Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “STARCH”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21Linked to original sources
PubMed2005

Starch--value addition by modification.

Starch is one of the most important but flexible food ingredients possessing value added attributes for innumerable industrial applications. Its various chemically modified derivatives offer a great scope of high technological value in both food and non-food industries. Modified starches are designed to overcome one or more of the shortcomings, such as loss of viscosity and thickening power upon cooking and storage, particularly at low pH, retrogradation characteristics, syneresis, etc., of native starches. Oxidation, esterification, hydroxyalkylation, dextrinization, and cross-linking are some of the modifications commonly employed to prepare starch derivatives. In a way, starch modification provides desirable functional attributes as well as offering economic alternative to other hydrocolloid ingredients, such as gums and mucilages, which are unreliable in quality and availability. Resistant starch, a highly retrograded starch fractionformed upon food processing, is another useful starch derivative. It exhibits the beneficial physiological effects of therapeutic and nutritional values akin to dietary fiber. There awaits considerable opportunity for future developments, especially for tailor-made starch derivatives with multiple modifications and with the desired functional and nutritional properties, although the problem of obtaining legislative approval for the use of novel starch derivatives in processed food formulations is still under debate. Nevertheless, it can be predicted that new ventures in starch modifications and their diverse applications will continue to be of great interest in applied research.

Food Handling↗
PubMed2003

The role of two isoenzymes of alpha-amylase of Araucaria araucana (Araucariaceae) on the digestion of starch granules during germination.

Starch is the principal reserve of Araucaria araucana seeds, and it is hydrolysed during germination mainly by alpha-amylase. There are several alpha-amylase isoenzymes whose patterns change in the embryo and in the megagametophyte from the one observed in quiescent seeds (T(0)) to a different one observed 90 h after imbibition (T(90)). The objective of this research was to study the roles of two purified alpha-amylase isoenzymes by in vitro digestion of starch granules extracted from the tissues at two times of imbibition: one is abundant in quiescent seeds and the other is abundant after 90 h of imbibition. The isoenzymes digested the starch granules of their own stage of germination better, since the isoenzyme T(0) digested starch granules mainly from quiescent seeds, while the isoenzyme T(90) digested starch mainly at 90 h of imbibition. The sizes of the starch granule and the tissue from which these granules originated make a difference to digestion by the isoenzymes. Embryonic isoenzyme T(0) digested large embryonic starch granules better than small and medium-sized granules, and better than those isolated from megagametophytes. Similarly isoenzyme T(90) digested small embryonic starch granules better than medium-sized and large granules, and better than those isolated from megagametophytes. However, a mixture of partially purified megagametophytic isoenzymes T(0) and T(90) digested the megagametophytic granules better than those isolated from embryos. Studies of in vitro sequential digestion of starch granules with these isoenzymes corroborated their specificity. The isoenzyme T(90) digested starch granules previously digested by the isoenzyme T(0). This suggests that in vivo these two isoenzymes may act sequentially in starch granule digestion.

Carbohydrate Metabolism↗
PubMed1994

Bindability and digestibility of high-pressure-treated starch with glucoamylases from Rhizopus sp.

The effect of hydrostatic pressure on the bindability and digestibility of raw corn starch with two types of glucoamylase [EC 3.2.1.3] from Rhizopus sp., Gluc1 and Gluc2, was investigated in the range of 100 to 600 MPa. Pressurization of raw starch at 100 to 300 MPa for 1 h had no detectable effect, whereas pressurization at higher pressures than 400 MPa markedly enhanced the bindability and digestibility with Gluc1 and Gluc2, especially with Gluc2, which scarcely binds to raw starch and has much lower activity than Gluc1 towards raw starch. The binding constants Ks of Gluc1 and Gluc2 for the 400-MPa-pressurized starch reached 16 and 1.6 x 10(5) M-1, respectively, as compared with the Ks of 2.1 and 0.082 x 10(5) M-1 for raw starch. The 500- to 600-MPa-pressurized starch was digested by Gluc1 and Gluc2 at about 4.2 and 80 times higher rates, respectively, than raw starch. Thus, the high-pressure-treated starch was hardly distinguishable from high temperature (75 to 100 degrees C)-treated starch at least with respect to behavior with the enzymes, although some difference was observed between these starches by scanning electron microscopy and differential scanning calorimetry.

Calorimetry, Differential Scanning↗
PubMed2005

Sucrose synthase controls both intracellular ADP glucose levels and transitory starch biosynthesis in source leaves.

The prevailing model on transitory starch biosynthesis in source leaves assumes that the plastidial ADPglucose (ADPG) pyrophosphorylase (AGP) is the sole enzyme catalyzing the synthesis of the starch precursor molecule, ADPG. However, recent investigations have shown that ADPG linked to starch biosynthesis accumulates outside the chloroplast, presumably in the cytosol. This finding is consistent with the occurrence of an 'alternative' gluconeogenic pathway wherein sucrose synthase (SuSy) is involved in the production of ADPG in the cytosol, whereas both plastidial phosphoglucomutase (pPGM) and AGP play a prime role in the scavenging of starch breakdown products. To test this hypothesis, we have compared the ADPG content in both Arabidopsis and potato wild-type (WT) leaves with those of the starch-deficient mutants with reduced pPGM and AGP. These analyses provided evidence against the 'classical' model of starch biosynthesis, since ADPG levels in all the starch-deficient lines were normal compared with WT plants. Whether or not SuSy is involved in the synthesis of ADPG accumulating in leaves was tested by characterizing both SuSy-overexpressing and SuSy-antisensed transgenic leaves. Importantly, SuSy-overexpressing leaves exhibited a large increase of both ADPG and starch levels compared with WT leaves, whereas SuSy-antisensed leaves accumulated low amounts of both ADPG and starch. These findings show that (i) ADPG produced by SuSy is linked to starch biosynthesis; (ii) SuSy exerts a strong control on the starch biosynthetic process; and (iii) SuSy, but not AGP, controls the production of ADPG accumulating in source leaves.

Adenosine Diphosphate Glucose↗
PubMed2005

Starch-related alpha-glucan/water dikinase is involved in the cold-induced development of freezing tolerance in Arabidopsis.

Cold-induced soluble sugar accumulation enhances the degree of freezing tolerance in various cold-hardy plants including Arabidopsis (Arabidopsis thaliana), where soluble sugars accumulate in only a few hours at 2 degrees C. Hence, along with photosynthesis, starch degradation might play a significant role in cold-induced sugar accumulation and enhanced freezing tolerance. Starch-related alpha-glucan/water dikinase (EC 2.7.9.4), encoded by Arabidopsis STARCH EXCESS 1 (SEX1), is hypothesized to regulate starch degradation in plastids by phosphorylating starch, thereby ensuring better accessibility by starch-degrading enzymes. Here, we show that Arabidopsis sex1 mutants, when incubated at 2 degrees C for 1 d, were unable to accumulate maltooligosaccharides or normal glucose and fructose levels. In addition, they displayed impaired freezing tolerance. After 7 d at 2 degrees C, sex1 mutants did not show any of the above abnormal phenotypes but displayed slightly higher leaf starch contents. The impaired freezing tolerance of sex1 mutants was restored by overexpression of wild-type SEX1 cDNA using the cauliflower mosaic virus 35S promoter. The results demonstrate a genetic link between the SEX1 locus and plant freezing tolerance, and show that starch degradation is important for enhanced freezing tolerance during an early phase of cold acclimation. However, induction of starch degradation was not accompanied by significant changes in alpha-glucan/water dikinase activity in leaf extracts and preceded cold-induced augmentation of SEX1 transcripts. Therefore, we conclude that augmentation of SEX1 transcripts might be a homeostatic response to low temperature, and that starch degradation during an early phase of cold acclimation could be regulated by a component(s) of a starch degradation pathway(s) downstream of SEX1.

Adaptation, Physiological↗
PubMed2006

Carbon balance and circadian regulation of hydrolytic and phosphorolytic breakdown of transitory starch.

Transitory starch is formed in chloroplasts during the day and broken down at night. Transitory starch degradation could be regulated by light, circadian rhythms, or carbon balance. To test the role of these potential regulators, starch breakdown rates and metabolites were measured in bean (Phaseolus vulgaris) and Arabidopsis (Arabidopsis thaliana) plants. In continuous light, starch and maltose levels oscillated in a circadian manner. Under photorespiratory conditions, transitory starch breakdown occurred in the light faster than at night and glucose-6-P (G6P) was elevated. Nonaqueous fractionation showed that the increase in G6P occurred in the chloroplast. When Arabidopsis plants lacking the plastidic starch phosphorylase enzyme were placed under photorespiratory conditions, G6P levels remained constant, indicating that the increased chloroplastic G6P resulted from phosphorolytic starch degradation. Maltose was increased under photorespiratory conditions in both wild type and plants lacking starch phosphorylase, indicating that regulation of starch breakdown may occur at a point preceding the division of the hydrolytic and phosphorolytic pathways. When bean leaves were held in N2 to suppress photosynthesis and Suc synthesis without increasing photorespiration, starch breakdown did not occur and maltose and G6P levels remained constant. The redox status of the chloroplasts was found to be oxidized under conditions favoring starch degradation.

Arabidopsis↗
PubMed1994

Analysis of the raw starch-binding domain by mutation of a glucoamylase from Aspergillus awamori var. kawachi expressed in Saccharomyces cerevisiae.

Carboxy-terminal deletions were introduced into the raw starch-binding domain (A-515 to R-615) encoded by the gene for glucoamylase I (GAI) from Aspergillus awamori var. kawachi. Genes coding for proteins designated GA596 (A-1 to E-596), GA570 (A-1 to A-570), and GA559 (A-1 to N-559) were constructed and resulted in truncated proteins. All of the mutant genes were expressed heterologously in Saccharomyces cerevisiae. GA596 adsorbed to raw starch and digested it. GA570 and GA559 did not adsorb to raw starch or to an alpha-cyclodextrin-Sepharose CL-4B gel under our experimental conditions. However, GA570 was able to digest raw starch, and the digestion of raw starch by GA570 was inhibited by beta-cyclodextrin. Residue Trp-562 of GAI, which was suggested previously to contribute to formation of an inclusion complex with raw starch, was replaced by Leu (GAW562L), Phe (GAW562F), and Gly (GAW562G). GAW562L and GAW562F adsorbed to raw starch and an alpha-cyclodextrin gel, but GAW562G did not. Although GAW562L digested raw starch to the same extent as wild-type GAI (designated GAY), GAW562F and GAW562G exhibited less ability to digest raw starch. On the basis of our results, it appears that the sequence around Trp-562, PL(W-562)YVTVTLPA, is the minimal sequence necessary for digestion of raw starch and that hydrophobic residue Trp-562 contributes to formation of an inclusion complex. The sequence near Trp-589, which has abundant hydrogen bond-forming residues and the charged amino acid residues needed for stable adsorption to raw starch, probably assists in the formation of the inclusion complex.

Amino Acid Sequence↗
PubMed1999

Wheat bran affects the site of fermentation of resistant starch and luminal indexes related to colon cancer risk: a study in pigs.

BACKGROUND: Recent studies suggest that resistant starch (effective in producing butyrate and lowering possibly toxic ammonia) is rapidly fermented in the proximal colon; the distal colon especially would, however, benefit from these properties of resistant starch. AIMS: To determine whether wheat bran (a rich source of insoluble non-starch polysaccharides), known to hasten gastrointestinal transit, could carry resistant starch through to the distal colon and thus shift its site of fermentation. METHODS: Twenty four pigs were fed four human type diets: a control diet, or control diet supplemented with resistant starch, wheat bran, or both. Intestinal contents and faeces were collected after two weeks. RESULTS: Without wheat bran, resistant starch was rapidly fermented in the caecum and proximal colon. Supplementation with wheat bran inhibited the caecal fermentation of resistant starch, resulting in an almost twofold increase (from 12.9 (2.5) to 20.5 (2.1) g/day, p<0.05) in resistant starch being fermented between the proximal colon and faeces. This resulted in higher butyrate (133%, p<0.05) and lower ammonia (81%, p<0.05) concentrations in the distal colonic regions. CONCLUSIONS: Wheat bran can shift the fermentation of resistant starch further distally, thereby improving the luminal conditions in the distal colonic regions where tumours most commonly occur. Therefore, the combined consumption of resistant starch and insoluble non-starch polysaccharides may contribute to the dietary modulation of colon cancer risk.

Ammonia↗
PubMed2000

Comparative effects of three resistant starch preparations on transit time and short-chain fatty acid production in rats.

A high-fiber diet may protect against colon cancer because of the butyrate generated in the colon by bacterial fermentation of nonstarch polysaccharides. Butryrate can reverse neoplastic changes, at least in vitro, and resistant starch (RS) represents a source of butyrate in vivo. We examined the effects of replacing normal maize starch in the diet of rats with three preparations of RS on the amounts of starch, butyrate, and other short-chain fatty acids in the cecum. We examined the effects on fecal bulking and transit time, which have been suggested to protect against colon cancer. The RS preparations that we tested were potato starch, high-amylose maize starch, and an alpha-amylase-treated high-amylose maize starch. All had major effects on fecal weight and on the weight of the cecum but only slightly shortened transit times. All increased the amount of starch reaching the cecum and increased short-chain fatty acid production in the cecum; potato starch had the greatest effect and high-amylose maize starch the least. Potato starch, unlike high-amylose maize starch, enhanced the proportion of butyrate. Thus there were marked differences among sources of RS, even though these were all classified as RS2. The significance for colon cancer is discussed.

Animals↗
PubMed1999

The antimicrobial activity of vancomycin in the presence and absence of sodium carboxymethyl starch.

The purpose of this work was to determine any effects the presence of sodium carboxymethyl starch may have on the antimicrobial activity of vancomycin given a previously described interaction between vancomycin and sodium carboxymethyl starch. In particular, the in-vitro activity of vancomycin against two clinically relevant bacteria, Staphylococcus aureus and Enterococcus faecalis, was studied in the presence of varying concentrations of sodium carboxymethyl starch. From two independent studies conducted using an agar dilution method, it appeared that the binding of vancomycin to sodium carboxymethyl starch had no effect on the in-vitro antimicrobial activity of vancomycin. The minimum inhibitory concentration of vancomycin against S. aureus in the presence of as much as 1 mg mL(-1) sodium carboxymethyl starch was similar to that of the control where no sodium carboxymethyl starch was added (1-4 microg mL(-1) vs 1-2 microg mL(-1), respectively). Likewise, the minimum inhibitory concentration of vancomycin against E. faecalis in the presence of 1 mg mL(-1) sodium carboxymethyl starch was also similar to that of the control where no sodium carboxymethyl starch was added (1-4 microg mL(-1) vs 1-4 microg mL(-1), respectively). However, there may be factors in the in-vitro method, such as high ionic strength, that could disrupt the interaction between vancomycin and sodium carboxymethyl starch. Therefore, the possibility of diminished vancomycin activity in-vivo cannot be ruled out. A small percentage (8-10%) of vancomycin was determined to be bound to sodium carboxymethyl starch in broth media. Given these results, the impact of sodium carboxymethyl starch on the in-vitro antimicrobial activity of vancomycin is expected to be minimal. Binding studies could not be conducted with gelled agar due to its semi-solid state.

Anti-Bacterial Agents↗
PubMed1997

Starch utilization by ruminants: from basics to the bunk.

Starch is the major energy component of grains. Wheat contains 77% of DM as starch, corn and sorghum contain 72%, and barley and oats contain 57 to 58%. In vitro systems have provided valuable data on kinetic aspects of starch digestion. Molecular biological techniques have provided a clearer picture of the ruminal microbial milieu. Proportions of starch fermented in the rumen can be predicted satisfactorily for a variety of grains and processing methods. Compared with dry rolling, steam processing (flaking or rolling) increases ruminal digestibility of starch (percentage of intake) from 52 to 78% for sorghum, from 75 to 85% for corn, and six percentage units or less for other grains. Recent research provides new insight into pancreatic function and intestinal glucose transport systems. The capacity to digest starch in the intestine ranges from 45 to 85% of starch entering the duodenum, with that capacity apparently limited by the supply of pancreatic amylase. There is evidence that amylase secretion may be enhanced by increasing duodenal entry of protein. Capacity for active transport of glucose across of gut wall does not seem to limit the amount of starch digested that is absorbed as glucose. For ruminants eating medium- to high-concentrate diets, about 30% of their total glucose need comes from glucose absorption, 50% from organic acid absorption (substrates for hepatic gluconeogenesis), and 20% from other sources. When glucose absorption from the gut increases, ruminants generally adjust (decrease) gluconeogenesis to meet their need; that need is directly linked to DE intake. In terms of overall ME yield, grain starch is best used when it is fermented in the rumen. However, close coordination of protein and starch supply to the duodenum may improve capture of starch in the form of glucose.

Animals↗
PubMed1985

Effect of sorghum grain variety and reconstitution on site and extent of starch and protein digestion in steers.

Hetero-yellow (HY), red (RED) and brown (BR, high tannin) sorghums were fed dry-rolled or reconstituted (RED and BR only) to evaluate the effect of variety and reconstitution on the site and extent of starch and protein digestion in steers fitted with ruminal, duodenal and ileal cannulae. Processed grains were incorporated into 88% sorghum (DM basis) diets fed at 2% of body weight in a 5 X 5 Latin square. Ruminal fermentation of organic matter, starch and protein tended to be lower for the dry-rolled RED than for either the dry-rolled HY or BR sorghum. Digestion of organic matter (OM) and starch in the small intestine was very low for dry-rolled sorghums. Total tract starch digestibility was lower for the dry-rolled RED sorghum (86.9%) than the BR (90.8%) and HY (91.4%). Nitrogen (N) digestibility ranged from 53.1% for the dry-rolled BR to 64.5% for the HY. Tannins were extensively (95.2%) degraded in the rumen, which may have enhanced fermentation of the BR sorghum. Reconstitution increased (P less than .05) total-tract starch digestion of the RED and tended to increase starch digestion of the BR as well. Total N flow to the duodenum tended to increase with reconstitution, with most of the increase being due to greater (P less than .05) microbial-N. Reconstitution also increased (P less than .05) total-tract N digestibility of the RED. The response to reconstitution for the RED sorghum appeared to be due primarily to an increase (P less than .10) in the extent of fermentation of organic matter and starch in the rumen. Reconstitution of BR, however, enhanced disappearance of starch from the small intestine. In both cases, most (97.3%) of the digestible starch of the reconstituted sorghums had disappeared before the terminal ileum. In contrast, 14.5% (621 g) of the digestible starch of dry-rolled RED disappeared in the large intestine. Sorghum grain variety and reconstitution appear to alter site and extent of starch and protein digestion, which may result in variable performance of cattle fed sorghum grain diets.

Animal Feed↗
PubMed2000

Acetylation and characterization of banana (Musa paradisiaca) starch.

Banana native starch was acetylated and some of its functional properties were evaluated and compared to corn starch. In general, acetylated banana starch presented higher values in ash, protein and fat than corn acetylated starch. The modified starches had minor tendency to retrogradation assessed as % transmittance of starch pastes. At high temperature acetylated starches presented a water retention capacity similar to their native counterpart. The acetylation considerably increased the solubility of starches, and a similar behavior was found for swelling power. When freeze-thaw stability was studied, acetyl banana starch drained approximately 60% of water in the first and second cycles, but in the third and fourth cycles the percentage of separated water was low. However, acetyl corn starch showed lower freeze-thaw stability than the untreated sample. The modification increased the viscosity of banana starch pastes.

Freezing↗
PubMed2003

[Physicochemical and functional evaluation of pregelatinized and microwaved cassava (Manihot esculenta Cranz) starches].

The aim of this study was to evaluate the effect of two physical modification methods, drum-drying pregelatinization and microwave heating (at 25% moisture), on some characteristics of cassava starch. The water absorption, solubility and swelling power of pregelatinized starch increased considerably between 65 and 90 degrees C (56 to 86 g water/g starch, 89 to 99% and 63 to 87, respectively), while in microwaved starch these indices dropped, in general terms, from 75 degrees C (5 to 37 g water/g starch, 1 to 37% and 12 to 38 respectively) compared to native starch values (10 to 40 g water/g starch, 2 to 40% and 13 to 41, respectively). All samples showed a marked breakdown during heating, while the pregelatinized starch has the lowest setback values. The morphology of microwaved starch was slightly affected, while in the pregelatinized starch all vestige of granular integrity disappeared. Of the two methods used, pregelatinization caused the most remarkable changes of cassava starch characteristics.

Chemical Phenomena↗
PubMed1989

Proliferative activity in the colon of the mouse and its modulation by dietary starch, fat, and cellulose.

The effect of dietary starch, fat, and cellulose on colonic proliferation was studied in female C57Bl/6J mice after 4 weeks of feeding with diets containing various levels of starch (3, 36, and 57-65%), various levels of fat (corn oil, 5 and 29%) and various levels of cellulose (2 and 10%). Cell proliferation was measured by colchicine arrest and [3H]thymidine incorporation. The following parameters were analyzed: mitotic index, labeling index, and position of labelled cells along the crypt. Increasing starch content from 3 to 36% decreased cell proliferation both in low (5%) and high (29%) fat diets. By estimating simultaneously the effects of starch and fat with a single multiple regression model, we observed a decrease of mitotic index from 3.04 +/- 0.34 to 2.04 +/- 0.43 (means +/- SE) (P less than 0.05) when starch was increased from 3 to 36% regardless of the level of fat. Other proliferation parameters showed a similar pattern. Changes in dietary fat alone did not affect significantly cell proliferation. We also investigated the effect of starch at high levels (57-65%) and its interactions with cellulose. High starch (57-65%) increased the labeling index from 7.70 +/- 0.58 to 9.65 +/- 0.88 (P less than 0.05), when also considering the effect of cellulose in the multiple regression model. Cellulose by itself did not change the labeling index. Varying starch from 36 to 57-65% increased the number of cells/crypt column from 22.20 +/- 0.82 to 25.87 +/- 1.21 (P less than 0.05) and varying cellulose from 2 to 10% increased the number of cells/crypt column from 22.20 +/- 0.82 to 27.25 +/- 0.97 (P less than 0.01). The results indicate that either high or low fat diets, containing 36% starch, have the minimum proliferative effects in the mouse colon. However, diets containing high levels of both starch (57%) and cellulose (10%) may induce an increase in proliferation. These data suggest a potential beneficial effect of starch on colon proliferation.

Animals↗
PubMed1998

Seasonal fluctuations of starch in root and stem tissues of coppiced Salix viminalis plants grown under two nitrogen regimes.

Seasonal changes in starch were studied at the tissue and cellular levels in roots and stems of Salix viminalis L. cuttings. Cuttings were planted in pots containing sand and grown in a controlled environment chamber in which seasons were artificially induced by changes in temperature and photoperiod. Nitrogen was supplied at optimum and low rates, and during dormancy, one-half of the plants were decapitated. Starch concentrations in root and stem tissues were determined regularly during shoot extension growth, dormancy and resprouting after dormancy. We used light microscopy (LM) combined with image analysis (IA) to determine the cellular localization and amount of starch in different cell types of stem and root tissues. Chemical analysis confirmed that starch concentrations were lower in plants receiving a high-N supply rate than in plants receiving a low-N supply rate. In all plants, the highest concentration of starch was in the roots. Light microscopy and IA showed that starch accumulated mainly in the phloem and cortical cells of both root and stem tissues. Starch grains were also regularly found in ray parenchyma cells. The amount of starch as well as the size of the grains showed strong seasonal fluctuations. In both roots and stems, starch concentrations were highest during predormancy and lowest during periods of shoot extension growth. At the time of resprouting, root cells of decapitated plants were more depleted of starch than root cells of intact plants, supporting the hypothesis that starch reserves in roots are important during the early phase of resprouting in coppice systems.

Journal Article↗
PubMed1971

Starch metabolism in the leaf sheaths and culm of rice.

The levels of starch and dextrin, free sugars, soluble protein, and enzymes involved in starch metabolism-alpha-amylase, beta-amylase, phosphorylase, Q-enzyme, R-enzyme, and ADP-glucose starch synthetases-were assayed in the leaf sheaths and culm of the rice plant (Oryza sativa L., variety IR8) during growth.Starch accumulation in the leaf sheaths reached a maximum 10 to 11 weeks after transplanting, the time of development of the rice panicle. Maximal concentration of free sugars occurred earlier. Starch and sugars in the leaf sheaths and culm decreased rapidly during grain development.During starch accumulation, the starch granules of the leaf sheaths increased slightly in size and its gelatinization temperature decreased. The molecular size of amylose and amylopectin and amylose content of the starch were similar in both culm and leaf sheaths.Changes in the level of soluble protein paralleled changes in starch level in the leaf sheaths. Among the enzymes, only synthetase bound to the starch granule paralleled the level of starch in the leaf sheaths and in the culm. ADP-glucose, but not UDP-glucose, was utilized as a glucosyl donor by these starch synthetases. Zymograms of these extracts showed only one alpha-amylase band, one beta-amylase band, two phosphorylase bands, and one Q-enzyme band.

Journal Article↗
PubMed1982

Biochemical Basis for Partitioning of Photosynthetically Fixed Carbon between Starch and Sucrose in Soybean (Glycine max Merr.) Leaves.

The control of photosynthetic starch/sucrose formation in leaves of soybean (Glycine max L. Merr.) cultivars was studied in relation to stage of plant development, photosynthetic photoperiod, and nitrogen source. At each sampling, leaf tissue was analyzed for starch content, activities of sucrose-metabolizing enzymes, and labeling of starch and sucrose (by (14)CO(2) assimilation) in isolated cells. In three of the four varieties tested, nodulated plants had lower leaf starch levels and higher activities of sucrose phosphate synthetase (SPS), and isolated mesophyll cells incorporated more carbon (percentage of total (14)CO(2) fixed) into sucrose and less into starch as compared to nonnodulated (nitrate-dependent) plants. The variation among cultivars and nitrogen treatments observed in the activity of SPS in leaf extracts was positively correlated with labeling of sucrose in isolated cells (r = 0.81) and negatively correlated with whole leaf starch content (r = -0.66). The results suggested that increased demand for assimilates by nodulated roots may be accommodated by greater partitioning of carbon into sucrose in the mesophyll cells. We have also confirmed the earlier report (Chatterton, Silvius 1979 Plant Physiol 64: 749-753) that photoperiod affects partitioning of fixed carbon into starch. Within two days of transfer of nodulated soybean Ransom plants from a 14-hour to a 7-hour photoperiod, leaf starch accumulation rates doubled, and this effect was associated with increased labeling of starch and decreased labeling of sucrose in isolated cells. Concurrently, activities of SPS, sucrose synthase, and uridine diphosphatase in leaves were decreased.Four nodulated soybean cultivars were grown to maturity in a greenhouse. Fully expanded leaves at the top of the canopy were sampled during vegetative growth (45 days), at flowering (79 days), and at mid-podfill (120 days). In general, activities of SPS and uridine-5'-diphosphatase were highest during vegetative growth, and they decreased during reproductive development, whereas activity of sucrose synthase and leaf starch content tended to increase. Leaf starch was negatively correlated with levels of SPS (r = -0.71). The results support the postulate that sucrose-P synthetase is a key control point regulating the photosynthetic formation of sucrose, and, hence, starch.

Journal Article↗