgene led to an increase in the amount of large glutenin polymers resulting in stronger and more stable dough. In the second line, however, the expression of the transgenic subunit was accompanied by decreased expression of endogenous LMW subunits with consequent detrimental effects on glutenin polymers and dough viscoelasticity. These results demonstrate that the LMW glutenin subunits contribute to the functional properties of wheat by influencing the amount and the distribution of glutenin polymers and indicate that either plant breeding or GM technology can be used to 'fine tune' the properties of durum wheat for different end uses by manipulating the amount and structures of individual LMW subunit proteins.

Relationship between glutenin subunit composition and gluten strength measurements in durum wheat

AbstractDurum breeders use a range of techniques in the development of new cultivars. An important selection criterion is the rheological properties of semolina dough and durum wheat breeders use this criterion in the development of new cultivars using a range of techniques. Because of the need to process large numbers of genotypes encountered in breeding programs, methods that are inexpensive, rapid, require small amounts of sample and that correlate with semolina quality are desirable. Using breeding material, this study investigated the relationship between the glutenin subunit composition and two traditional tests of gluten strength, gluten index (GI) and mixograph. Two sample sets of durum wheat breeding lines and cultivars, one grown in Canada (n = 229) and the other grown in Australia (n = 139) were analysed for GI, mixograph and both high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits by SDS‐PAGE. Nine different HMW and 14 different LMW allelic combinations were found. In the Canadian set, the most frequent LMW alleles were aaa, bba, caa and cfa while in the Australian set, caa was predominant. For the HMW subunits, the most common allelic groups were Glu‐A1c/Glu‐B1d (null, 6 + 8) and Glu‐A1c/Glu‐B1b (null, 7 + 8) with fewer numbers of Glu‐A1c/Glu‐B1e (null, 20) in both sample sets. LMW subunits were more important contributors to gluten strength than HMW subunits with the rank for higher GI according to the LMW allele (Canadian set) being caa = aaa &gt; bba and aaa &gt; cfa while HMW subunits 6 + 8 = 7 + 8 &gt; 20. Similarly, using the mixograph, strength ranking for the LMW alleles was aaa &gt; cfa = bba and HMW subunit 20 gave poorer rheological properties. For some samples with a good LMW allelic group a low GI was observed and vice versa. Further characterisation of the protein composition in these samples showed the GI results could be explained by polymeric/monomeric (P/M), glutenin/gliadin (Glu/Gli) and HMW/LMW ratios or the proportion of unextractable polymeric protein. © Crown in the right of the State of New South Wales, Australia; and for the Department of Agriculture and Agri‐Food, Government of Canada, © Minister of Public Works and Government Services Canada 2005. Published for SCI by John Wiley &amp; Sons, Ltd.

Influence of Mycotoxin Producing Fungi (Fusarium, Aspergillus, Penicillium) on Gluten Proteins during Suboptimal Storage of Wheat after Harvest and Competitive Interactions between Field and Storage Fungi

Cereals contaminated by Aspergillus spp., Penicillium spp., and Fusarium spp. and their mycotoxins, for example, ochratoxin A (OTA) and deoxynivalenol (DON), are not only a risk to human and animal health but can also show poor technological properties and baking quality. The influence of these genera on the sulfur speciation of low molecular weight (LMW) subunits of glutenin was characterized by investigating suboptimally stored wheat samples in situ by X-ray absorption near edge structure (XANES) spectroscopy and baking tests. Field fungi of the genus Fusarium have hardly any influence on both the sulfur speciation of wheat gluten proteins and the baking properties, whereas storage fungi of the genera Aspergillus and Penicillium have a direct influence. An increased amount of sulfur in sulfonic acid state was found, which is not available for thiol/disulfide exchange reactions in the gluten network, and thus leads to a considerably reduced baking volume. From changes of the composition of the mould flora during suboptimal storage of wheat and from the mycotoxin contents, it can be concluded that microbial competitive interactions play an important role in the development of the mould flora and the mycotoxin concentrations during (suboptimal) storage of wheat.