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At least 631 records · Page 35Linked to original sources
PubMed2004

Plastidial alpha-glucan phosphorylase is not required for starch degradation in Arabidopsis leaves but has a role in the tolerance of abiotic stress.

To study the role of the plastidial alpha-glucan phosphorylase in starch metabolism in the leaves of Arabidopsis, two independent mutant lines containing T-DNA insertions within the phosphorylase gene were identified. Both insertions eliminate the activity of the plastidial alpha-glucan phosphorylase. Measurement of other enzymes of starch metabolism reveals only minor changes compared with the wild type. The loss of plastidial alpha-glucan phosphorylase does not cause a significant change in the total accumulation of starch during the day or its remobilization at night. Starch structure and composition are unaltered. However, mutant plants display lesions on their leaves that are not seen on wild-type plants, and mesophyll cells bordering the lesions accumulate high levels of starch. Lesion formation is abolished by growing plants under 100% humidity in still air, but subsequent transfer to circulating air with lower humidity causes extensive wilting in the mutant leaves. Wilted sectors die, causing large lesions that are bordered by starch-accumulating cells. Similar lesions are caused by the application of acute salt stress to mature plants. We conclude that plastidial phosphorylase is not required for the degradation of starch, but that it plays a role in the capacity of the leaf lamina to endure a transient water deficit.

Adaptation, Physiological↗
PubMed1999

Auxin and cytokinin have opposite effects on amyloplast development and the expression of starch synthesis genes in cultured bright yellow-2 tobacco cells.

In cultured Bright Yellow-2 (BY-2) tobacco (Nicotiana tabacum) cells, the depletion of auxin (2,4-dichlorophenoxyacetic acid) in the culture medium induces the accumulation of starch. This is accelerated by the addition of cytokinin (benzyladenine). Light and electron microscopic observations revealed that this amyloplast formation involves drastic changes in plastid morphology. The effects of auxin and cytokinin on amyloplast development were investigated by adding auxin or cytokinin to cells grown in a hormone-free culture. Auxin repressed amyloplast development, whereas cytokinin accelerated starch accumulation regardless of the timing of hormone addition. RNA gel-blot analysis revealed that the accumulation of the ADP-glucose pyrophosphorylase small subunit gene (AgpS), granule-bound starch synthase, and starch branching enzyme transcripts were also affected by hormonal conditions. High levels of AgpS, granule-bound starch synthase, and starch branching enzyme transcripts accumulated in amyloplast-developing cells grown in auxin-depleted conditions. Furthermore, the addition of auxin to the cells cultured in hormone-free medium reduced the level of AgpS transcripts, whereas the addition of cytokinin increased it, irrespective of the timing of hormone addition. These results suggest that auxin and cytokinin exert opposite effects on amyloplast development by regulating the expression of the genes required for starch biosynthesis.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1998

Characterization of dull1, a maize gene coding for a novel starch synthase.

The maize dull1 (du1) gene is a determinant of the structure of endosperm starch, and du1- mutations affect the activity of two enzymes involved in starch biosynthesis, starch synthase II (SSII) and starch branching enzyme IIa (SBEIIa). Six novel du1- mutations generated in Mutator-active plants were identified. A portion of the du1 locus was cloned by transposon tagging, and a nearly full-length Du1 cDNA sequence was determined. Du1 codes for a predicted 1674-residue protein, comprising one portion that is similar to SSIII of potato, as well as a large unique region. Du1 transcripts are present in the endosperm during the time of starch biosynthesis, but the mRNA was undetectable in leaf or root tissue. The predicted size of the Du1 gene product and its expression pattern are consistent with those of maize SSII. The Du1 gene product contains two repeated regions in its unique N terminus. One of these contains a sequence identical to a conserved segment of SBEs. We conclude that Du1 codes for a starch synthase, most likely SSII, and that secondary effects of du1- mutations, such as reduction of SBEIIa, result from the primary deficiency in this starch synthase.

Amino Acid Sequence↗
PubMed2006

Nature of the periplastidial pathway of starch synthesis in the cryptophyte Guillardia theta.

The nature of the periplastidial pathway of starch biosynthesis was investigated with the model cryptophyte Guillardia theta. The storage polysaccharide granules were shown to be composed of both amylose and amylopectin fractions with a chain length distribution and crystalline organization very similar to those of starch from green algae and land plants. Most starch granules displayed a shape consistent with biosynthesis occurring around the pyrenoid through the rhodoplast membranes. A protein with significant similarity to the amylose-synthesizing granule-bound starch synthase 1 from green plants was found as the major polypeptide bound to the polysaccharide matrix. N-terminal sequencing of the mature protein proved that the precursor protein carries a nonfunctional transit peptide in its bipartite topogenic signal sequence which is cleaved without yielding transport of the enzyme across the two inner plastid membranes. The enzyme was shown to display similar affinities for ADP and UDP-glucose, while the V(max) measured with UDP-glucose was twofold higher. The granule-bound starch synthase from Guillardia theta was demonstrated to be responsible for the synthesis of long glucan chains and therefore to be the functional equivalent of the amylose-synthesizing enzyme of green plants. Preliminary characterization of the starch pathway suggests that Guillardia theta utilizes a UDP-glucose-based pathway to synthesize starch.

Amino Acid Sequence↗
PubMed1982

Hydroxyethyl starch in priming fluid for cardiopulmonary bypass.

The physiochemical characteristics of hydroxyethyl starch make it suitable for use as a colloidal blood plasma substitute. In high doses, this drug may interfere with blood coagulation. Because of its effectiveness and low cost, we have used hydroxyethyl starch rather than albumin in the priming fluid for cardiopulmonary bypass: 500 ml of 6% hydroxyethyl starch and 2,000 ml of lactated Ringer's solution. To determine if excessive bleeding has been associated with the use of hydroxyethyl starch, we reviewed 760 cardiac operations. The patients were 49.9 +/- 0.5 years old (mean +/- SEM) and weighed 73 +/- 1 kg. Blood loss during the first postoperative day was 578 +/- 25 ml, and 4.0 +/- 0.2 units of bank blood were utilized in the perioperative period. We have used an improved method of administering heparin and protamine for the past 3 years. In the 461 patients operated upon since then, blood loss was 437 +/- 21 ml, 2.9 +/- 0.1 units of bank blood were used, and excessive postoperative bleeding necessitated re-exploration in nine patients (2.0%). These results compare favorably with other recently published series in which hydroxyethyl starch was not used in the pump prime. Thus the dose of hydroxyethyl starch in our priming fluid does not appear to be associated with excessive bleeding. In view of its safety and low cost, hydroxyethyl starch is a suitable colloidal blood plasma substitute for use during cardiopulmonary bypass.

Cardiopulmonary Bypass↗
PubMed2000

Effect of beta-cyclodextrin on pasting properties of wheat starch.

Changes of viscosity characteristics of genetically diverse hexaploid wheat starches during pasting in water, 1% NaCl solution, or at pH 4 or pH 10 were studied using a Rapid Visco-Analyzer. Peak viscosity (PV), hot paste viscosity (HPV) and cool paste viscosity (CPV) of all the wheat starches was little affected in pH 4 and pH 10 treatments. In 1% NaCl, all starches showed substantial increases in all three parameters relative to pasting in water. The use of 1% beta-cyclodextrin (beta-CD) (cycloheptaamylose) solution increased PV of high-swelling starches, but generally slightly decreased that of low swelling starches in all treatment conditions. HPV was always reduced by addition of 1% beta-CD, but CPV was increased in most treatments for Anza and Yecora Rojo (low swelling), but decreased for Klasic (high swelling). Bacterial alpha-amylase was added to starch or flour. The effect of beta-CD was shown to be independent of alpha-amylase inhibition in wheat starch, but beta-CD strongly inhibited alpha-amylase in wheat flour.

Cyclodextrins↗
PubMed2002

Food product models developed to evaluate starch as a food ingredient.

Three highly reproducible food models have been developed to evaluate rheological and functional properties of starches. The food models are dutch vla, dressing, and white sauce, and they vary in pH, serving temperature, oil content, and content of other functional ingredients than starch (milk proteins, whole egg, carrageenan). The viscous properties were calculated in a controlled stress rheometer, and the power law index, n, and the consistency index, K, was calculated. The viscoelastic properties at small deformations were measured by oscillating viscometry. Also a spreadability analysis was performed. The rheological data for the three food models were analysed by use of a principal component analysis (PCA), which enabled an evaluation of the functionality of the models and visualisation of the correlation to the concentration of starch. The rheological parameters all varied significantly with starch concentration in dutch vla. In dressing and white sauce most of the rheological parameters depended on the starch concentration. In addition, it was found that results from the empirical rheological method (USDA consistometer) correlate well with fundamental rheological parameters. Syneresis was measured for a period of time up to 15 days. The degree of syneresis of dressing was highly dependent on starch concentration, while the syneresis of the white sauce was dependent on time but not on starch concentration. The dutch vla showed no syneresis at all.

Dairy Products↗
PubMed1988

Utilization of milk proteins and cereal starches to obtain co-extrudates.

Extrusion of the cereal mixtures with 25% addition of milk proteins induced several changes in the chemical and physico-chemical properties of starch. Coefficient of expansion was close to the coefficient of natural cereal flours, but the extrudates were characterized by higher water absorption. Starch was only slightly dextrinized, but it contained more nitrogen compounds and mineral salts, and less free lipids. Solubility and swelling power of the extrudates did not change in a way characteristic for cereal starch and flours. Attention should be given to higher content of dietary fibre, pointing to the formation of the starch-lipids and the starch-protein complexes, less susceptible to enzymatic hydrolysis used. Hence, it can be stated that the latter increase was apparent only. It can be said that a mixture of cereal starch and milk proteins can be used to modify quality of the extruded products of increased protein content. More attention should be devoted to biochemical characteristics of the protein added, as this largely determines quality of the extruded starch-protein products.

Chemical Phenomena↗
PubMed1991

Starch as a renewable finish to improve the pesticide-protective properties of conventional workclothes.

Because many pesticide handlers persist in wearing and reusing conventional workclothes, a renewable functional finish that enhances the pesticide-protective qualities of fabrics would be useful. This study investigated the ability of starch to act as a pesticide trap, preventing transfer and increasing removal by laundering, and the effect of carboxymethyl cellulose on release of pesticide in laundry. The retention and distribution of methyl parathion (MeP) on 65% polyester/35% cotton fabric was studied with four finishes: starch and carboxymethyl cellulose (CMC) as nondurable finishes; durable press resin (DP) and durable press/carboxymethyl cellulose (DP/CMC) as durable finishes. Starching with an add-on of 8% (w/w) effectively reduced the area of contamination and enhanced the removal of methyl parathion from polyester/cotton fabrics. Residual pesticide values for CMC, DP, and DP/CMC finishes were similar to that of the unfinished fabric. While distribution profiles of methyl parathion throughout the yarn and fiber structures were similar for all the finishes, lower concentrations of pesticide were observed on the cotton fibers from the starched fabric. Starch reduced the pesticide transferring by rubbing from both 100% cotton and 65% polyester/cotton fabrics. These studies support the intriguing theory that starch can act as a pesticide trap on the fabric surface to decrease pesticide transfer and to enhance pesticide removal. Extensive penetration studies, field studies, and additional investigation of fiber, yarn, and fabric parameters are needed to further quantify the effects of starch.

Carboxymethylcellulose Sodium↗
PubMed1994

Effect of resistant starch on colonic fermentation, bile acid metabolism, and mucosal proliferation.

Resistant starch is by definition that part of starch that escapes digestion in the small bowel. Cecal fermentation of resistant starch into short-chain fatty acids will result subsequently in a decrease in pH. Thus, resistant starch may have the same effect on colonic luminal contents and mucosa as some fiber components. We studied the effects of adding 45 g native amylomaize (Hylon-VII) to a standardized diet in 14 healthy volunteers on fermentation and colonic mucosal proliferation. Hylon-VII is a high amylose maize starch, containing 62% resistant starch. During amylomaize consumption, breath hydrogen excretion rose 85% and fecal short chain fatty acid output increased 35% (P < 0.01). Excretion of primary bile acids increased and the soluble deoxycholic acid concentration decreased by 50% (P = 0.002). Subsequently, cytotoxicity of the aqueous phase of feces--as measured on a colon cancer cell line--decreased (P = 0.007). Colonic mucosal proliferation in rectal biopsies (proliferating cell nuclear antigen immunostaining) decreased from 6.7 to 5.4% (P = 0.05). We speculate that resistant starch consumption decreases colonic mucosal proliferation as a result of the decreased formation of cytotoxic secondary bile acids, which is possibly mediated through acidification of the large bowel by production of short-chain fatty acids.

Adult↗
PubMed2004

A comprehensive expression analysis of the starch synthase gene family in rice (Oryza sativa L.).

To elucidate the roles of the isogenes encoding starch synthase (EC 2.4.1.21) in rice (Oryza sativa L.), a comprehensive expression analysis of the gene family was conducted. Extensive searches for starch synthase genes were done in the databases of both the whole genome and full-length cDNAs of rice, and ten genes were revealed to comprise the starch synthase gene family. Multi-sequence alignment analysis of the starch synthase proteins from rice and other plant species suggested that they were grouped into five classes, soluble starch synthase I (SSI), SSII, SSIII, SSIV and granule-bound starch synthase (GBSS). In rice, there was one gene for SSI, three for SSII and two each for SSIII, IV and GBSS. The expression pattern of the ten genes in the developing caryopsis was examined by semi-quantitative RT-PCR analysis. Based on the temporal expression patterns, the ten genes could be divided into three groups: (i) early expressers ( SSII-2, III-1, GBSSII), which are expressed in the early stage of grain filling; (ii) late expressers ( SSII-3, III-2, GBSSI), which are expressed in the mid to later stage of grain filling; and (iii) steady expressers ( SSI, II-1, IV-1, IV-2), which are expressed relatively constantly during grain filling. Within a caryopsis, the three gene groups spatially share their expression, i.e. "early expressers" in the pericarp, the "late expressers" in the endosperm" and the "steady expressers" in both tissues. In addition, this grouping was reflected in the expression pattern of various rice tissues: expression in non-endosperm, endosperm or all tissues examined. The implications in this spatio-temporal work sharing of starch synthesis isogenes are discussed.

DNA Primers↗
PubMed1998

Compensation of decreased triose phosphate/phosphate translocator activity by accelerated starch turnover and glucose transport in transgenic tobacco.

Tobacco (Nicotiana tabacum L.) plants were transformed with an antisense construct of the chloroplast triose phosphate/phosphate translocator (TPT). Three transformant lines of the T4 progeny, which showed a large decrease in the transcript level of the TPT were used for further biochemical and physiological characterisation. In all antisense lines tested, TPT transport activity was diminished by 50-70% compared with the wild type (WT). Despite this high reduction in the transport capacity, alpha TPT plants lacked any visible phenotype. Hexokinase and alpha-amylase activities were increased in alpha TPT plants compared with the WT, whereas activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and ADP-glucose pyrophosphorylase (AGPase) were not affected. At the end of a 14-h light period, leaf starch contents in alpha TPT lines were similar to those of the WT and controls, indicating that a decrease in the TPT had no effect on starch accumulation. Sucrose contents were diminished by more than 50% in alpha TPT lines compared with control plants. The time course of starch accumulation revealed a transient increase in the starch content in a selected alpha TPT line after 6 h in the light, followed by a decrease towards the end of the light period. Labelling with 14C indicated that during the dark and light (late afternoon) periods starch is mobilised at higher rates in alpha TPT lines than in the controls. Glucose/fructose ratios at the end of the dark period were increased from 1.2 in control plants to 2 in alpha TPT lines indicating increased amylolytic starch degradation. Initial rates of [14C] glucose transport in isolated chloroplasts were increased by a factor of 2-3 in alpha TPT plants compared with the WT. Rates of CO2 assimilation were substantially diminished in the alpha TPT lines in high CO2 and low O2, but remained unaffected in ambient CO2. The rate of photosynthetic electron transport during the induction of photosynthesis in saturating CO2 exhibited pronounced oscillations only in WT and control plants. Oscillations were less pronounced in alpha TPT plants, indicating that phosphate limitation of photosynthesis is lowered in alpha TPT plants compared with the WT. It is proposed that photoassimilates are more readily directed into starch biosynthesis in alpha TPT plants. This is supported by determinations of 3-phosphoglycerate levels (an activator of AGPase) during the transition from dark to light in high CO2.

Amino Acids↗
PubMed1999

Purification and characterisation of a novel starch synthase selective for uridine 5'-diphosphate glucose from the red alga Gracilaria tenuistipitata.

Red algae (Rhodophyceae) are photosynthetic eukaryotes that accumulate starch granules in the cytosol. Starch synthase activity in crude extracts of Gracilaria tenuistipitata Chang et Xia was almost 9-fold higher with UDP[U-14C]glucose than with ADP[U-14C]glucose. The activity with UDP[U-14C]glucose was sensitive to proteolytic and oxidative inhibition during extraction whilst the activity with ADP[U-14C]glucose appeared unaffected. This indicates the presence of separate starch synthases with different substrate specificities in G. tenuistipitata. The UDPglucose: starch synthase was purified and characterised. The enzyme appears to be a homotetramer with a native M(r) of 580 kDa and displays kinetic properties similar to other alpha-glucan synthases such as stimulation by citrate, product (UDP) inhibition and broad primer specificity. We propose that this enzyme is involved in cytosolic starch synthesis in red algae and thus is the first starch synthase described that utilises UDPglucose in vivo. The biochemical implications of the different compartmentalisation of starch synthesis in red algae and green algae/plants are also discussed.

Kinetics↗
PubMed2004

Physicochemical properties of cissus gum powder extracted with the aid of edible starches.

Gum powder was extracted from the stem and root of the cissus (Cissus populnea Guill and perr Ampelidacae) plant using water. Extraction was facilitated by the incorporation of 25-50% edible starches of sweet cassava, sweet potato, and maize. Dry samples were milled and sieved through a 250-microm sieve. Proximate and physicochemical properties of the gum samples were determined using standard methods. Results of the proximate analyses showed that protein and ash contents of the root gum were appreciably higher than those of the stem gum. Values of the crude fiber and ether extract of the root gum were lower than those of the stem gum. Inclusion of edible starches in the extraction process appreciably lowered proximate values. Results of the physicochemical properties showed that cissus gum samples did not form true gel but a "putty-like" mass. Addition of starches at various levels did not alter the characteristic putty-like nature of the gum. The gum samples had a remarkably low oil absorption capacity. Cissus gum samples had appreciably higher emulsion capacity and stability than the samples containing starch. The pH of the cissus gum powder and those of the starch-containing samples lie in the low-acid range (5.69-6.49). Cissus gum samples were highly hygroscopic; however, the addition of starch lowered the hygroscopicity. Incorporation of 25% starch into cissus mucilage enhanced extraction of the gum without adverse alteration of the physicochemical properties.

Chemical Phenomena↗
PubMed2001

Low density lipoprotein receptor mRNA in rat liver is affected by resistant starch of beans.

The effects of resistant starches of beans on serum cholesterol and hepatic low density lipoprotein (LDL) receptor mRNA in rats were investigated. Rats were fed a cholesterol-free diet with 150 g/kg corn starch (CS), 150 g/kg adzuki (Vigna angularis) starch (AS), 150 g/kg kintoki (Phaseolus vulgaris, variety) starch (KS), or 150 g/kg tebou (P. vulgaris, variety) starch (TS) for 4 wk. There were no significant differences in body weight among groups through the experimental period. The liver weight in the CS group was 1.1-1.2 times higher than that in the AS, KS, and TS groups. The cecum weight in the TS was 1.4 times higher than that in the CS group, and the cecal pH in the CS group was significantly higher than in the other groups. The serum total cholesterol, very low density lipoprotein + intermediate density lipoprotein + LDL-cholesterol and high density lipoprotein (HDL)-cholesterol concentrations in the bean starch groups were significantly lower than those in the CS group through the feeding period. The total cholesterol/HDL-cholesterol ratio in the bean starch groups was also significantly lower than that in the CS group at the end of the 4-wk feeding period. The hepatic cholesterol concentration in the TS group was significantly higher than in the CS group at the end of the 4-wk feeding period. The relative quantity of hepatic apo B mRNA in the AS group was 1.2 times higher than that in the CS group, and the hepatic LDL receptor mRNA levels in the AS and TS groups were 1.8-2.0 times higher than that in the CS group. The results of this study demonstrate that AS, KS, and TS lowered the serum total cholesterol level by enhancing the hepatic LDL receptor mRNA level.

Animals↗
PubMed1991

Thresholds for starch and Polycose are lower than for sucrose in rats.

Detection thresholds for corn starch, Polycose and sucrose in water were assessed by a new technique. Rats were trained to avoid these carbohydrates by giving them fluid containing carbohydrate mixed with lithium chloride on some days, and fluid containing sodium chloride with no carbohydrate on other days. Rats trained by this procedure avoided the substance that they were trained to avoid, but did not avoid other substances. Thus rats trained to avoid starch avoided mixtures containing as little as 0.025% starch, but did not avoid Polycose, sucrose or sodium chloride. Rats trained to avoid Polycose avoided fluids containing as little as 0.01% Polycose, but did not avoid fluids containing starch or sucrose. Finally, rats trained to avoid sucrose avoided fluids containing as little as 0.05% sucrose, but did not avoid fluids containing starch or Polycose. Therefore, rats possess a keen sensitivity for starch, a substance that is commonly thought to be tasteless. Furthermore, starch, Polycose and sucrose are discriminable from each other.

Animals↗
PubMed2003

Physical investigations of surface membrane-water relationship of intact and gelatinized wheat-starch systems.

Water mobility in intact and dried gelatinized starch was investigated by gravimetric water sorption, scanning electron microscopy (SEM), and solid-state nuclear magnetic resonance (NMR). A multi-component exponential model quantitatively measured different spin-spin relaxation times of two water components, namely bound water (Tsi) at 3.16 ms and mobile or free water (Tsii) at 3.23 ms, as a function of water activity (aw). The starch samples were moistened to 30% moisture content. SEM confirmed the disrupted, absorbent microstructure in dried, gelatinized starch powder and revealed starch granules in an incomplete gelatinized state, as compared to the complete membrane surface of the intact starch granule. Starch granules sorbed significantly differently at low aw, but after aw=0.44, sorption leveled similarly with increasing aw. The presence and role of a surface membrane was concluded, in support of the hypothetical "water sink" properties of intact granules, and was considered to influence in part the sorption behavior of incompletely gelatinized starch granules.

Adsorption↗
PubMed2006

A cell signal from the coral Plesiastrea versipora reduces starch synthesis in its symbiotic alga, Symbiodinium sp.

We have previously shown that the coral cell signal, host release factor (HRF) from the scleractinian coral Plesiastrea versipora (Lamarck) stimulates the release of glycerol from its symbiotic dinoflagellate, Symbiodinium sp. Glycerol is a precursor for algal triacylglycerol (TG) and starch, and we have previously observed that HRF reduces the amount of newly synthesized TG in Symbiodinium sp. We have now examined the effect of P. versipora HRF on starch synthesis in isolated Symbiodinium. HRF had no effect on starch synthesis after 2 h photosynthesis (16.3+/-3.0 microg starch per 10(6) algae) compared with algae in seawater (13.9+/-1.2 microg starch per 10(6) algae). However, after 4 h incubation in HRF, there was a reduction (0-76%), in the amount of newly synthesized starch which was correlated with the amount of HRF (10-76 microg/ml). Reducing algal synthesis of both TG and starch in parallel with stimulating glycerol release may provide a mechanism to regulate the population density of intracellular symbiotic algae while still ensuring the transfer of photosynthetically fixed carbon to the animal host in the form of glycerol.

Animals↗