Sucrose Transformation Research Articles

Soft drinks. Organoleptic analysis — a criterion for substantiation of expiry dates of products

The paper considers the topicality of the development of methodological approaches to the method for accelerated aging of soft drinks on the market. Selection principles for the controlled indicators that essentially influence finished product quality are presented and the method for sample processing that allows modeling conditions of product spoilage is examined. The investigations enabled establishing the most important criteria (acetaldehyde content, sucrose transformation, CO2 concentration, organoleptic indicators) that allow predicting expiry dates of soft drinks by express methods. The comparative assessment of quality and safety of soft drinks in the conditions of “accelerated” and “natural” aging (over the shelf life with regard to the reserve ratio) by the selected criteria was carried out. The criteria parameters for tasting assessment of soft drinks that allow more correct assessment of nuance descriptors of a product were developed. It is shown that cyclic impact of temperature regimes (warmth 50 °C / cold 6 °C) during the exposure time of 30 days enables modeling soft drink storage over the shelf-life of 12 months in the conditions of natural aging. In this study, the expiry date was confirmed for the studied soft drinks based on plant raw materials and was established for drinks based on flavoring agents.

Soil Available Phosphorus Deficiency Reduces Boll Biomass and Lint Yield by Affecting Sucrose Metabolism in Cotton-Boll Subtending Leaves

Soil available phosphorus (AP) deficiency and shortage of phosphate rocks limit cotton production in China. Therefore, pool-culture experiments were conducted in 2019 and 2020 using two cotton cultivars (CCRI-79, low-P tolerant; SCRC-28, low-P sensitive) under three soil AP levels (P0: 3 ± 0.5, P1: 6 ± 0.5, and P2 (control): 15 ± 0.5 mg kg−1) to ascertain the effect of soil AP on boll biomass and lint yield. P0 and P1 decreased the P concentration and net photosynthetic rate (Pn) of subtending leaves, thus, reducing boll biomass and lint yield. Additionally, soil AP deficiency decreased boll wall:boll, lint:boll, and lint:seed, and increased seed:boll ratio. Upper fruiting branch positions (FB9–12) had higher lint:seed ratio and proportion of the total lint yield under low soil AP. Moreover, soil AP deficiency also reduced the sucrose transformation rate (Tr) and activities of sucrose-metabolizing enzymes, such as ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), sucrose phosphate synthase (SPS), and sucrose synthase (SuSy), while increased carbohydrate levels (soluble sugar, sucrose, and starch) and the activity of cytosolic fructose-1,6-bisphosphatase (cy-FBPase) in the subtending leaves. The sucrose and starch contents, cy-FBPase, and SPS activities of SCRC-28 were more sensitive to low soil AP than CCRI-79. Higher Tr and activities of initial Rubisco and SuSy in the subtending leaves improved boll biomass and lint yield.

Conversion of sugars to methyl lactate with exfoliated layered stannosilicate UZAR-S4

Biomass has been shown as an alternative to fossil fuels for obtaining chemicals. In this work, the transformation of sugars into methyl lactate (ML) at 160 °C was carried out using the layered stannosilicate UZAR-S3 (University of Zaragoza-solid number 3) and the delaminated material UZAR-S4 (University of Zaragoza-solid number 4) obtained from its exfoliation. The exfoliation of UZAR-S3 to UZAR-S4 increased the accessibility of the compounds to the catalytic sites and the medium-strength acidity. Thus, the yield to ML for sucrose transformation increased from 8% for UZAR-S3 to 49.9 % for UZAR-S4. In the reusability tests, the UZAR-S4 catalyst was characterized before and after reaction by several techniques such as X-ray diffraction, thermogravimetry analysis, scanning electronic microscopy, energy dispersive X-ray spectroscopy and nitrogen adsorption. A deactivation of the catalyst was observed, which was related to carbonaceous deposits that decreased the specific surface area and the pore volume of the catalyst.

Enzyme-mediated metabolism in nutritive tissues of galls induced by Ditylenchus gallaeformans (Nematoda: Anguinidae).

The galls induced by Ditylenchus gallaeformans (Nematoda) on leaves of Miconia albicans have unique features when compared to other galls. The nematode colonies are surrounded by nutritive tissues with promeristematic cells, capable of originating new emergences facing the larval chamber, and providing indeterminate growth to these galls. Considering enzyme activity as essential for the translocation of energetic molecules from the common storage tissue (CST) to the typical nutritive tissue (TNT), and the major occurrence of carbohydrates in nematode galls, it was expected that hormones would mediate sink strength relationships by activating enzymes in indeterminate growth regions of the galls. Histochemical, immunocytochemical and quantitative analyses were made in order to demonstrate sites of enzyme activity and hormones, and comparative levels of total soluble sugars, water soluble polysaccharides and starch. The source-sink status, via carbohydrate metabolism, is controlled by the major accumulation of cytokinins in totipotent nutritive cells and new emergences. Thus, reducing sugars, such as glucose and fructose, accumulate in the TNT, where they supply the energy for successive cycles of cell division and for nematode feeding. The histochemical detection of phosphorylase and invertase activities indicates the occurrence of starch catabolism and sucrose transformation into reducing sugars, respectively, in the establishment of a gradient from the CST towards the TNT. Reducing sugars in the TNT are important for the production of new cell walls during the indeterminate growth of the galls, which have increased levels of water-soluble polysaccharides that corroborate such a hypothesis. Functional relationship between plant hormone accumulation, carbohydrate metabolism and cell differentiation in D.gallaeformans-induced galls is attested, providing new insights on cell development and plant metabolism.

Mepiquat chloride effects on potassium acquisition and functional leaf physiology as well as lint yield in highly dense late-sown cotton

Incredible accomplishments have been achieved in agricultural production in China, but many demanding challenges for ensuring sustainable cotton production remain. An efficient cropping model characterized with late sowing, higher density and low fertilizer application is a promising alternative to cope with the present high cost cotton production. However, it is not confirm that mepiquat chloride (MC) application is still required in this new planting model. We hypothesized that MC application might reduce lint yield and thus not be necessary in this new system. A 2-year (2015–2016) field experiment was performed to test this hypothesis in which cotton was planted in mid-May at 10 plants m−2 and with single fertilizer application (225 kg N ha-1). MC was sprayed thrice with 5 leaf intervals initiated from the 6th leaf stage in 5 different dosages i.e. 0 (control), 30, 60, 90, and 120 g ha-1. Morphological attributes viz. plant height, main stem diameter, number of fruiting branches, main stem nodes, main stem green leaves and main stem internode length were evidently reduced by 9–40%, 2–13%, 2–11%, 4–27%, 6–24% and 3–19%, respectively. Cotton potassium accumulation was not significantly influenced; specifically the uptake in reproductive organs from MC0 to MC120 of 45 to 44 kg K ha-1 in MC treated plants averaged across two years. Photosynthesis was reduced by 1–26% due to diminished Rubisco activity by 3–37% in MC treated plants and lint yield decreased by 5–27% as MC dosage increased. Furthermore, alpha amylase, beta amylase and total amylase activities were decreased by 2–16%, 3–19% and 1–17% but sucrose transformation rate was increased in the 4th functional leaf from the apex, respectively. Our data suggest that increased accumulation of sucrose and starch in the leaf with reduced photosynthesis, Rubisco and amylase activity could explain the yield loss. Conclusively, MC application is not needed for this new cotton planting model in Yangtze River Valley of China.

Effects of long‐term elevation of air temperature on sucrose metabolism in cotton leaves at different positions

AbstractGlobal warming could possibly increase the air temperature by 1.8–4.0°C in the coming decade. To forecast the effects of long‐term elevation of air temperature on sucrose synthesis in cotton leaves at different positions, field experiments with the treatments of ambient temperature (control) and elevated temperature (2–3°C) across cotton's boll forming stage were conducted in 2011 and 2012. Results showed that sucrose content in the fourth main‐stem leaves from the terminal (FMLT) during 10–17 days after treatment (DAT) and in the leaves subtending the cotton boll (LSCB) during 17–45 days post‐anthesis (DPA) was lower in the increased temperature treatment than control treatment, but starch content was higher, resulting in higher specific leaf weight (SLW). Lower sucrose content might be attributed to low ribulose‐1,5‐bisphosphate carboxylase‐oxygenase (Rubisco) and cytosolic fructose‐1,6‐bisphosphatase (cy‐FBPase) activities under elevated temperature for all tested leaves. Comparison of different fruiting branch (FB) positions, sucrose transformation rate just decreased in LSCB growing on FB2–3 and FB6–7. Compared with FB10–11, the leaves at FB2–3 and FB6–7 were more sensitive to the increased temperature, showing as that the changing amplitudes of SLW, sucrose content, starch content, initial Rubisco activity and cy‐FBPase activity were greater. Regarding different types of cotton leaves, the effects of elevated temperature on sucrose content, starch content and initial Rubisco activity in FMLT were obvious at the early stage (10–17 DAT), but were not obvious at the late stage. However, the effects were consistent in LSCB from 17 to 45 DPA. In addition, long‐term elevated temperature had smaller impacts on above indices in FMLT than LSCB. Sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) activities were decreased by elevated temperature in FMLT at the early stage, but were increased in LSCB, suggesting that SPS and SuSy were the key enzymes between FMLT and LSCB in response to elevated temperature.

Quantifying Reactive Transport Processes Governing Arsenic Mobility after Injection of Reactive Organic Carbon into a Bengal Delta Aquifer.

Over the last few decades, significant progress has been made to characterize the extent, severity, and underlying geochemical processes of groundwater arsenic (As) pollution in S/SE Asia. However, comparably little effort has been made to merge the findings into frameworks that allow for a process-based quantitative analysis of observed As behavior and for predictions of its long-term fate. This study developed field-scale numerical modeling approaches to represent the hydrochemical processes associated with an in situ field injection of reactive organic carbon, including the reductive dissolution and transformation of ferric iron (Fe) oxides and the concomitant release of sorbed As. We employed data from a sucrose injection experiment in the Bengal Delta Plain to guide our model development and to constrain the model parametrization. Our modeling results illustrate that the temporary pH decrease associated with the sucrose transformation and mineralization caused pronounced, temporary shifts in the As partitioning between aqueous and sorbed phases. The results also suggest that while the reductive dissolution of Fe(III) oxides reduced the number of sorption sites, a significant fraction of the released As was rapidly scavenged through coprecipitation with neo-formed magnetite. These secondary reactions can explain the disparity between the observed Fe and As behavior.

Effects of Soil Salinity on Sucrose Metabolism in Cotton Leaves.

This study investigated sucrose metabolism of the youngest fully expanded main-stem leaf (MSL) and the subtending leaf of cotton (Gossypium hirsutum L.) boll (LSCB) of salt-tolerant (CCRI-79) and salt-sensitive (Simian 3) cultivars and its relationship to boll weight under low, medium and high soil salinity stress in Dafeng, China, in 2013 and 2014. The results showed that with increased soil salinity, 1) both the chlorophyll content and net photosynthetic rate (Pn) decreased, while the internal CO2 concentration firstly declined, and then increased in the MSL and LSCB; 2) carbohydrate contents in the MSL reduced significantly, while sucrose and starch contents in the LSCB increased, as did the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) in both the MSL and LSCB; 3) but invertase activity in both the MSL and LSCB did not change significantly. Our study also showed that the LSCB was more sensitive to soil salinity than was the MSL. Of the measured physiological indices, higher SPS activity, mainly controlled by sps3, may contribute to adaption of the LSCB to soil salinity stress because SPS is beneficial for efficiently sucrose synthesis, reduction of cellular osmotic potential and combined actions of Pn, and sucrose transformation rate and SPS may contribute to the reduction in boll weight under soil salinity stress.

Effects of Soil Salinity on Sucrose Metabolism in Cotton Fiber.

Cotton (Gosspium hirsutum L.) is classified as a salt tolerant crop. However, its yield and fiber quality are negatively affected by soil salinity. Studies on the enzymatic differences in sucrose metabolism under different soil salinity levels are lacking. Therefore, field experiments, using two cotton cultivars, CCRI-79 (salt-tolerant) and Simian 3 (salt-sensitive), were conducted in 2013 and 2014 at three different salinity levels (1.15 dS m-1 [low soil salinity], 6.00 dS m-1 [medium soil salinity], and 11.46 dS m-1 [high soil salinity]). The objective was to elucidate the effects of soil salinity on sucrose content and the activity of key enzymes that are related to sucrose metabolism in cotton fiber. Results showed that as the soil salinity increased, cellulose content, sucrose content, and sucrose transformation rate declined; the decreases in cellulose content and sucrose transformation rate caused by the increase in soil salinity were more in Simian 3 than those in CCRI-79. With increase in soil salinity, activities of sucrose metabolism enzymes sucrose phophate synthase (SPS), acidic invertase, and alkaline invertase were decreased, whereas sucrose synthase (SuSy) activity increased. However, the changes displayed in the SuSy and SPS activities in response to increase in soil salinity were different and the differences were large between the two cotton cultivars. These results illustrated that suppressed cellulose synthesis and sucrose metabolism under high soil salinity were mainly due to the change in SPS, SuSy, and invertase activities, and the difference in cellulose synthesis and sucrose metabolism in fiber for the two cotton cultivars in response to soil salinity was determined mainly by both SuSy and SPS activities.

Potassium application affects carbohydrate metabolism in the leaf subtending the cotton (Gossypium hirsutum L.) boll and its relationship with boll biomass

Field experiments were conducted in 2012 and 2013 with two cotton (Gossypium hirsutum L.) cultivars (Simian 3, low-K tolerant; Siza 3, low-K sensitive) under three levels of potassium (K) fertilization (0, 150 and 300kgK2Oha−1). Results showed that K application increased leaf K concentration, net photosynthetic rate (Pn), stomatal conductance (Gs), plant biomass and stimulated boll biomass (capsule wall, seed and lint biomass). K application increased the proportion of lint biomass, decreased the proportion of seed biomass, and did not affect the proportion of capsule wall biomass. Specific leaf weight (SLW), maximum/minimum sucrose contents and nonstructural carbohydrate (hexose, sucrose, starch) decreased, but sucrose transformation rate in LSCB increased in both cultivars after K application, the leaf critical K levels for hexose content, sucrose content and starch content were 1.1%, 1.3%, 1.2–1.4% in Simian 3 and were 1.6%, 1.7% and 1.7–1.8% in Siza 3, respectively. The activities of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), cytosolic fructose-1,6-bisphosphatase (cy-FBPase), sucrose phosphate synthase (SPS), sucrose synthase (SuSy) and amylase activities increased by K application, whereas soluble acid invertase (SAI) activity decreased. SPS and SuSy activities in Siza 3 were more sensitive than that in Simian 3. Correlation analysis revealed that higher Pn, sucrose transformation rate and SPS activity in LSCB were necessary to improve boll biomass, but the accumulation of sucrose in LSCB was not beneficial to boll biomass.

Waterlogging during flowering and boll forming stages affects sucrose metabolism in the leaves subtending the cotton boll and its relationship with boll weight

The work explored sucrose metabolism in the leaves subtending the cotton boll (SBL) and its role in boll weight after waterlogging in cotton. Results showed that net photosynthesis rate (Pn), relative water content, contents of Chlorophyll a and Chlorophyll b, initial ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) activity and cytosolic fructose-1, 6-bisphosphatase (cy-FBPase) activity decreased with waterlogging in the SBL on fruiting branches 2–3 (FB2–3) and FB6–7. Activities of sucrose synthase (SuSy) and sucrose phosphate synthase (SPS) increased to the maximum up to 6 days of waterlogging then decreased with prolonged waterlogging. Rubisco activation and specific leaf weight increased and gene expressions of SuSy, SPS and rubisco activase (RCA) were all up-regulated with the duration of waterlogging, especially for the SBL on FB6–7. The induction of activity and gene expression of SuSy was most significant indicating its crucial role in sucrose metabolism after waterlogging. For the SBL in the later period of boll development on upper FB10–11 and FB14–15, the pattern seemed opposite to that of FB2–3 and FB6c7 as compensation effect in vegetative growth existed. Correlation analysis revealed that initial Rubisco activity and cy-FBPase activity were the main limitation to Pn reduction after waterlogging. Reduction in Pn, sucrose transformation rate and initial Rubisco activity directly decrease boll weight in waterlogged cotton. Besides the role in sucrose metabolism after waterlogging, SuSy also had a positive significant correlation with the duration of rapid-accumulation period for seed fiber weight (P<0.05). These findings elucidated mechanisms to waterlogging that affected seed fiber weight, which resulted from alteration in carbohydrates, enzymes and genes.

The Effects of Fruiting Positions on Cellulose Synthesis and Sucrose Metabolism during Cotton (Gossypium hirsutum L.) Fiber Development

Cotton (Gossypium hirsutum L.) boll positions on a fruiting branch vary in their contribution to yield and fiber quality. Fiber properties are dependent on deposition of cellulose in the fiber cell wall, but information about the enzymatic differences in sucrose metabolism between these fruiting positions is lacking. Therefore, two cotton cultivars with different sensitivities to low temperature were tested in 2010 and 2011 to quantify the effect of fruit positions (FPs) on fiber quality in relation to sucrose content, enzymatic activities and sucrose metabolism. The indices including sucrose content, sucrose transformation rate, cellulose content, and the activities of the key enzymes, sucrose phosphate synthase (SPS), acid invertase (AI) and sucrose synthase (SuSy) which inhibit cellulose synthesis and eventually affect fiber quality traits in cotton fiber, were determined. Results showed that as compared with those of FP1, cellulose content, sucrose content, and sucrose transformation rate of FP3 were all decreased, and the variations of cellulose content and sucrose transformation rate caused by FPs in Sumian 15 were larger than those in Kemian 1. Under FP effect, activities of SPS and AI in sucrose regulation were decreased, while SuSy activity in sucrose degradation was increased. The changes in activities of SuSy and SPS in response to FP effect displayed different and large change ranges between the two cultivars. These results indicate that restrained cellulose synthesis and sucrose metabolism in distal FPs are mainly attributed to the changes in the activities of these enzymes. The difference in fiber quality, cellulose synthesis and sucrose metabolism in response to FPs in fiber cells for the two cotton cultivars was mainly determined by the activities of both SuSy and SPS.

Changes of sucrose metabolism in leaf subtending to cotton boll under cool temperature due to late planting

Because reproductive growth could be influenced by sucrose metabolism of major source leaf (leaf subtending to cotton boll, LSCB), we hypothesized that decreased temperatures under field conditions would limit morphology and biomass distributions of the whole cotton plant by decreasing photosynthesis of LSCB and inhibiting sucrose metabolism in LSCB. To address this hypothesis, two cotton cultivars, Kemian 1 and Sumian 15, were grown at three planting dates (25 April, 25 May and 10 June) in 2009–2011 to obtain LSCB and bolls exposed to contrasting ambient temperatures while at the same developmental stage (white flowers on the first position of 6–7th fruiting branches). Sample collection and measurement were conducted during boll development at MDTmin of 25.9°C and 24.0°C for the early planting date of 25 April (optimal planting date in the Yangtze River Valley), 20.4°C and 18.4°C for the 25 May planting date, and 16.5°C and 16.0°C for the 10 June planting date in 2010 and 2011, respectively. Microclimate measurements included photosynthetic active radiation, relative humidity and air temperature. Late planting decreased boll number, boll weight, LAI, total biomass and harvest index (P<0.05), but increased leaf to shoot, leaf to stem and leaf to boll ratios. Cool temperature increased SLW and carbohydrate contents in LSCB, but decreased Pn and sucrose transformation rate in LSCB (P<0.05). Under cool temperatures (MDTmin of 20.4°C and 16.5°C in 2010, and 18.4°C and 16.0°C in 2011 during boll development) in the late planting dates (25 May and/or 10 June), the activities of Rubisco and cytosolic fructose-1,6-bisphosphatase (cy-FBPase) increased, whereas sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) activities decreased, and their peak values were delayed. The variability of Pn, SPS activity, sucrose transformation rate in LSCB and boll weight under cool temperature for Sumian 15 was greater than those of Kemian 1. In addition, there was a significantly positive correlation between Pn and SPS in LSCB, as well as SPS and boll weight in 2010 and 2011 (P<0.05). It is concluded that, of the measured physiological and reproductive processes, the difference of sucrose metabolizing enzymes in LSCB for the two cotton cultivars under cool temperature due to late planting were mainly determined by SPS activity, while higher Pn and SPS in LSCB were necessary to improve boll weight. However, greater boll weight does not necessarily need high Pn, SPS and SuSy activities, and great sucrose transformation rate in LSCB.

Effect of 6-BA and ABA Applications on Yield, Quality and Photosynthate Contents in the Subtending Leaf of Cotton with Different Planting Dates

To study the effects of 6-BA and ABA applications on carbohydrate contents and endogenous hormones in subtending leaf, and their relationship to cotton yield and quality under different planting dates, we conducted a field experiment with two cotton cultivars Kemian 1 and NuCOTN 33B in the Lower Reaches of Yangtze River (Nanjing) and in the Yellow River Valley (Anyang), China. The cotton seeds were planted on Apr. 25th and May 25th, 2006, respectively, which could result in different growth temperatures for the bolls and their subtending leaves at the same site, and the growth regulators were sprayed at flowering stage. The results showed that the application of 6-BA significantly increased contents of sucrose and starch, and sucrose transformation rate in the subtending leaf, while the application of ABA only regulated the balance of endogenous hormones. The application of 6-BA increased boll weight and enhanced fiber qualities in cotton plants with planting dates of Apr. 25th and May 25th, whereas the decrease ranges of cotton yield and quality in Anyang were less for the application of ABA in cotton plants with planting date of May 25th, compared to those with planting date of Apr. 25th. However, the seed quality was not affected by the applications of 6-BA or ABA significantly. The application of 6-BA or ABA improved relative cotton quality of late planted cotton, whereas the action mechanisms were different. The application of 6-BA improved cotton yield and quality via enhancing the photosynthate contents and sucrose transformation rate. However, the application of ABA improved cotton yield and quality via in- creasing the stress resistance of cotton plants.

Physiological and biochemical dissection of fiber development in colored cotton

Colored cotton is a very attractive proposition for the textile industry as it reduces the cost for dying. However, inferior fiber quality and non uniform color make it unsuitable for heavy machine spinning. Due to this reason cultivation of colored cotton on commercial scale has been restricted by cotton growers. The current study was planned to unveil the process of fiber development in isogenic lines of brown, green and white cotton by comparing their fiber length, flavonoid, cellulose, carbohydrate and enzyme activities (SuSy, SPS, acid invertase, Cox, NAD+, NADH, NADP+, and NADPH). White cotton fiber exhibited high cellulose contents (915.81 mg g−1) and long fibers (3.07 cm) as compared to colored cotton fibers with low cellulose content (787.63 and 780.66 mg g−1) and shorter fiber length (2.54 and 2.48 cm). Similarly the amount of flavonoids also varied significantly with maximum concentration (8.67 and 7.13 mg g−1) in brown and green cotton fiber at 5 DPA as compared to white cotton fiber (3.12 mg g−1) at 0 DPA. This high concentration of flavonoid not only lowered the total amount of carbohydrates but also lowered the sucrose transformation rate to developing cotton fiber in colored cotton. The activity of different enzymes (AI, SuSy and SPS, Cox, NAD+/NADH and coenzymes NADP+/NADPH involved in the metabolism of carbohydrates was higher in brown cotton fiber than green cotton fiber. However, high activity of these enzymes did not always correlated with higher amount of cellulose thus indicated the involvement of complex mechanisms for cellulose and flavonoid synthesis during the development of cotton fiber.

Application of a SUGAR model to analyse sugar accumulation in peach cultivars that differ in glucose–fructose ratio

SUMMARYA SUGAR model, which was established to predict the partitioning of carbon into sucrose, glucose, fructose and sorbitol in fruit mesocarp of peach cultivars (Prunus persica (L.) Batch) with normal glucose: fructose ratio (G:F) of 0·8–1·5, was evaluated and extended for peach cultivars with a high G:F ratio of 1·5–7·8. The extended model (SUGARb) is more generic and assumes a high G:F ratio to be due to preferential transformation of sorbitol into glucose, preferential utilization of fructose or preferential conversion of fructose into glucose. The simulated seasonal variations in sugars via the SUGARb-model-matched experimental data for three normal and three high G:F cultivars well, and accurately exhibited G:F ratio characteristics. The relative rates of sucrose transformation into glucose and fructose differed according to cultivar but not according to G:F status. Compared with hexosephosphate interconversion, a lower production rate of fructose than glucose from sorbitol, and/or a higher utilization rate of fructose than that of glucose might be preferential alternatives for forming high G:F ratios in the high G:F cultivars studied in the present study, which is discussed in the light of recent results on enzyme activities.

Sucrose metabolism in cotton ( Gossypium hirsutum L.) fibre under low temperature during fibre development

The effects of low temperature on sucrose content and activities of key enzymes related to sucrose metabolism in cotton ( Gossypium hirsutum L.) fibre were investigated. Two cotton cultivars, Kemian 1 and Sumian 15, were grown in the field at two sowing dates in 2006 and three sowing dates in 2007, the differences of environmental conditions during fibre development period (from flowering date to boll opening date) for different sowing dates were primarily on temperature. Low temperatures (MDTmin of 21.1, 20.5 and 18.1 °C) in late sowing dates (25 May/10 June) prolonged the fibre development period, and had significant effect on cellulose synthesis and sucrose metabolism. Results showed that, under low temperature, sucrose content was increased, cellulose content and sucrose transformation rate were decreased, and the variability of cellulose content and sucrose transformation rate through sowing dates in Sumian 15 was more than that in Kemian 1. The measurable activities of sucrose phosphate synthase (SPS), sucrose synthase (SuSy) and acid/alkaline invertases in sucrose metabolism were affected by low temperatures. Under low temperatures, activities of SuSy and invertase in sucrose degradation were increased, and two cultivars had the similar change. In contrast, the activity of SPS in sucrose synthesis was lower than the activity in developing fibre at normal environmental condition, and the time to peak activity was delayed, SPS activity in response to temperatures differed between two cultivars. The results indicated that restrained cellulose synthesis and sucrose metabolism under low temperature were mainly attributed to the changed activities of enzymes (SPS, SuSy and invertase), and the difference of cellulose synthesis and sucrose metabolism in response to temperature in fibre cells for two cotton cultivars was mainly determined by the level of SPS activity.

Isolation and enzymic properties of levansucrase secreted by Acetobacter diazotrophicus SRT4, a bacterium associated with sugar cane

Acetobacter diazotrophicus, a nitrogen-fixing bacterium associated with sugar cane, secretes a levansucrase (sucrose-2,6-beta-D-fructan 6-beta-D-fructosyltransferase; EC 2.4.1.10). This enzyme is constitutively expressed and represents more than 70% of the total proteins secreted by strain SRT4. The purified protein consists of a single 58 kDa polypeptide with an isoelectric point of 5.5. Its activity is optimal at pH 5.0. It catalyses transfructosylation from sucrose to a variety of acceptors including water (sucrose hydrolysis), glucose (exchange reaction), fructan (polymerase reaction) and sucrose (oligofructoside synthesis). In vivo the polymerase activity leads to synthesis of a high-molecular-mass fructan of the levan type. A. diazotrophicus levansucrase catalyses transfructosylation via a Ping Pong mechanism involving the formation of a transient fructosyl-enzyme intermediate. The catalytic mechanism is very similar to that of Bacillus subtilis levansucrase. The kinetic parameters of the two enzymes are of the same order of magnitude. The main difference between the two enzyme specificities is the high yield of oligofructoside, particularly 1-kestotriose and kestotetraose, accumulated by A. diazotrophicus levansucrase during sucrose transformation. We discuss the hypothesis that these catalytic features may serve the different biological functions of each enzyme.

Immobilisation of levansucrase on calcium phosphate gel strongly increases its polymerase activity

The catalytic properties of levansucrase bound to hydroxyapatite were studied as a possible model for enzyme behaviour when associated in vivo to matrices such as the cell wall of bacteria or tooth surfaces. The activity of the immobilised enzyme was mainly directed towards its polymerase activity. The yield of levan reached 85%. The k cat of the enzyme for sucrose transformation was increased and the K m for this substrate was unmodified. These properties allow the design of a system for the large-scale production of high-molecular-weight branched-chain levan in vitro in high yield.

Starch‐Sugar Transformation During Banana Ripening: The Behavior of UDP Glucose Pyrophosphorylase, Sucrose Synthetase and Invertase

ABSTRACTStarch concentration, sequence of appearance of sucrose, glucose and fructose and activity of some enzymes of sucrose synthesis were followed during ripening of preclimacteric bananas (Musa acuminatd). As starch was degraded sucrose content increased and preceded formation of glucose and fructose. At the same time, while UDP‐glucose pyrophosphorylase activity remained constant, activity of sucrose synthetase and invertase increased. The observed sugar and enzyme changes indicated that starch to sucrose transformation via glucose‐1‐phosphate‐UDP‐glucose may be an important mechanism for starch disappearance during ripening. The hypothesis was confirmed with thin banana slices infiltrated with [14C(U)]glucose‐1‐phosphate: the label was incorporated into sucrose three times faster for climacteric than for preclimacteric fruits. Pyrophosphorylase activity and climacteric induced activation of sucrose synthetase could be inhibited by protein and nucleic acids synthesis inhibitors.