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At least 739 records · Page 41Linked to original sources
PubMed1988

Effect of temperature on starch synthesis in potato tuber tissue and in amyloplasts.

A sharp temperature optimum is observed at 21.5 degrees C when the incorporation of [(14)C]sucrose into starch is measured with discs cut from developing tubers of potato (Solanum tuberosum L. cv Desirée). By contrast, increasing temperatures over the range 9 to 31 degrees C only enhance release of (14)C to respiratory CO(2) and incorporation of (14)C into the ethanolsoluble fraction. By comparison, starch synthesis in discs from developing corms of cocoyam (Colocasia esculenta L. Schott) is increased by raising the temperature from 15 to 35 degrees C. The significance of a relatively low temperature optimum for starch synthesis in potato is discussed in relation to the yield limitations imposed by continuously high soil temperatures. Amyloplasts isolated from protoplasts prepared from developing potato tubers contain activities of alkaline pyrophosphatase, NAD-dependent glyceraldehyde-3-phosphate dehydrogenase, fructose-1,6-bisphosphatase, and phosphoglucomutase in addition to ADP-glucose-pyrophosphorylase, starch phosphorylase and starch synthase. Cell-free amyloplasts released by thinly slicing developing potato tubers synthesize starch from [(14)C]triose-phosphate generated from [(14)C]fructose-1,6-bisphosphate in the reaction medium. This starch synthesis is inhibited by addition of 10 millimolar inorganic phosphate and requires amyloplast integrity, suggesting the operation of a triose-phosphate/inorganic phosphate exchange carrier at the amyloplast membrane. The temperature optimum at 21.5 degrees C observed with tissue discs is not observed with amyloplasts.

Journal Article↗
PubMed1989

Acclimation of Two Tomato Species to High Atmospheric CO(2): I. Sugar and Starch Concentrations.

Lycopersicon esculentum Mill. cv Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO(2) concentrations (330 or 900 microliters per liter) for 10 weeks. Tomato plants grown at 900 microliters per liter contained more starch and more sugars than the control. However, we found no significant accumulation of starch and sugars in the young leaves of L. esculentum exposed to high CO(2). Carbon exchange rates were significantly higher in CO(2)-enriched plants for the first few weeks of treatment but thereafter decreased as tomato plants acclimated to high atmospheric CO(2). This indicates that the long-term decline of photosynthetic efficiency of leaf 5 cannot be attributed to an accumulation of sugar and/or starch. The average concentration of starch in leaves 5 and 9 was always higher in L. esculentum than in L. chmielewskii (151.7% higher). A higher proportion of photosynthates was directed into starch for L. esculentum than for L. chmielewskii. However, these characteristics did not improve the long-term photosynthetic efficiency of L. chmielewskii grown at high CO(2) when compared with L. esculentum. The chloroplasts of tomato plants exposed to the higher CO(2) concentration exhibited a marked accumulation of starch. The results reported here suggest that starch and/or sugar accumulation under high CO(2) cannot entirely explain the loss of photosynthetic efficiency of high CO(2)-grown plants.

Journal Article↗
PubMed1990

Regulation of photosynthate partitioning into starch in soybean leaves : response to natural daylight.

Studies conducted in controlled environments indicate that daylength affects the proportion of photosynthate stored in leaves as starch or sucrose. To examine the response of partitioning to natural daylight, soybeans (Glycine max [L.] Merr. cv Williams) were grown at 12 different times between May and November in a constant temperature greenhouse without supplemental lighting. Plants were transferred from the greenhouse to a controlled environment chamber at the end of civil twilight at a set developmental stage (expanding seventh trifoliolate leaf, counting acropetally). Net photosynthesis and the accumulation of starch and sugar in fully expanded fourth trifoliolate leaves were determined the following day under standard conditions in the chamber (lights-on synchronized with sunrise). Photosynthesis on a leaf area basis decreased about 10% between midsummer and early autumn. Leaf soluble sugar accumulation was low at all harvests. However, a twofold increase in photosynthate partitioning into starch occurred over the same time period, resulting in an 80% increase in absolute starch accumulation rate. Starch was responsible for about 78% of the increase in leaf dry matter during the light at all harvests, indicating that starch accumulation as affected by prior daylight conditions will alter export of photosynthate during the light period. Photosynthate partitioning into starch was linearly correlated with daylength at harvest, prior average peak solar irradiance, and other parameters that correlated with daylength and solar radiation such as harvested top dry matter. The relation between growth and seasonal changes in daylight (including daylength, irradiance, and light integral) are discussed in relation to photosynthate partitioning under field conditions.

Journal Article↗
PubMed1990

Sugar uptake and starch biosynthesis by slices of developing maize endosperm.

(14)C-Sugar uptake and incorporation into starch by slices of developing maize (Zea mays L.) endosperm were examined and compared with sugar uptake by maize endosperm-derived suspension cultures. Rates of sucrose, fructose, and d- and l-glucose uptake by slices were similar, whereas uptake rates for these sugars differed greatly in suspension cultures. Concentration dependence of sucrose, fructose, and d-glucose uptake was biphasic (consisting of linear plus saturable components) with suspension cultures but linear with slices. These and other differences suggest that endosperm slices are freely permeable to sugars. After diffusion into the slices, sugars were metabolized and incorporated into starch. Starch synthesis, but not sugar accumulation, was greatly reduced by 2.5 millimolar p-chloromercuribenzenesulfonic acid and 0.1 millimolar carbonyl cyanide m-chlorophenylhydrazone. Starch synthesis was dependent on kernel age and incubation temperature, but not on external pH (5 through 8). Competing sugars generally did not affect the distribution of (14)C among the soluble sugars extracted from endosperm slices incubated in (14)C-sugars. Competing hexoses reduced the incorporation of (14)C into starch, but competing sucrose did not, suggesting that sucrose is not a necessary intermediate in starch biosynthesis. The bidirectional permeability of endosperm slices to sugars makes the characterization of sugar transport into endosperm slices impossible, however the model system is useful for experiments dealing with starch biosynthesis which occurs in the metabolically active tissue.

Journal Article↗
PubMed1991

A Quantification of the Significance of Assimilatory Starch for Growth of Arabidopsis thaliana L. Heynh.

These studies use starch synthesis mutants to quantify the contribution of assimilatory starch to whole plant growth and form. Arabidopsis thaliana (L.) Heynh plants were used with null plastid phosphoglucomutase (T Caspar, SC Huber, CR Sommerville, [1986] Plant Physiol 79; 1-7) or 7% of wild-type ADP-glucose pyrophosphorylase (T-P Lin, T Caspar, CR Sommerville, J Preiss [1988] Plant Physiol 88; 1175-1179). The daily turnover of starch and the rate of biomass increase in the mutants and the wild type were investigated during growth in a 14 hour light/10 hour dark cycle in high irradiance (600 micromoles per square meter per second) and nitrogen (6 millimolar NH(4)NO(3)), in high irradiance and low nitrogen (0.1 millimolar NH(4)NO(3)) or in low irradiance (80 micromoles per square meter per second) and high nitrogen. There is some variability in the data, but the following conclusions can be drawn. Growth was slow in the absence of starch turnover. In high nitrogen conditions, about 1 mole of carbon per gram dry weight per day was incorporated additionally into structural biomass for every one mole of carbon turned over as starch per gram dry weight per day. In low nitrogen, the gain was much lower. This indicates that temporary storage of photosynthate is important for rapid growth in high nitrogen, but not in low nitrogen when carbohydrate is in excess. Starch-deficient plants showed the usual decrease of the shoot/root ratio in low nitrogen and increase of the ratio in low light. This shows that adjustment of plant form to nitrogen nutrition and irradiance is not mediated via regulation of photosynthate partitioning in the leaf. Starch deficient plants had lower shoot/root ratios than the wild type and the nitrogen concentration in their leaves was increased. It is discussed how interactions between carbohydrate allocation, respiration and growth at the organ and whole plant level generate these changes. We conclude that mutants with a decreased capacity to carry out a particular partial process provide a powerful tool to disect complex mutually interacting systems, and define and quantify causal interactions at the level of whole plant growth.

Journal Article↗
PubMed1991

Influence of water deficit on maize endosperm development : enzyme activities and RNA transcripts of starch and zein synthesis, abscisic Acid, and cell division.

In maize (Zea mays L.), drought during the post-pollination stage decreases kernel growth and often leads to grain yield losses. Kernels in the apical region of the ear are more severely affected than basally positioned kernels. We hypothesized that water deficit during early endosperm development might inhibit kernel growth by decreasing endosperm cell division, and that this response might be mediated by changes in endosperm abscisic acid (ABA) levels. Greenhouse-grown maize, cultivar Pioneer 3925, was subjected to water limitation from 1 to 15 days after pollination (DAP), spanning the period of endosperm cell division and induction of storage product accumulation. Water deficit decreased the number of endosperm nuclei during the treatment period; the most substantial effect was in the apical region of ears. Correspondingly, endosperm fresh weight, starch accumulation and dry mass at maturity were decreased by water limitation. Abscisic acid concentrations in endosperm were quantified by enzyme-linked immunosorbent assay. Water deficit increased ABA concentration in apical-region endosperm by four-fold compared to controls. ABA concentrations were also increased in middle and basal regions of the ear, but to a lesser extent. Two key enzymes in the starch synthesis pathway, sucrose synthase and granule-bound ADP-glucose starch synthase, and zein, the major storage protein in maize endosperm, were studied as markers of storage product synthesis. Water deficit did not affect sucrose synthase enzyme activity or RNA transcript abundance relative to total RNA. However, ADP-glucose starch synthase activity and RNA transcript abundance decreased slightly in apical-region endosperm of water-limited plants by 15 DAP, compared with well-watered controls. In contrast to starch, there was no treatment effect on the accumulation of zein, evaluated at either the polypeptide or RNA level. We conclude that under the conditions tested, the establishment of starch and zein synthetic potential in endosperm was only slightly affected by plant water deficit during the early phase of kernel growth, and that capacity for growth and starch accumulation was affected by the extent to which cell division was inhibited. Based on correlative changes in ABA concentration and cell division we suggest that ABA may play a role in inhibiting endosperm cell division during water limitation.

Journal Article↗
PubMed1992

Regulation of photosynthesis by end-product accumulation in leaves of plants storing starch, sucrose, and hexose sugars.

In the present study, leaves of different plant species were girdled by the hot wax collar method to prevent export of assimilates. Photosynthetic activity of girdled and control leaves was evaluated 3 to 7 days later by two methods: (a) carbon exchange rate (CER) of attached leaves was determined under ambient CO(2) concentrations using a closed gas system, and (b) maximum photosynthetic capacity (A(max)) was determined under 3% CO(2) with a leaf disc O(2) electrode. Starch, hexoses, and sucrose were determined enzymically. Typical starch storers like soybean (Glycine max L.) (up to 87.5 milligrams of starch per square decimeter in girdled leaves), cotton (Gossypium hirsutum L.), and cucumber (Cucumis sativus L.) responded to 7 days of girdling by increased (80-100%) stomatal resistance (r(s)) and decreased A(max) (>50%). On the other hand, spinach (Spinacia oleracea L.), a typical sucrose storer (up to 160 milligrams of sucrose per square decimeter in girdled leaves), showed only a slight reduction in CER and almost no change in A(max). Intermediate plants like tomato (Lycopersicon esculentum Mill.), sunflower (Helianthus annuus L.), broad bean (Vicia faba L.), bean (Phaseolus vulgaris L.), and pea (Pisum sativum L.), which upon girdling store both starch and sucrose, responded to the girdle by a considerable reduction in CER but only moderate inhibition of A(max), indicating that the observed reduction in CER was primarily a stomatal response. Both the wild-type tobacco (Nicotiana sylvestris) (which upon girdling stored starch and hexoses) and the starchless mutant (which stored only hexoses, up to 90 milligrams per square decimeter) showed 90 to 100% inhibition of CER and approximately 50% inhibition of A(max). In general, excised leaves (6 days) behaved like girdled leaves of the respective species, showing 50% reduction of A(max) in wild-type and starchless N. sylvestris but only slight decline of A(max) in spinach. The results of the present study demonstrate the possibility of the occurrence of end-product inhibition of photosynthesis in a large number of crop plants. The long-term inhibition of photosynthesis in girdled leaves is not confined to stomatal responses since the A(max) declined up to 50%. The inhibition of A(max) by girdling was strongest in starch storers, but starch itself cannot be directly responsible, because the starchless mutant of N. sylvestris was also strongly inhibited. Similarly, the inhibition cannot be attributed to hexose sugars either, because soybean, cotton, and cucumber are among the plants most strongly inhibited although they do not maintain a large hexose pool. Spinach, a sucrose storer, showed the least inhibition in both girdled and excised leaf systems, which indicates that sucrose is probably not directly responsible for the end-product inhibition of photosynthesis. The occurrence of strong end-product inhibition appears to be correlated with high acid-invertase activity in fully expanded leaves. The inhibition may be related to the nature of soluble sugar metabolism in the extrachloroplastic compartment and may be caused by a metabolite that has different rates of accumulation and turnover in sucrose storers and other plants.

Journal Article↗
PubMed2004

Field performance and starch characteristics of high-amylose potatoes obtained by antisense gene targeting of two branching enzymes.

Potato is an important crop for starch production, but there are limitations regarding the genetic variation of starch quality. In maize, starches with various properties have been available for a long time by mutational breeding. Amylose starch from potatoes differs from cereal amyloses in several functionally important aspects, such as a higher degree of polymerization. Areas of application in which the degree of polymerization is of importance include film forming and the polymeric properties of bioplastics. High-amylose potato lines have been achieved by inhibiting the two known branching enzyme forms of potato. A single inserted gene construct for the inhibition of both forms resulted in structural changes of the starch to levels of branching that were below the commercially available amylose standards of potato. The high-amylose potato lines were tested in multiple year field trials of agronomic performance and were used for the pilot plant production of starch. The introduced trait was confirmed to be stable over multiple years. The consequences of the modification were found to be an increased tuber yield, reduced starch content, smaller granule size and an increase in reducing sugars.

Journal Article↗
PubMed1988

Production and Characteristics of Raw-Potato-Starch-Digesting alpha-Amylase from Bacillus subtilis 65.

A newly isolated bacterium, identified as Bacillus subtilis 65, was found to produce raw-starch-digesting alpha-amylase. The electrophoretically homogeneous preparation of enzyme (molecular weight, 68,000) digested and solubilized raw corn starch to glucose and maltose with small amounts of maltooligosaccharides ranging from maltotriose to maltoheptaose. This enzyme was different from other amylases and could digest raw potato starch almost as fast as it could corn starch, but it showed no adsorbability onto any kind of raw starch at any pH. The mixed preparation with Endomycopsis glucoamylase synergistically digested raw potato starch to glucose at 30 degrees C. The raw-potato-starch-digesting alpha-amylase showed strong digestibility to small substrates, which hydrolyzed maltotriose to maltose and glucose, and hydrolyzed p-nitrophenyl maltoside to p-nitrophenol and maltose, which is different from the capability of bacterial liquefying alpha-amylase.

Journal Article↗
PubMed1990

Nutrients excreted in ileostomy effluents after consumption of mixed diets with beans or potatoes. II. Starch, dietary fibre and sugars.

The extent of carbohydrate digestion and absorption from two diets including either instant bean flakes (174 g/d) or potato flakes (102 g/d) was measured in seven ileostomy subjects during a 2-day period. Test foods contributed 40 per cent of the total dietary starch intake (160 g/d), the remainder coming from rice and white bread. Overall, 4 per cent and 0.7 per cent of the dietary starch consumed remained unabsorbed during the bean and potato periods, respectively. Between 9.0 and 10.9 per cent of dietary bean starch and less than 1.7 per cent of potato starch were not absorbed. Dietary fibre and resistant starch were completely recovered in ileostomy effluents. In separate meal tests with 40 g starch, beans gave lower blood glucose (P less than 0.05) and serum insulin (P less than 0.01) responses than potatoes. Dietary starch malabsorption from leguminous foods is less than previously estimated and does not explain the attenuated glycaemic and insulinaemic responses.

Adult↗
PubMed1978

[Second increase in plasma volume after single infusion of hydroxyethyl starch (author's transl)].

6 patients without evidence for renal, hepatic or pancreatic disease were treated with intravenous infusions of 500 ml hydroxyethyl starch (6%) over a period of 60 min. In the course of the infusion we observed an increase in plasma volume from 2.72 +/- 0.101 to 3.36 +/- 0.141. After 2 h plasma volume decreased to 3.02 +/- 0.101 but showed a second peak of 3.23 +/- 0.121 after 4 h (p less than 0.01). 24 h following infusion an increase in plasma volume of 4,8% was found as compared to preinfusion values. The second increase in plasma volume cannot be explained by the total concentration of hydroxyethyl starch since the latter decreased continuously. The increase in plasma volume was accompanied by a decrease in average molecular weight (-Mw and -Mn). It is suggested that serum amylase produces small osmotic active molecules by degradation of hydroxyethyl starch, thus leading to an increase in plasma volume. 12--24 h after the infusion of hydroxyethyl starch serum amylase was more than twice as high basal values. This is caused by the formation of a high molecular hydroxyethyl starch-amylase-complex which cannot be eliminated easily. When hydroxyethyl starch is given repeatedly to normovolemic patients, the second increase in plasma volume should be considered as a possible cause for acute hypervolemia. This is especially true for patients with myocardial insufficiency.

Adult↗
PubMed2004

Identification and characterization of a novel cassava (Manihot esculenta Crantz) clone with high free sugar content and novel starch.

This study reports the identification of a new class of cassava (Manihot esculenta Crantz) with a storage root showing unusual free sugar accumulation and novel starch. Twenty-seven clones high in free sugar were identified under cultivation in primitive rural community areas in the Amazon. Iodine test and glucose oxidase-peroxidase reagent strips were used, in the field, for identification of starch and glucose, respectively. Five out of these 27 clones of cassava were cultivated at EMBRAPA Genetic Resources and Biotechnology and used for biochemical characterization, starch synthesis enzyme activities and gene expression analysis. Carbohydrates were fractioned into free sugar, polymerized water-soluble and -insoluble alpha-polyglucan. Clones of series CAS36 accumulate over 100 times more free sugar (mainly glucose) than commercial varieties. Monosaccharide composition analysis revealed one clone with distinct water-soluble sugars not present in the commercial cultivar. Structure analysis of the water-soluble and -insoluble alpha-polyglucan revealed the presence of a glycogen-like starch in clone CAS36.1. This clone indicated disruption in the starch synthesis pathway for enzyme activities and protein blot analyses in ADPG-pyrophosphorylase and branching enzyme, and their corresponding protein. Gene expression analysis indicated the lack of transcript for the gene coding for branching enzyme, but not for the gene coding for the ADPG-pyrophosphorylase small subunit. In addition, the pattern of distribution of sugar and starch content showed to be related to tissue age in the storage root.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1994

Soybean cotyledon starch metabolism is sensitive to altered gravity conditions.

We have demonstrated that etiolated soybean seedlings grown under the altered gravity conditions of clinorotation (1 rpm) and centrifugation (5xg) exhibit changes in starch metabolism. Cotyledon starch concentration was lower (-28%) in clinorotated plants and higher (+24%) in centrifuged plants than in vertical control plants. The activity of ADP-glucose pyrophosphorylase in the cotyledons was affected in a similar way, i.e. lower (-37%) in the clinorotated plants and higher (+22%) in the centrifuged plants. Other starch metabolic enzyme activities, starch synthase, starch phosphorylase and total hydrolase were not affected by the altered gravity treatments. We conclude that the observed changes in starch concentrations were primarily due to gravity-mediated differences in ADP-glucose pyrophosphorylase activity.

Centrifugation↗
PubMed2026

A Meta-learning-driven strategy for adulteration detection in sweet potato starch and vermicelli using Raman spectroscopy.

To address the widespread adulteration of sweet potato starch and its vermicelli with cheaper starches and overcome conventional supervised learning's dependency on large labeled datasets, this study developed a few-shot discrimination method integrating Raman spectroscopy with meta-learning. We constructed a meta-learning framework using cassava- and wheat-adulterated sweet potato starch as the source domain for training, with potato-adulterated sweet potato starch and cassava-adulterated sweet potato vermicelli as two target domains for testing. Raman spectra showed high consistency between sweet potato vermicelli and its raw starch, laying the foundation for cross-domain detection. Testing yielded comprehensive classification accuracies of 95.33% and 98.00% for the two target domains, significantly outperforming SVM, RF, and CNN (max. 85.24%). This approach effectively identifies subtle starch variety differences in complex adulteration, providing novel food quality inspection solutions and verifying the feasibility of raw material-to-finished product cross-domain detection.

Ipomoea batatas↗
PubMed2026

Insights into specific and nonspecific butyrate-producing pathways during the in vitro fecal fermentation of butyrylated starch.

Butyrylated starch is a special type-4 resistant starch with butyrate-carrying attribute. In this study, the unique butyrate-producing capability of butyrylated starch was deeply investigated by focusing on its specific and nonspecific butyrate-producing pathways, respectively, using specially designed substrates as controls. In vitro fermentation studies revealed that butyrylated and isobutyrylated starches generated high levels of butyrate and isobutyrate, respectively, highlighting the role of butyryl group metabolism in the specificity of butyrate production. Carboxylesterase assays have demonstrated that butyryl group metabolism is primarily facilitated by carbohydrate esterases expressed in the gut microbiota. Combined with 16S rRNA sequencing and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, it was found that butyrylated starch fermentation did not significantly enhance traditional butyrate synthesis pathways but modified the balance between the butyryl-CoA:acetyl-CoA transferase and butyrate kinase pathways by altering the gut microbiota composition, specifically by upregulating the relative abundance of indicator species such as Bacteroides, the Lachnospiraceae_NK4A136_group, and Parabacteroides. These insights offer theoretical guidance for designing butyrylated starch structures and regulating intestinal health.

Starch↗
PubMed1996

Cloning and functional analysis of a cDNA encoding a novel 139 kDa starch synthase from potato (Solanum tuberosum L.).

Three isoforms of starch synthase were shown to be present in soluble potato tuber extracts by activity staining after native gel electrophoresis. An antibody directed against a domain conserved in starch synthases was used to clone a cDNA for one of these isoforms by screening a tuber-specific expression library. A partial cDNA of 2.6 kbp was obtained and used to isolate a full-length cDNA of 4167 bp. The deduced amino acid sequence identifies the protein as a novel type of starch synthase from potato with a molecular mass of 139.2 kDa for the immature enzyme including its transit peptide. This novel isoform was designated SS III. An analysis of the expression pattern of the gene indicates that SS III is equally expressed in tubers of different developmental stages as well as in sink and source leaves. In several independent transgenic potato lines, where the expression of SS III was repressed using the antisense approach, the activity of a specific starch synthase isoform was reduced to non-detectable levels as determined through activity staining after native gel electrophoresis. The reduction of this isoform of starch synthase leads to the synthesis of a structurally modified starch in the transgenic plants: there is a drastic change in granule morphology and an increased level of covalently linked phosphate.

Amino Acid Sequence↗
PubMed2003

Decreased sucrose content triggers starch breakdown and respiration in stored potato tubers (Solanum tuberosum).

To change the hexose-to-sucrose ratio within phloem cells, yeast-derived cytosolic invertase was expressed in transgenic potato (Solanum tuberosum cv. Desirée) plants under control of the rolC promoter. Vascular tissue specific expression of the transgene was verified by histochemical detection of invertase activity in tuber cross-sections. Vegetative growth and tuber yield of transgenic plants was unaltered as compared to wild-type plants. However, the sprout growth of stored tubers was much delayed, indicating impaired phloem-transport of sucrose towards the developing bud. Biochemical analysis of growing tubers revealed that, in contrast to sucrose levels, which rapidly declined in growing invertase-expressing tubers, hexose and starch levels remained unchanged as compared to wild-type controls. During storage, sucrose and starch content declined in wild-type tubers, whereas glucose and fructose levels remained unchanged. A similar response was found in transgenic tubers with the exception that starch degradation was accelerated and fructose levels increased slightly. Furthermore, changes in carbohydrate metabolism were accompanied by an elevated level of phosphorylated intermediates, and a stimulated rate of respiration. Considering that sucrose breakdown was restricted to phloem cells it is concluded that, in response to phloem-associated sucrose depletion or hexose elevation, starch degradation and respiration is triggered in parenchyma cells. To study further whether elevated hexose and/or hexose-phosphates or decreased sucrose levels are responsible for the metabolic changes observed, sucrose content was decreased by tuber-specific expression of a bacterial sucrose isomerase. Sucrose isomerase catalyses the reversible conversion of sucrose into palatinose, which is not further metabolizable by plant cells. Tubers harvested from these plants were found to accumulate high levels of palatinose at the expense of sucrose. In addition, starch content decreased slightly, while hexose levels remained unaltered, compared with the wild-type controls. Similar to low sucrose-containing invertase tubers, respiration and starch breakdown were found to be accelerated during storage in palatinose-accumulating potato tubers. In contrast to invertase transgenics, however, no accumulation of phosphorylated intermediates was observed. Therefore, it is concluded that sucrose depletion rather than increased hexose metabolism triggers reserve mobilization and respiration in stored potato tubers.

Cell Respiration↗
PubMed2004

Activities of key enzymes in sucrose-to-starch conversion in wheat grains subjected to water deficit during grain filling.

This study tested the hypothesis that a controlled water deficit during grain filling of wheat (Triticum aestivum) could accelerate grain-filling rate through regulating the key enzymes involved in Suc-to-starch pathway in the grains. Two high lodging-resistant wheat cultivars were field grown. Well-watered and water-deficit (WD) treatments were imposed from 9 DPA until maturity. The WD promoted the reallocation of prefixed 14C from the stems to grains, shortened the grain-filling period, and increased grain-filling rate or starch accumulation rate (SAR) in the grains. Activities of Suc synthase (SuSase), soluble starch synthase (SSS), and starch branching enzyme (SBE) in the grains were substantially enhanced by WD and positively correlated with the SAR. ADP Glc pyrophosphorylase activity was also enhanced in WD grains initially and correlated with SAR with a smaller coefficient. Activities of granule-bound starch synthase and soluble and insoluble acid invertase in the grains were less affected by WD. Abscisic acid (ABA) content in the grains was remarkably enhanced by WD and very significantly correlated with activities of SuSase, SSS, and SBE. Application of ABA on well-watered plants showed similar results as those by WD. Spraying with fluridone, an ABA synthesis inhibitor, had the opposite effect. The results suggest that increased grain-filling rate is mainly attributed to the enhanced sink activity by regulating key enzymes involved in Suc-to-starch conversion, especially SuSase, SSS, and SBE, in wheat grains when subjected to a mild water deficit during grain filling, and ABA plays a vital role in the regulation of this process.

Desiccation↗