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At least 1,171 records · Page 65Linked to original sources
PubMed1981

Photosynthate Partitioning into Starch in Soybean Leaves: II. IRRADIANCE LEVEL AND DAILY PHOTOSYNTHETIC PERIOD DURATION EFFECTS.

Two photosynthetic periods and photosynthetic photon flux densities (PPFD) were used to study the relationship between the rate of photosynthesis and starch accumulation in vegetative soybean leaves (Merr. cv Amsoy 71). Plants grown in short daily photosynthetic periods (7 hours) had higher rates of CO(2) fixation per unit leaf dry weight and of leaf starch accumulation than plants grown in long daily photosynthetic periods (14 hours) irrespective of PPFD. CO(2) fixation rates per unit leaf area were similar in 7-hour and 14-hour plants grown at low PPFD but were highest in 14-hour plants at the high PPFD. When single leaves of 14-hour plants were given 7-hour photosynthetic periods, their rates of starch accumulation remained unchanged. The programming of starch accumulation rate and possibly of photosynthetic rate by the length of the daily photosynthetic period is apparently a whole-plant, not an individual leaf, phenomenon. Programming of chloroplast starch accumulation rate by length of the daily photosynthetic and/or dark periods was independent of PPFD within the ranges used in this experiment.

Journal Article↗
PubMed1984

Effect of N-source on soybean leaf sucrose phosphate synthase, starch formation, and whole plant growth.

Soybeans (Glycine max L. Merr. cv Tracy and Ransom) were grown under N(2)-dependent or NO(3) (-)-supplied conditions, and the partitioning of photosynthate and dry matter was characterized. Although no treatment effects on photosynthetic rates were observed, NO(3) (-)-supplied plants in both cultivars had lower starch accumulation rates than N(2)-dependent plants. Leaf extracts of NO(3) (-)-supplied plants had higher activities of sucrose phosphate synthase (SPS) and cytoplasmic fructose-1,6-bisphosphatase (FBPase) than N(2)-dependent plants. The variation in starch accumulation was correlated negatively with the activity of SPS, but not the activity of FBPase, UDP-glucose pyrophosphorylase, or ADP-glucose pyrophosphorylase. These results suggested that starch accumulation is biochemically controlled, in part, by the activity of SPS. Leaf starch content at the beginning of the photoperiod was lower in NO(3) (-)-supplied plants than N(2)-dependent plants in both cultivars which suggested that net starch utilization as well as accumulation was affected by N source.Total dry matter accumulation and dry matter distribution was affected by N source in both cultivars, but the cultivars differed in how dry matter was partitioned between the shoot and root as well as within the shoot. The activity of SPS was correlated positively with total dry matter accumulation which suggested that SPS activity is related to plant growth rate. The results suggested that photosynthate partitioning is an important but not an exclusive factor which determines whole plant dry matter distribution.

Journal Article↗
PubMed1984

Control of Photosynthetic Sucrose Synthesis by Fructose 2,6-Bisphosphate : II. Partitioning between Sucrose and Starch.

The role of fructose 2,6 bisphosphate in partitioning of photosynthate between sucrose and starch has been studied in spinach (Spinacia oleracea U.S. hybrid 424). Spinach leaf material was pretreated to alter the sucrose content, so that the rate of starch synthesis could be varied. The level of fructose 2,6-bisphosphate and other metabolites was then related to the accumulation of sucrose and the rate of starch synthesis. The results show that fructose 2,6-bisphosphate is involved in a sequence of events which provide a fine control of sucrose synthesis so that more photosynthate is diverted into starch in conditions when sucrose has accumulated to high levels in the leaf tissue. (a) As sucrose levels in the leaf rise, there is an accumulation of triose phosphates and hexose phosphates, implying an inhibition of sucrose phosphate synthase and cytosolic fructose 1,6-bisphosphatase. (b) In these conditions, fructose 2,6-bisphosphate increases. (c) The increased fructose 2,6-bisphosphate can be accounted for by the increased fructose 6-phosphate in the leaf. (d) Fructose 2,6-bisphosphate inhibits the cytosolic fructose 1,6-bisphosphatase so more photosynthate is retained in the chloroplast, and converted to starch.

Journal Article↗
PubMed1985

Starch Branching Enzymes from Maize : Immunological Characterization using Polyclonal and Monoclonal Antibodies.

Spleen cells from mice immunized with starch branching enzymes were fused with cells from the mouse myeloma Sp2/0-AG14 cell line to form hybridomas. Those hybridomas producing antibodies against the branching enzyme were screened by the enzyme-linked immunosorbent assay using purified branching enzyme as the antigen. Three monoclonal cell lines (1A1D7, 1A1C3 and 4D2A9D8) were found to produce antibodies which showed positive enzyme-linked immunosorbent assay reactions with maize branching enzyme I in addition to branching enzymes IIa and IIb. Three other monoclonal cell lines (4D2D10, 4D2F9, and 2A6C12) were also selected which were found to produce antibodies showing positive enzyme-linked immunosorbent assay reactions with branching enzymes IIa and IIb only.Amino acid composition and peptide maps obtained after trypsin or chymotrypsin digestion show that there is no difference between branching enzyme IIa and IIb but they are significantly different from branching enzyme I which, along with immunological data, suggests that only two forms of starch branching enzyme may be present in maize kernels.Immunological cross-reaction was also found between the starch branching enzyme from maize kernels and the glycogen branching enzyme from Escherichia coli using polyclonal antibodies against starch branching enzyme I or IIa and IIb or E. coli glycogen branching enzyme, suggesting some immunological similarities between maize starch branching enzymes and E. coli glycogen branching enzyme.

Journal Article↗
PubMed1985

Sucrose and Starch Synthesis in Spinach Plants Grown under Long and Short Photosynthetic Periods.

The flow of carbon into sucrose and starch was investigated in fully expanded primary leaves of spinach using the long to short day transition and partial defoliation as tools to manipulate sucrose/starch synthesis. Transfer from 12 hour to 7 hour photosynthetic periods resulted in a 4-fold increase in the initial rate of starch synthesis, a 50% increase in the initial rate of sucrose synthesis, a 30% increase in leaf sucrose, and a 40% decrease in fructose, 2,6-biphosphate. In addition, sucrose synthesis rates in cells isolated from shortened daylength plants are 80% higher than in cells isolated from control plants. These results show that, in spinach, an increase in the rates of both sucrose and starch synthesis can occur under short day conditions. In contrast, when short day plants are partially defoliated, starch levels remain high, fructose 2,6-biphosphate levels remain low, but the level of leaf sucrose drops by 50%. Thus, when demand exceeds supply, starch synthesis has priority over filling of leaf sucrose pools in the short day plant.

Journal Article↗
PubMed1986

Identification of granule-bound starch synthase in potato tubers.

Starch granules isolated from potato (Solanum tuberosum L.) tubers were extracted with sodium dodecyl sulfate and the extract was analyzed. A major protein with a molecular weight of 60,000 daltons was detected. This protein was purified by preparative sodium dodecyl sulfate-gel electrophoresis and specific antibodies were prepared. The anti-60-kilodalton antibodies obtained (a) cross-reacted with the waxy proteins of both maize (Zea mays L.) and grain amaranth (Amaranthus hypochondriacus L.), and (b) inhibited starch synthase activity in partially digested starch granules of the grain amaranth. This evidence strongly suggests that the major 60-kilodalton protein present in potato starch granules represents the granule-bound starch synthase.

Journal Article↗
PubMed1990

Degradation of Native Starch Granules by Barley alpha-Glucosidases.

The initial hydrolysis of native (unboiled) starch granules in germinating cereal kernels is considered to be due to alpha-amylases. We report that barley (Hordeum vulgare L.) seed alpha-glucosidases (EC 3.2.1.20) can hydrolyze native starch granules isolated from barley kernels and can do so at rates comparable to those of the predominant alpha-amylase isozymes. Two alpha-glucosidase charge isoforms were used individually and in combination with purified barley alpha-amylases to study in vitro starch digestion. Dramatic synergism, as much as 10.7-fold, of native starch granule hydrolysis, as determined by reducing sugar production, occurred when high pl alpha-glucosidase was combined with either high or low pl alpha-amylase. Synergism was also found when low pl alpha-glucosidase was combined with alpha-amylases. Scanning electron micrographs revealed that starch granule degradation by alpha-amylases alone occurred specifically at the equatorial grooves of lenticular granules. Granules hydrolyzed by combinations of alpha-glucosidases and alpha-amylases exhibited larger and more numerous holes on granule surfaces than did those granules attacked by alpha-amylase alone. As the presence of alpha-glucosidases resulted in more areas being susceptible to hydrolysis, we propose that this synergism is due, in part, to the ability of the alpha-glucosidases to hydrolyze glucosidic bonds other than alpha-1,4- and alpha-1,6- that are present at the granule surface, thereby eliminating bonds which were barriers to hydrolysis by alpha-amylases. Since both alpha-glucosidase and alpha-amylase are synthesized in aleurone cells during germination and secreted to the endosperm, the synergism documented here may function in vivo as well as in vitro.

Journal Article↗
PubMed1992

Phosphorus Nutrition Influence on Starch and Sucrose Accumulation, and Activities of ADP-Glucose Pyrophosphorylase and Sucrose-Phosphate Synthase during the Grain Filling Period in Soybean.

Several lines of evidence indicate that the partitioning of photosynthate between starch and sucrose is influenced by the relative concentrations of inorganic phosphate (Pi) in the cytosol and chloroplast. Two greenhouse experiments were conducted to determine the influence of long-term differences in soil P levels, ranging from deficient to supraoptimum, on leaf starch and sucrose concentrations, and activities of adenosine diphosphate glucose (ADPG) pyrophosphorylase and sucrose-phosphate synthase (SPS) during the grain filling period in soybean (Glycine max [L.] Merr.). It was hypothesized that, compared with optimum P nutrition, leaf starch and sucrose concentrations would be increased and decreased, respectively, for P deficiency and visa versa for supraoptimum P nutrition. Relative to the optimum soil P level, leaf Pi concentration was not altered by P deficiency but was increased two- to fourfold for the supraoptimum soil P treatment. The concentrations of leaf starch and sucrose were not markedly affected by any of the P fertility treatments and were not closely related to the activities of ADPG pyrophosphorylase and SPS. P deficiency resulted in increased activity of both enzymes in one of the experiments. The results indicated that long-term soil P treatments, that caused either large decreases in plant growth (P deficiency) or large increases in leaf Pi concentration (supraoptimum P), did not markedly alter starch and sucrose metabolism. Furthermore, it can be inferred that the method of plant culture and/or imposition of the P treatments is a critical factor in interpreting results of P nutrition studies.

Journal Article↗
PubMed1992

Alterations in Carbohydrate Intermediates in the Endosperm of Starch-Deficient Maize (Zea mays L.) Genotypes.

Metabolite levels in kernels of selected starch-deficient mutants of maize (Zea mays L.) were investigated to gain insight into partitioning of carbohydrate metabolism during kernel development. Several free sugars, hexose phosphates, triose phosphates, fructose-2,6-bisphosphate, and pyrophosphate were measured in normal, shrunken, shrunken-2, amylose extender dull waxy, and brittle genotypes, which were in a near-isogenic W64A background. These mutants were selected to include at least one lesion in both the cytosolic (shrunken) and amyloplastic (shrunken-2) compartments. All the starch-deficient genotypes contained elevated levels of fructose-2,6-bisphosphate and triose phosphates but reduced levels of pyrophosphate, indicating an enhanced glycolytic utilization of carbohydrates in response to the reduced utilization of sugars for starch synthesis. The shrunken kernels (sucrose synthase deficient) contained reduced levels of glucose-1-phosphate, glucose-6-phosphate, and fructose-6-phosphate, and this reduction paralleled the reduction in starch accumulation, but levels of triose phosphates were elevated. In shrunken-2 kernels, glucose-1-phosphate, glucose-6-phosphate, and fructose-6-phosphate, dihydroxyacetone phosphate, and glyceraldehyde-3-phosphate were increased, but fructose-1,6-bisphosphate was lower. These findings support the view that hexose phosphate transport across the amyloplast envelope is more important for starch biosynthesis than transport of triose phosphates. The amylose extender dull waxy mutation showed less dramatic effects on hexose phosphates, but the triose phosphates were greatly increased. The brittle mutation, which has an unknown lesion, showed distinctly similar changes in metabolite levels with shrunken-2, suggesting that the lesion may be associated with the amyloplast.

Journal Article↗
PubMed1996

Preamylopectin Processing: A Mandatory Step for Starch Biosynthesis in Plants.

It has been generally assumed that the [alpha]-(1->4)-linked and [alpha]-(1->6)-branched glucans of starch are generated by the coordinated action of elongation (starch synthases) and branching enzymes. We have identified a novel Chlamydomonas locus (STA7) that when defective leads to a wipeout of starch and its replacement by a small amount of glycogen-like material. Our efforts to understand the enzymological basis of this phenotype have led us to determine the selective disappearance of an 88-kD starch hydrolytic activity. We further demonstrate that this enzyme is a debranching enzyme. Cleavage of the [alpha]-(1->6) linkage in a branched precursor of amylopectin (preamylopectin) has provided us with the ground rules for understanding starch biosynthesis in plants. Therefore, we propose that amylopectin clusters are synthesized by a discontinuous mechanism involving a highly specific glucan trimming mechanism.

Journal Article↗
PubMed1994

Degradation of Raw Starch by a Wild Amylolytic Strain of Lactobacillus plantarum.

Lactobacillus plantarum A6, isolated from fermented cassava, can break down cassava raw starch that has not been subjected to preliminary physicochemical treatment. When the pH was kept at 6, the microorganism cultured in a bioreactor excreted a high alpha-amylase activity (60 U/ml). Synthesis of the enzyme occurred during the stationary phase and resulted in full hydrolysis of the cassava starch granules. This gave 41 g of lactic acid from 45 g of raw starch after 3 days of fermentation. Enzymatic attack was evident under scanning electron microscopy in the rougher appearance of the surface of starch granules and in the presence of large cavities in some of them. In contrast, when the pH was not regulated, only a small amount of alpha-amylase activity was produced (2 U/ml) and no decrease in the starch content of the medium was observed. However, under scanning electron microscopy, some granules displayed a rougher surface, which might have been the result of weak enzymatic attack.

Journal Article↗
PubMed1998

Effect of processing on some properties of cowpea (Vigna unguiculata), seed, protein, starch, flour and akara.

Large brown eye Kano white cowpea (Vigna unguiculata) seeds were processed into three batches of flour by wetting, drying individually at 30, 80, and 120 degrees C, decorticating and dry milling. Starch was extracted from the cowpea seed and protein from the flour using water as solvent. The water-extractable proteins were purified by dialysis and analysed by electrophoresis. The cowpea flour was used to produce akara balls (fried paste). The microstructure of the cowpea cotyledon, flour, starch and akara crumb were examined with a scanning electron microscope (SEM). Electrophoretic separation revealed that some of the protein fractions from the sample extracted from 30 degrees C dried cowpea were absent in the sample extracted from the 80 degrees C and 120 degrees C dried cowpeas or their quantities had decreased. In the SEM study, no difference was observed in the microstructure of the three flour samples except in the size and shape of the starch granules and particles of protein and cell wall material. The starch granules from the cowpea dried at 120 degrees C had surface defects. Cavities occurred in the cotyledons of the 80 and 120 degrees C dried cowpea seeds, some starch granules, protein matrix and sometimes the entire cell contents were lost from the cell. The protein sheet in the akara crumb became thicker as temperature increased to 80 and 120 degrees C.

Dietary Carbohydrates↗
PubMed2002

Activity and expression of banana starch phosphorylases during fruit development and ripening.

Two main forms of starch phosphorylase (EC 2.4.1.1) were identified and purified from banana (Musa acuminata Colla. cv. Nanicão) fruit. One of them, designated phosphorylase I, had a native molecular weight of 155 kDa and subunit of 90 kDa, a high affinity towards branched glucans and an isoelectric point around 5.0. The other, phosphorylase II, eluted at a higher salt concentration from the anion exchanger, had a low affinity towards branched glucans, a native molecular weight of 290 kDa and subunit of 112 kDa. Kinetic studies showed that both forms had typical hyperbolic curves for orthophosphate (Pi) and glucose-1-phosphate, and that they could not react with substrates with a blocked reducing end or alpha-1,6 glucosidic bonds. Antibodies prepared against the purified type-II form and cross-reacting with the type-I form showed that there was an increase in protein content during development and ripening of the fruit. The changes in protein level were parallel to those of phosphorylase activity, in both the phosphorolytic and synthetic directions. Considering the kinetics, indicating that starch phosphorylases are not under allosteric control, it can be argued that protein synthesis makes a contribution to regulating phosphorylase activity in banana fruit and that hormones, like gibberellic acid and indole-3-acetic acid, may play a regulating role. For the first time, starch phosphorylases isoforms were detected as starch-granule-associated proteins by immunostaining of SDS-PAGE gels.

Fruit↗
PubMed2002

Determination of the starch-phosphorylating enzyme activity in plant extracts.

For quantification of alpha-glucan, water dikinase (GWD) activity in crude extracts of plant tissues a radio-labeling assay was established that uses soluble starch and (33)P-labeled ATP as phosphate acceptor and donor, respectively. A constant rate of starch labeling was observed only if the ATP applied was labeled at the beta position. In wild-type extracts from leaves of Arabidopsis thaliana (L.) Heynh. the maximum rate of starch phosphorylation was approximately 27 pmol min(-1) (mg protein)(-1). Leaf extracts from the GWD-deficient sex1 mutants of Arabidopsis showed no significant incorporation of phosphate whereas extracts from potato (Solanum tuberosum L.) tuber expressing a GWD antisense construct exhibited less activity than the wild-type control. To our knowledge this is the first time that a quantification of the starch-phosphorylating activity has been achieved in plant crude extracts.

Adenosine Triphosphate↗
PubMed1998

A 56-kDa protein is a novel granule-bound starch synthase existing in the pericarps, aleurone layers, and embryos of immature seed in diploid wheat (Triticum monococcum L.).

A novel 56-kDa granule-bound starch synthase (GBSS; NDPglucose-starch glucosyltransferase, EC 2.4.1.21) responsible for amylose synthesis was found in the pericarps, aleurone layers and embryos of immature diploid wheat (Triticum monococcum L.). The GBSS and other proteins bound to starch granules of various tissues of immature normal and waxy diploid wheat seeds were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and their activities were examined. In the waxy mutant, the waxy protein (59.5 kDa, GBSSI) was absent, but amylose and GBSS activity were evident in all tissues except the endosperm. Of the proteins bound to starch granules, only the 56-kDa protein was associated with the presence of amylose and GBSS activities in the pericarps, aleurone layers and embryos. Mutations at the waxy locus did not affect the 56-kDa protein in these tissues. Changes in the amount of 56-kDa protein during the course of seed development, and the distribution of the 56-kDa protein in each tissue of immature seeds were quite different from those of the waxy protein. On the other hand, the N-terminal amino acid sequence of the 56-kDa protein had a 40-50% similarity to GBSSI of some other plant species and was antigenically related to the waxy protein. These results strongly suggest that the 56-kDa protein in diploid wheat is a GBSSI class enzyme and, hence, an isoform of the waxy protein. The waxy protein and 56-kDa protein, however, are expressed in different seed tissues and at different stages of seed development.

Amino Acid Sequence↗
PubMed2006

The effect of liquorice extract-containing starch gel on the amount and microbial composition of plaque.

The aim of this study was to find out whether liquorice-containing starch gel could affect plaque accumulation and its microbial composition. Sixteen healthy volunteers (mean age: 30.4+/-6.9 years) used 6 g of either control [8% acid-hydrolyzed corn starch, 25% maltitol syrup, water (w/w)] or liquorice gel (control + 2.5% liquorice extract), three times a day for 2 weeks. The gels were used in a random order with a 2-week washout period in between. At the end of each fortnight, plaque was allowed to accumulate for 2 days and all available plaque from the right side of the mouth was collected, weighed, and transferred to transport medium. The plaque on the left side was dyed and photographed in a standardized manner. Mutans streptococci, total streptococci, and facultative bacteria were assessed from the plaque using plate culturing. Plaque index (0-5) of incisors and canines on the left side was evaluated from the photographs. The clinical study was preceded by an in vivo acid production test. The acid production from gels containing 2.5-10% liquorice extract was monitored with a microelectrode. The in vivo acid production potential of the maltitol-containing starch gel was about 50% compared to the sucrose control. Liquorice inhibited acid production from the gel. In the clinical study, the weight of plaque after consumption of the liquorice gel did not differ from that of the control gel. No differences were found in the microbial counts nor in the plaque index between the two gels. In addition, the liquorice gel had no effect on the stability of the predominant bacterial populations of the plaque samples of 16 individuals as detected by PCR-denaturing gradient gel electrophoresis. In conclusion, an addition of liquorice extract to starch-containing gel with a low acid production potential had no effect on the plaque formed during a 2-week gel consumption period.

Acids↗
PubMed2004

Molecular characterization demonstrates that the Zea mays gene sugary2 codes for the starch synthase isoform SSIIa.

Mutations in the maize gene sugary2 ( su2 ) affect starch structure and its resultant physiochemical properties in useful ways, although the gene has not been characterized previously at the molecular level. This study tested the hypothesis that su2 codes for starch synthase IIa (SSIIa). Two independent mutations of the su2 locus, su2-2279 and su2-5178 , were identified in a Mutator -active maize population. The nucleotide sequence of the genomic locus that codes for SSIIa was compared between wild type plants and those homozygous for either novel mutation. Plants bearing su2-2279 invariably contained a Mutator transposon in exon 3 of the SSIIa gene, and su2-5178 mutants always contained a small retrotransposon-like insertion in exon 10. Six allelic su2 (-) mutations conditioned loss or reduction in abundance of the SSIIa protein detected by immunoblot. These data indicate that su2 codes for SSIIa and that deficiency in this isoform is ultimately responsible for the altered physiochemical properties of su2 (-) mutant starches. A specific starch synthase isoform among several identified in soluble endosperm extracts was absent in su2-2279 or su2-5178 mutants, indicating that SSIIa is active in the soluble phase during kernel development. The immediate structural effect of the su2 (-) mutations was shown to be increased abundance of short glucan chains in amylopectin and a proportional decrease in intermediate length chains, similar to the effects of SSII deficiency in other species.

Amylopectin↗
PubMed2003

Starch synthesis in the cereal endosperm.

The pathway of starch synthesis in the cereal endosperm is unique, and requires enzyme isoforms that are not present in other cereal tissues or non-cereal plants. Recent information on the functions of individual enzyme isoforms has provided insight into how the linear chains and branch linkages in cereal starch are synthesized and distributed. Genetic analyses have led to the formulation of models for the roles of de-branching enzymes in cereal starch production, and reveal pleiotropic effects that suggest that certain enzymes may be physically associated. For the first time, tools for global analyses of starch biosynthesis are available for cereal crops, and are heralded by the draft sequence of the rice genome.

1,4-alpha-Glucan Branching Enzyme↗