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At least 469 records · Page 26Linked to original sources
PubMed2002

Pasting properties of gamma-irradiated rice starches as affected by pH.

Changes in the viscosity properties of gamma-irradiated rice starches (from 1 to 25% amylose content) from four genotypes (JY293, Jiayu 293; XS, Xiushui; ZF504, Zhefu 504; and ZXN, Zaoxiannuo) during pasting in water (pH 7) or in different pH solutions were studied using a rapid visco analyzer. Peak viscosity (PV) of all native rice starches was little affected at pH 4 and 10, while hot paste viscosity (HPV) and cool paste (final) viscosity (CPV) were generally lower at pH 4 and higher at pH 10 as compared with that at pH 7. The PV, HPV, and CPV of gamma-irradiated starches were higher at pH 4 and lower at pH 10 than pH 7. All viscosity characteristics of native rice starches were reduced in stronger alkali (pH 11.5) or acidic (pH 2.5) solutions. However, the gamma-irradiated starches were substantially higher at pH 2.5 but lower at pH 11.5, indicating that the effect of irradiation was highly pH dependent. The swelling volume of irradiated ZF504 and JY293 starch at all irradiation levels was higher at pH 4 than pH 7, while the values were lowest at pH 2.5. The irradiated ZXN and XS starches had higher swelling volumes at pH 4 and pH 2.5 than pH 7. Differential scanning calorimetry analysis showed that gamma-irradiation caused progressively lower gelatinization peak temperature (T(p)) and higher gelatinization range (T(r)) at pH 7. T(p) was higher and T(r) was lower at a much stronger acidic condition (pH 1) for both native and irradiated starches. The possibility of using viscosity changes in low pH for the detection of irradiated starch was discussed.

Gamma Rays↗
PubMed2003

Partial beta-amylolysis retards starch retrogradation in rice products.

Starch retrogradation is the main cause of quality deterioration of starch-containing foods during storage. The current work investigated the effect of partial beta-amylolysis on the retrogradation of rice starch and the potential of beta-amylase in preparing rice products with extended shelf life. Isolated amylopectin, whole rice starch, and rice flour from a regular rice cultivar were partially hydrolyzed by either reagent-grade or food-grade beta-amylase. The degree of beta-amylolysis was expressed as average external chain length () for isolated amylopectin or the degree of hydrolysis (%) for other starch systems. Pulsed nuclear magnetic resonance was used to monitor starch retrogradation during storage at 4 degrees C. The results indicated that partial beta-amylolysis using reagent-grade beta-amylase retarded amylopectin retrogradation by shortening the of amylopectin. When was below DP 11.6, the amylopectin retrogradation was essentially inhibited. Partial beta-amylolysis had a similar effect on the amylopectin retrogradation in the whole starch system. The maltose produced in beta-amylolysis might slightly attenuate the retrogradation-retarding effect of partial beta-amylolysis. The effect of food-grade beta-amylase on starch retrogradation was also evident, although less effective than that of reagent-grade beta-amylase. The retrogradation-retarding effect of food-grade beta-amylase was also demonstrated in rice flour system, indicating a potential method for controlling the starch retrogradation of rice products.

Amylopectin↗
PubMed2003

Preparation of indigestible pyrodextrins from different starch sources.

Starch-modifying processes, such as pyrodextrinization, are potential ways to alter the nutritional features of this polysaccharide. A widely used method for pyrodextrinizing maize starch was also applied to lentil, sorghum, cocoyam, sagu, and cassava starches, and the in vitro digestibility of the products was evaluated. Pyrodextrins were produced by heating starch at 140 degrees C for 3 h, with catalytic amounts of HCl. The enzymatically available starch content of all preparations decreased by 55-65% after modification. Thus, pyrodextrinization seems to be an effective way to produce indigestible glucans from different starches. Pyrodextrins obtained were complex mixtures of starch derivatives with a wide range of molecular weight as estimated by gel filtration chromatography. Both their molecular weight profiles and contents of indigestible fractions varied with starch source. Experiments with lentil and cassava starches showed that changing dextrinization conditions also affects the susceptibility to enzymatic hydrolysis of the product.

Chemical Phenomena↗
PubMed2005

Determination of the molecular and structural characteristics of okenia, mango, and banana starches.

Starches were isolated from nonconventional sources (banana, mango, and okenia) and their characteristics were examined using polarized light microscopy, X-ray diffraction pattern, Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). Banana starch granules were of an ellipsoidal shape with size between approximately 8 and 20 microm; okenia had the smallest granule size, between approximately 2 and 5 microm. The three starches showed the Maltese cross, indicative of an intact granule structure. Okenia and mango starches had the A-type X-ray diffraction pattern, common to native cereal starches, whereas banana starch showed a mixture between A- and B-type pattern. Banana starch had the highest temperature (77.6 degrees C) and enthalpy (23.4 J/g) of gelatinization in excess water conditions; okenia had the lowest temperature (71.2 degrees C) and enthalpy (15 J/g), which may be related to the X-ray diffraction pattern and its small granule size. Both the okenia and mango starches had a higher molar mass and gyration radius than banana starch, which may be related to the differences determined in their crystalline structures.

Calorimetry, Differential Scanning↗
PubMed1990

Multi-enzyme electrodes for the determination of starch by flow injection.

A tri-enzyme electrode has been developed for determining starch in a flowing stream based on amperometric monitoring of hydrogen peroxide at a potential of +600 mV versus a silver--silver chloride reference electrode. The nylon-based starch-sensing membranes (over a platinum electrode) were prepared from an enzyme cocktail containing various ratios of amyloglucosidase (AMG), mutarotase (MUT) and glucose oxidase (GO). The best starch-sensing membrane (to give the type A electrode) was made from an enzyme cocktail of AMG--MUT--GO (2000 + 100 + 100 U; where 1 U = 16.67 nanokatals), i.e., containing a high level of AMG. In this system, starch samples were first incubated with soluble alpha-amylase (alpha-AMY) (1000 U) for 1 h at room temperature prior to analysis with the tri-enzyme electrode. Attempts were also made to immobilize alpha-AMY on to nylon net, either alone or as a component of a four-membrane starch-enzyme electrode but starch signals were weak compared with those generated by starch pre-treated with soluble alpha-AMY. This system, associated with the type A starch electrode, not only exhibited a calibration of wide linear range (1 x 10(-4)-0.1% m/v starch) but also showed promising operational properties. It has excellent thermal stability over the range 30-70 degrees C.

Electrodes↗
PubMed2001

Chain-length specificities of maize starch synthase I enzyme: studies of glucan affinity and catalytic properties.

It is widely known that some of the starch synthases and starch-branching enzymes are trapped inside the starch granule matrix during the course of starch deposition in amyloplasts. The objective of this study was to use maize SSI to further our understanding of the protein domains involved in starch granule entrapment and identify the chain-length specificities of the enzyme. Using affinity gel electrophoresis, we measured the dissociation constants of maize SSI and its truncated forms using various glucans. The enzyme has a high degree of specificity in terms of its substrate-enzyme dissociation constant, but has a greatly elevated affinity for increasing chain lengths of alpha-1, 4 glucans. Deletion of the N-terminal arm of SSI did not affect the Kd value. Further small deletions of either N- or C-terminal domains resulted in a complete loss of any measurable affinity for its substrate, suggesting that the starch-affinity domain of SSI is not discrete from the catalytic domain. Greater affinity was displayed for the amylopectin fraction of starch as compared to amylose, whereas glycogen revealed the lowest affinity. However, when the outer chain lengths (OCL) of glycogen were extended using the phosphorylase enzyme, we found an increase in affinity for SSI between an average OCL of 7 and 14, and then an apparently exponential increase to an average OCL of 21. On the other hand, the catalytic ability of SSI was reduced several-fold using these glucans with extended chain lengths as substrates, and most of the label from [14C]ADPG was incorporated into shorter chains of dp < 10. We conclude that the rate of catalysis of SSI enzyme decreases with the OCL of its glucan substrate, and it has a very high affinity for the longer glucan chains of dp approximately 20, rendering the enzyme catalytically incapable at longer chain lengths. Based on the observations in this study, we propose that during amylopectin synthesis shorter A and B1 chains are extended by SSI up to a critical chain length that soon becomes unsuitable for catalysis by SSI and hence cannot be elongated further by this enzyme. Instead, SSI is likely to become entrapped as a relatively inactive protein within the starch granule. Further glucan extension for continuation of amylopectin synthesis must require a handover to other SS enzymes which can extend the glucan chains further or for branching by branching enzymes. If this is correct, this proposal provides a biochemical basis to explain how the specificities of various SS enzymes determine and set the limitations on the length of A, B, C chains in the starch granule.

Amylopectin↗
PubMed2000

Amylase-resistant starch plus oral rehydration solution for cholera.

BACKGROUND: Although standard glucose-based oral rehydration therapy corrects the dehydration caused by cholera, it does not reduce the diarrhea. Short-chain fatty acids, which are produced in the colon from nonabsorbed carbohydrates, enhance sodium absorption. We conducted a study to determine the effects of an orally administered, nonabsorbed starch (i.e., one resistant to digestion by amylase) on fecal fluid loss and the duration of diarrhea in patients with cholera. METHODS: We randomly assigned 48 adolescents and adults with cholera to treatment with standard oral rehydration therapy (16 patients), standard therapy and 50 g of rice flour per liter of oral rehydration solution (16 patients), or standard therapy and 50 g of high-amylose maize starch, an amylase-resistant starch, per liter of oral rehydration solution (16 patients). The primary end points were fecal weight (for every 12-hour period during the first 48 hours after enrollment) and the length of time to the first formed stool. RESULTS: The mean (+/-SD) fecal weights in the periods 12 to 24 hours, 24 to 36 hours, and 36 to 48 hours after enrollment were significantly lower in the resistant-starch group (2206+/-1158 g, 1810+/-1018 g, and 985+/-668 g) than in the standard-therapy group (3251+/-766 g, 2621+/-1149 g, and 2498+/-1080 g; P=0.01, P= 0.04, and P=0.001, respectively). From 36 to 48 hours after enrollment, fecal weight was also significantly lower with the resistant-starch therapy than with the rice-flour therapy (985+/-668 g vs. 1790+/-866 g, P=0.01). The mean duration of diarrhea was significantly shorter with the resistant-starch therapy (56.7+/-18.6 hours) than with standard therapy alone (90.9+/-29.8 hours, P=0.001) or the rice-flour therapy (70.8+/-20.2 hours, P=0.05). Fecal excretion of starch was higher with the resistant-starch therapy (32.6+/-30.4) than with the standard therapy (11.7+/-4.1 g, P=0.002) or the rice-flour therapy (15.1+/-8.4 g, P=0.01). CONCLUSIONS: The addition of a resistant starch to oral rehydration solution reduces fecal fluid loss and shortens the duration of diarrhea in adolescents and adults with cholera.

Adolescent↗
PubMed2004

Most of ADP x glucose linked to starch biosynthesis occurs outside the chloroplast in source leaves.

Sucrose and starch are end products of two segregated gluconeogenic pathways, and their production takes place in the cytosol and chloroplast of green leaves, respectively. According to this view, the plastidial ADP.glucose (ADPG) pyrophosphorylase (AGP) is the sole enzyme catalyzing the synthesis of the starch precursor molecule ADPG. However, a growing body of evidences indicates that starch formation involves the import of cytosolic ADPG to the chloroplast. This evidence is consistent with the idea that synthesis of the ADPG linked to starch biosynthesis takes place in the cytosol by means of sucrose synthase, whereas AGP channels the glucose units derived from the starch breakdown. To test this hypothesis, we first investigated the subcellular localization of ADPG. Toward this end, we constructed transgenic potato plants that expressed the ADPG-cleaving adenosine diphosphate sugar pyrophosphatase (ASPP) from Escherichia coli either in the chloroplast or in the cytosol. Source leaves from plants expressing ASPP in the chloroplast exhibited reduced starch and normal ADPG content as compared with control plants. Most importantly however, leaves from plants expressing ASPP in the cytosol showed a large reduction of the levels of both ADPG and starch, whereas hexose phosphates increased as compared with control plants. No pleiotropic changes in photosynthetic parameters and maximum catalytic activities of enzymes closely linked to starch and sucrose metabolism could be detected in the leaves expressing ASPP in the cytosol. The overall results show that, essentially similar to cereal endosperms, most of the ADPG linked to starch biosynthesis in source leaves occurs in the cytosol.

Adenosine Diphosphate Glucose↗
PubMed1994

Effects of wheat-flour and oat mill fractions on jejunal flow, starch degradation and absorption of glucose over an isolated loop of jejunum in pigs.

The effect of cereal-based diets varying in dietary fibre (DF) on gastric emptying and glucose absorption over an isolated loop of jejunum was studied in four pigs fitted with two sets of re-entrant cannulas. The pigs were fed on either a wheat-flour diet or three diets based on oat flour (endosperm), rolled oats or oat bran containing different amounts of soluble DF. Mean transit time (MTT) of liquid estimated from the output from the first jejunal cannula was significantly higher with the two diets having the highest DF content, but MTT of dry matter (DM), starch, xylose and neutral non-starch polysaccharides (nNSP) was not correlated directly to the DF content of the diet. DF had a stimulatory effect on secretion of gastrointestinal juices, but the effect was not linearly correlated with the DF content of the diet. Starch was significantly degraded in digesta collected within 30 min after feeding with malto-oligosaccharides accounting for 140-147 g/kg total starch. The degradation was more extensive with higher DF and lower starch content of the diet. However, taking into account the differences in jejunal flow, the amount of malto-oligosaccharides available for absorption in the first 0.5 h decreased with higher levels of DF in the oat-based diets. The absorption of glucose from the isolated loop was 18-34 g/m intestine over an 8 h period with no significant differences between diets. This corresponded to a non-significant decrease in recovery of starch from 0.91 to 0.82 with increasing levels of DF and decreasing levels of starch in the diet. This suggests that the capacity for absorption of large doses of starch entering the proximal small intestine after ingestion of a carbohydrate-rich cereal-based diet has a major influence on the absorption at this site. Consequently any effect of DF on glucose absorption may be exerted either through the rate of gastric emptying or by impaired rate of absorption more distal in the small intestine and not by displacement of the site for starch absorption.

Animals↗
PubMed2001

Malabsorption of modified food starch (acetylated distarch phosphate) in normal infants and in 8-24-month-old toddlers with non-specific diarrhea, as influenced by sorbitol and fructose.

UNLABELLED: Acetylated distarch phosphate (ADiSP) is a modified starch used in some baby foods. The bioavailability of ADiSP and a native (unmodified) starch was evaluated in 20 normal infants and 21 toddlers aged 8-24 mo with chronic non-specific diarrhea. Formulae contained 8% native or 8% modified waxy maize starch. No infant or toddler consuming Formula N (native starch) had elevated peak breath hydrogen levels (20 ppm or greater), stools clinically positive for reducing substances (0.75% or greater) or loose stools. Fourteen infants received formula M (modified starch): 2 had elevated breath hydrogen, 1 had positive stools and another had loose stools. Of the 21 toddlers fed formula M, 2 had elevated breath hydrogen, but none had positive stools or loose stools. Formula NS (native starch with 2% sorbitol) had little effect on breath hydrogen in the infants but significantly increased it in the toddlers. Formula NS produced loose stools in 2 toddlers but no clinically positive stools in any infant or toddler. Formula MS (modified starch with 2% sorbitol) elevated breath hydrogen in 3 infants and 8 toddlers, and produced positive stools in 2 infants and 2 toddlers, and loose stools in 4 infants and 7 toddlers. Formula MSF (modified starch with 2% sorbitol and 5% fructose) elevated breath hydrogen in 7 infants and 10 toddlers, positive stools in 7 infants and 6 toddlers, and loose stools or diarrhea in 7 infants and 11 toddlers. CONCLUSION: ADiSP modified starch can increase breath hydrogen and produce loose stools. Sorbitol and fructose aggravate the malabsorption, in some cases leading to frank diarrhea.

Acetylation↗
PubMedDate not supplied

Chemical composition and starch digestibility of tortillas prepared with non-conventional commercial nixtamalized maize flours.

Non-conventional nixtamalized maize flours elaborated by a factory in Mexico were used for tortilla preparation. Tortillas were stored at 4 degrees C for up to 72 h and the total starch, available starch, resistant starch and retrograded resistant starch were assessed. The traditional white tortilla, used as a control, showed higher protein and fat contents than blue maize tortilla, whereas a maize-bean mixed tortilla had the highest protein, ash and fat contents. Lower total starch was obtained in the maize-bean tortilla than in white and blue maize tortillas. The available starch content in all tortillas decreased with the cold-storage, although the change was more marked for blue-maize tortillas. The maize-bean mixed tortillas exhibited the lowest in vitro digestibility, which is consistent with the relatively high resistant starch levels in the bean. Differences in resistant starch content were found between the two maize tortillas, which might be related to the softer texture of blue-maize tortilla. The starch digestibility features of these new types of nixtamalized maize flours open up the possibility of producing tortillas with variable nutritional properties.

Bread↗
PubMed1993

[Digestion, growth and body composition of carp (Cyprinus carpio L.) after feeding different starch varieties].

Maize starch (treatment I), pregelatinized maize starch (II), wheat starch (III), pregelatinized wheat starch (IV), potato starch (V) or manioc meal (VI) were mixed in portions of 41% (I-V) or 46.7% (VI) to a basal diet. Each experimental diet was fed to 33 carp (Cyprinus carpio L.) (three aquaria with 11 carp each) in a daily amount of 1.8-2.0% of live weight. The experiment lasted 118 days and the carp had a mean live weight of 146 g at the beginning. The diets I-IV had a similar, high energy digestibility of about 90%, whereas the diet with potato starch and the diet with manioc meal significantly lowered the digestibility of the energy to 85% or 87%. The growth and the feed expenditure were not influenced by the different starches. The carp had a mean final weight of 520 g. All carcasses had, on average, a content of ash, protein, fat and energy of 2.8%, 15.7%, 9.4% and 7.4 kJ per g fresh matter. However, potato starch and manioc meal distinctly reduced the energy retention in comparison to maize and wheat starch (diet I or III) because the contents of dry matter, fat and energy of the carcasses of these carp were significantly lowered.

Animal Feed↗
PubMed1996

[The effect of starch-rich single feed on the digestibility and the energy content of corn silage in cattle and sheep].

Different starch components were added to rations with maize silage measuring the influence of the supplements on the digestibility and energy content of maize silage in cattle (n = 36) and sheep (n = 36). The starch-rich components maize, wheat, barley, oat, cassava meal and potato starch were added to the total rations on average of 33%. All supplements were ground (sieve of 2.5 mm); additionally, wheat was added in extruded or crushed form. All rations including the control ration without starch components were supplemented with soybean meal to an average crude protein content of 12.4% DM. The mean starch content of the total rations was 42% DM. The supplementation of maize silage with the different starch components increased the digestibility of the organic matter of all rations on average only slightly from 77% to 78% in cattle, while the mean digestibility in sheep raised from 74% to 79% more pronounced. However, the influence of the different starch components on the digestibility was similar for both ruminants. The supplementation with the ground, crushed or extruded wheat, with barley and with oats impaired the digestibility of the crude fibre of the total ration and of the maize silage, respectively. Therefore, the digestibility of the organic matter of maize silage was reduced and the energy content decreased by about 6% in comparison to the control ration without starch supplementation. However, the supplementation with maize, cassava meal or potato starch had no negative effects on the digestibility and energy content of maize silage.

Animal Feed↗
PubMed2004

Starch-hemoglobin induces contraction on isolated rat aortic rings.

BACKGROUND: Blood substitutes are being developed using molecular solutions of modified free hemoglobin; however, anaphylactic reactions, severe renal toxicity, and hypertension have been reported in experimental models and human beings. Hypertension remains as an obstacle to the clinical use of most blood substitutes. Several investigators suggest that this effect is due to the interaction between nitric oxide and hemoglobin into the endothelial cells; hence, prevention of hemoglobin extravasation would avoid vasoconstriction. The forms of hemoglobin likely to prevent extravasation include polymerized and encapsulated Hb. Another alternative and significantly less expensive approach is the hydroxyethyl starch Hb-polymer. The aim of the present study was to compare the effect of hydroxyethyl-starch-hemoglobin with that of stroma-free hemoglobin on the in vitro contractile activity of aortic rings isolated from adult male rats. METHODS: The hemoglobin-based oxygen carrier was made using stroma-free hemoglobin prepared from outdated human red cells and conjugated with 10% hydroxyethyl starch 200-260 MW. The experiments were made in thoracic segments of the aortic rings incubated with hemoglobin, starch-hemoglobin or Ringer Krebs-Bicarbonate solution (RKB) during 30 min. Smooth muscle contraction with phenylephrine and subsequent inhibition of contraction with carbachol were performed before and after incubation with hemoglobin, starch-hemoglobin, or vehicle. RESULTS: Incubation with hemoglobin and starch-hemoglobin significantly increased the contractile response to phenylephrine of aortic rings compared with RKB solution. The maximal response to carbachol was significantly decreased in the aortic rings incubated with either hemoglobin or starch-hemoglobin in comparison with the RKB-incubated tissues. There were no differences between the aortic rings incubated with either hemoglobin, or starch-hemoglobin. CONCLUSIONS: These results show that there are no differences between the effects of stroma-free hemoglobin and starch-hemoglobin on the in vitro contractile activity of aortic rings isolated from adult male rats. Our findings do not support the hypothesis that an increase in the size of the hemoglobin molecule prevents hemoglobin extravasation, and the consequent vasoconstriction due to the scavenging of nitric oxide by stroma free hemoglobin in the cellular space between endothelium and smooth muscle.

Animals↗
PubMed1970

A study of sieve element starch using sequential enzymatic digestion and electron microscopy.

The fine structure of plastids and their starch deposits in differentiating sieve elements was studied in bean (Phaseolus vulgaris L.). Ultrastructural cytochemistry employing two carbohydrases specific for different linkages was then used to compare the chemical nature of "sieve tube starch" (the starch deposited in sieve elements) with that of the ordinary starch of other cell types. Hypocotyl tissue from seedlings was fixed in glutaraldehyde, postfixed in osmium tetroxide, and embedded in Epon-Araldite. Treatment of thin sections on uncoated copper grids with alpha-amylase or diastase at pH 6.8 to cleave alpha-(1 --> 4) bonds resulted in digestion of ordinary starch grains but not sieve element grains, as determined by electron microscopy. Since alpha-(1 --> 6) branch points in amylopectin-type starches make the adjacent alpha-(1 --> 4) linkages somewhat resistant to hydrolysis by alpha-amylase, other sections mounted on bare copper or gold grids were treated with pullulanase (a bacterial alpha-[1 --> 6] glucosidase) prior to digestion with diastase. Pullulanase did not digest sieve element starch, but rendered the starch digestible subsequently by alpha-amylase. Diastase followed by pullulanase did not result in digestion. The results provide evidence that sieve element starch is composed of highly branched molecules with numerous alpha-(1 --> 6) linkages.

Aldehydes↗
PubMed1998

Surface localization of zein storage proteins in starch granules from maize endosperm. Proteolytic removal by thermolysin and in vitro cross-linking of granule-associated polypeptides.

Starch granules from maize (Zea mays) contain a characteristic group of polypeptides that are tightly associated with the starch matrix (C. Mu-Forster, R. Huang, J.R. Powers, R.W. Harriman, M. Knight, G.W. Singletary, P.L. Keeling, B.P. Wasserman [1996] Plant Physiol 111: 821-829). Zeins comprise about 50% of the granule-associated proteins, and in this study their spatial distribution within the starch granule was determined. Proteolysis of starch granules at subgelatinization temperatures using the thermophilic protease thermolysin led to selective removal of the zeins, whereas granule-associated proteins of 32 kD or above, including the waxy protein, starch synthase I, and starch-branching enzyme IIb, remained refractory to proteolysis. Granule-associated proteins from maize are therefore composed of two distinct classes, the surface-localized zeins of 10 to 27 kD and the granule-intrinsic proteins of 32 kD or higher. The origin of surface-localized delta-zein was probed by comparing delta-zein levels of starch granules obtained from homogenized whole endosperm with granules isolated from amyloplasts. Starch granules from amyloplasts contained markedly lower levels of delta-zein relative to granules prepared from whole endosperm, thus indicating that delta-zein adheres to granule surfaces after disruption of the amyloplast envelope. Cross-linking experiments show that the zeins are deposited on the granule surface as aggregates. In contrast, the granule-intrinsic proteins are prone to covalent modification, but do not form intermolecular cross-links. We conclude that individual granule intrinsic proteins exist as monomers and are not deposited in the form of multimeric clusters within the starch matrix.

Amino Acid Sequence↗
PubMed2001

Tuber physiology and properties of starch from tubers of transgenic potato plants with altered plastidic adenylate transporter activity.

We showed recently that antisense plants with decreased activity of the plastidic ATP/ADP-transporter protein exhibit drastically reduced levels of starch and a decreased amylose/amylopectin ratio, whereas sense plants with increased activity of the transporter possessed more starch than wild-type plants and an increased amylose/amylopectin ratio. In this paper we investigate the effect of altered plastidic ATP/ADP-transporter protein expression on primary metabolism and granule morphology in more detail. Tuber tissues from antisense and sense plants exhibited substantially increased respiratory activity compared with the wild type. Tubers from antisense plants contained markedly increased levels of free sugars, UDP-Glc, and hexose phosphates, whereas phosphoenolpyruvate, isocitrate, ATP, ADP, AMP, UTP, UDP, and inorganic pyrophosphate levels were slightly decreased. In contrast, tubers from sense plants revealed a slight increase in adenine and uridine nucleotides and in the levels of inorganic pyrophosphate, whereas no significant changes in the levels of soluble sugars and metabolites were observed. Antisense tubers contained 50% reduced levels of ADP-Glc, whereas sense tubers contained up to 2-fold increased levels of this sole precursor for starch biosynthesis. Microscopic examination of starch grain morphology revealed that the size of starch grains from antisense tubers was substantially smaller (50%) compared with the wild type. The large starch grains from sense tubers appeared of a more angular morphology, which differed to the more ellipsoid shape of wild type grains. The results suggest a close interaction between plastidial adenylate transport and starch biosynthesis, indicating that ADP-Glc pyrophosphorylase is ATP-limited in vivo and that changes in ADP-Glc concentration determine starch yield, as well as granule morphology. Possible factors linking starch synthesis and respiration are discussed.

Adenine Nucleotides↗
PubMed1988

Do starch statoliths act as the gravisensors in cereal grass pulvini?

To determine if starch statoliths do, in fact, act as gravisensors in cereal grass shoots, starch was removed from the starch statoliths by placing 45-day-old intact barley plants (Hordeum vulgare cv 'Larker') in the dark at 25 degrees C for 5 days. Evidence from staining with I2-KI, scanning electron microscopy, and transmission electron microscopy indicated that starch grains were no longer present in plastids in the pulvini of plants placed in the dark for 5 days. Furthermore, gravitropic curvature response in these pulvini was reduced to zero, even though pulvini from vertically oriented plants were still capable of elongating in response to applied auxin plus gibberellic acid. However, when 0.1 molar sucrose was fed to the dark pretreated, starch statolith-free pulvini during gravistimulation in the dark, they not only reformed starch grains in the starch-depleted plastids in the pulvini, but they also showed an upward bending response. Starch grain reformation appeared to precede reappearance of the graviresponse in these sucrose-fed pulvini. These results strongly support the view that starch statoliths do indeed serve as the gravisensors in cereal grass shoots.

Darkness↗