Sucrose Phosphate Synthase Activity Research Articles

Time Course of Starch Biosynthesis Enzymes Activity and Root Tuber Starch of Four Cassava Cultivars

To understand the accumulation rule of cassava root tuber starch, the amylose, amylopectin and total starch content of fresh root tuber, the enzyme activities of sucrose synthase (SuS, EC 2.4.1.13) and sucrose phosphate synthase (SPS, EC 2.4.1.14) of leaves, the enzyme activities of ADP-glucose pyrophosphorylase (AGPase, EC 2.7.7.27), soluble starch synthase (SSS, EC 2.4.1.21) and starch branching enzyme (SBE, EC. 2.4.1.18) of tubers were assessed by using cultivars SC201, SC205, GR891 and GR911 leaves and root tubers during their growth period, respectively. The results as follows: the enzyme activity of leaf SPS and the synthesis direction of SuS showed the highest at August, 2010, however the enzyme activity of the decomposing direction of SuS formed parabolic curve; the enzyme activity of tuber AGPase showed an increased then decreased single peak curve, the enzyme activity of tuber SSS oscillating decreased, while the enzyme activity of SBE was relatively stable; the amylose, amylopectin and total starch contents of fresh cassava tuber were all gradually increased along with the growth period. This research would enrich our knowledge of the time course of amylose, amylopectin and total starch contents of fresh cassava tuber, and above related enzyme activities.

Mycorrhizas alter sucrose and proline metabolism in trifoliate orange exposed to drought stress

Arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in plants, whereas little is known regarding AMF contribution to sucrose and proline metabolisms under drought stress (DS). In this study, Funneliformis mosseae and Paraglomus occultum were inoculated into trifoliate orange (Poncirus trifoliata) under well watered and DS. Although the 71-days DS notably (P < 0.05) inhibited mycorrhizal colonization, AMF seedlings showed significantly (P < 0.05) higher plant growth performance and leaf relative water content, regardless of soil water status. AMF inoculation significantly (P < 0.05) increased leaf sucrose, glucose and fructose concentration under DS, accompanied with a significant increase of leaf sucrose phosphate synthase, neutral invertase, and net activity of sucrose-metabolized enzymes and a decrease in leaf acid invertase and sucrose synthase activity. AMF inoculation produced no change in leaf ornithine-δ-aminotransferase activity, but significantly (P < 0.05) increased leaf proline dehydrogenase activity and significantly (P < 0.05) decreased leaf both Δ1-pyrroline-5-carboxylate reductase and Δ1-pyrroline-5-carboxylate synthetase activity, resulting in lower proline accumulation in AMF plants under DS. Our results therefore suggest that AMF strongly altered leaf sucrose and proline metabolism through regulating sucrose- and proline-metabolized enzyme activities, which is important for osmotic adjustment of the host plant.

Potassium fertilizer improves drought stress alleviation potential in cotton by enhancing photosynthesis and carbohydrate metabolism

Under drought, limited photo-assimilates synthesis and their poor partitioning is a main constraint to final yield production in cotton (Gossypium hirsutum L.). To study the potassium (K) role in photo-assimilation and carbohydrate metabolism in cotton under soil drought stress during flowering and boll formation stage, a two-year pot experiment was conducted in 2015 and 2016. Two cotton cultivars namely Simian 3 (low-K tolerant) and Siza 3 (low-K sensitive) were grown under three K rates (0, 150 and 300kgK2Oha−1). Plants were exposed to well-watered [(75±5%) soil relative water content (SRWC)] and water stress (35–40% SRWC) for 7days followed by re-watering to SRWC (75±5%). The results showed that water-stressed plants under K0 application exhibited significant decline in net photosynthesis, stomatal conductance, intercellular CO2 concentration and ribulose-1,5-bisphosphate carboxylase (Rubisco) activity and resulting in reduced photo-assimilates synthesis and partitioning towards reproductive organs in both cultivars. Conversely, K application decreased the decline in photosynthesis, Rubisco activity and biomass accumulation and partitioning. The positive effects of K application increased as increasing K rates, and that was more pronounced in Siza 3 than Simian 3. Drought stress decreased starch content but increased sucrose content; whereas, K application maintained higher concentration of sucrose in leaves of water-stressed plants through the regulation of higher sucrose phosphate synthase (SPS), sucrose synthase (SuSy) and lower soluble acid invertase (SAI) activities. The results of the study concluded that K application regulated the photo-assimilation and translocation process along with the related enzymes activities in cotton. The study suggests that K nutrient management strategy has the potential to minimize the impacts of drought stress in cotton.

Integrated Management Strategies Increase Cottonseed, Oil and Protein Production: The Key Role of Carbohydrate Metabolism.

Cottonseed, oil, and protein, as the by-products of cotton production, have the potential to provide commodities to meet the increasing demand of renewable bio-fuels and ruminant feed. An increase in crop yield per unit area requires high-yielding cultivar management with an economic nitrogen (N) rate, an optimal N application schedule, high-yielding plant populations and strong seedlings. Whether the integration of these agronomic practices into a coherent management system can increase the productivity of cotton fiber, embryo oil and protein requires experimental elucidation. In this 2-year study, conventional management practices (CM) were used as a control, and two integrated management strategies (IMS1 and IMS2) were considered at two soil fertility levels (high soil fertility and low soil fertility) to analyze the metabolic and biochemical traits of cotton embryos. The results illustrate that the cottonseed, oil, and protein yields for IMS1 and IMS2 were significantly higher than those under CM at both soil fertility levels and the fiber yield increased as well. The IMS regulated the maternal photo thermal environment by delaying the flowering date, resulting in increases in the seed weight. In developing cotton embryos, the IMS increased the embryo weight accumulation rate and biomass partitioning into oil and protein, which were associated with high activities of H+-ATPase, H+-PPase, sucrose synthase (SuSy), and cell wall invertase (C-INV) and low activities of sucrose phosphate synthase (SPS) and vacuole invertase (V-INV). Increased hexoses (D-fructose, D-glucose) content contributed to the oil and protein contents. These results suggest that increased sucrose/H+ symport, sucrose hydrolysis, hexoses synthesis, and cumulative photo-thermal product (PTP), especially in the early stage of embryo growth, play a dominant role in the high productivity of cotton oil and protein.

Sink activity in Washington navel orange fruit borne on leafy and leafless inflorescences

Washington navel orange (WNO) (Citrus sinensis L. Osbeck) fruit borne on leafy (LY) inflorescences (with leaves) were confirmed to be stronger sinks based on their faster-growth rate during the 9 weeks after petal fall than fruit borne on leafless (LS) inflorescences (without leaves). During this period, the activities of enzymes involved in phloem unloading and sucrose synthesis, including vacuole soluble acid invertase (VINV), sucrose synthase (SuSy), and sucrose phosphate synthase (SPS), were quantified in whole fruit and individual fruit tissues, exocarp (flavedo), mesocarp (albedo), vascular bundles, and endocarp (juice sacs), to identify the determinants of citrus fruit sink strength during Stage I of fruit development. Fruit set on LY and LS inflorescences exhibited no differences in VINV activity during the 9-week period. In contrast, SuSy activity was significantly greater in fruit developing on LY inflorescences, whereas SPS activity was significantly greater in fruit from LS inflorescences. For individual tissues isolated from fruit collected 7 and 9 weeks after petal fall, LY inflorescences had greater SuSy activity in vascular bundles (weeks 7 and 9), flavedo (weeks 7 and 9) and juice sacs (week 9) than fruit of LS inflorescences, whereas fruit from LS inflorescences had greater VINV activity in vascular bundles (week 9), flavedo (week 7) and juice sacs (weeks 7 and 9). The results provide strong evidence that SuSy activity is the determinant of greater sink strength during early development of WNO fruit borne on LY inflorescences.

Melon fruit sugar and amino acid contents are affected by fruit setting method under protected cultivation

This study investigated the effect of different fruit setting methods on fruit quality of melon (Cucumis melo L.) under protected cultivation. The results showed that artificial and honey bee pollination decreased single fruit weight compared with 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) treatment, whereas the lowest value was observed in artificial pollination. Artificial and honey bee pollination apparently increased sucrose content, and the increased activity of sucrose phosphate synthase (SPS) was the key reason. In addition, total content of amino acids (17 kinds) were increased by 31% and 28% in artificial and honey bee-pollinated fruits compared with CPPU treatment, respectively. Honey bee pollination also improved single fruit weight and taste compared with artificial pollination. Therefore, we can conclude that artificial and honey bee pollination can improve the quality of melon fruits. In addition, honey bee can provide a better pollination service compared with artificial pollination for melons grown under protected cultivation systems.

Differences in Sugar Accumulation and Mobilization between Sequential and Non-Sequential Senescence Wheat Cultivars under Natural and Drought Conditions.

Wheat leaf non-sequential senescence at the late grain-filling stage involves the early senescence of younger flag leaves compared to that observed in older second leaves. On the other hand, sequential senescence involves leaf senescence that follows an age-related pattern, in which flag leaves are the latest to undergo senescence. The characteristics of sugar metabolism in two sequential senescence cultivars and two non-sequential senescence cultivars under both natural and drought conditions were studied to elucidate the underlying mechanism of drought tolerance in two different senescence modes. The results showed that compared to sequential senescence wheat cultivars, under natural and drought conditions, non-sequential senescence wheat cultivars showed a higher leaf net photosynthetic rate, higher soluble sugar levels in leaves, leaf sheaths, and internodes, higher leaf sucrose synthase (SS) and sucrose phosphate synthase (SPS) activity, and higher grain SS activity, thereby suggesting that non-sequential senescence wheat cultivars had stronger source activity. Spike weight, grain weight per spike, and 100-grain weight of non-sequential senescence cultivars at maturity were significantly higher than those of sequential senescence cultivars under both natural and drought conditions. These findings indicate that the higher rate of accumulation and the higher mobilization of soluble sugar in the leaves, leaf sheaths and internodes of non-sequential senescence cultivars improve grain weight and drought tolerance. At the late grain-filling stage, drought conditions adversely affected leaf chlorophyll content, net photosynthetic rate, soluble sugar and sucrose content, SS and SPS activity, gain SS activity, and weight. This study showed that higher rates of soluble sugar accumulation in the source was one of the reasons of triggering leaf non-sequential senescence, and higher rates of soluble sugar mobilization during leaf non-sequential senescence promoted high and stable wheat yield and drought tolerance.

Zinc sulfate spray increases activity of carbohydrate metabolic enzymes and regulates endogenous hormone levels in apple fruit

The application of zinc sulfate (ZnSO4) were conducted during two years on fourteen-year-old ‘Fuji’ apple trees before budbreak. The effects of zinc sulfate application on Zn contents, activities of carbohydrate metabolism enzymes, contents of endogenous hormones and carbohydrate in apple fruit at different development stages were investigated. The treatment significantly increased the Zn contents of fruit. The treatment significantly decreased sucrose content of fruit at fruit expansion stage and increased its content of fruit at fruit mature stage; the treatment significantly increased fructose content and glucose at fruit expansion stage and mature stage; the treatment decreased sorbitol at young fruit stage and expansion stage significantly. The activities of sucrose synthase (SS), sorbitol dehydrogenase (SDH) and acid inverts (AI) in fruit of trees treated were significantly higher than the control at young fruit stage and expansion stage. Sucrose phosphate synthase (SPS) activities in fruit of treated trees were significantly higher than that of the control during fruit mature stage. The treatment increased the content of indole acetic acid (IAA) and gibberellin (GA3) in fruit seeds significantly at young fruit stage. The treatment significantly reduced the contents of abscisic acid (ABA) in seeds of fruit at young fruit stage and significantly increased ABA content during fruit mature stage. Spraying ZnSO4 enhanced the fruit Zn content, which resulted in the higher activities of carbohydrate metabolism-related enzymes (SDH, AI, SS, SPS) and regulated IAA, GA3 and ABA levels, contributing to the accumulation of carbohydrate in fruit.

A reduction of sucrose phosphate synthase (SPS) activity affects sucrose/starch ratio in leaves but does not inhibit normal plant growth in rice

Sucrose phosphate synthase (SPS) has been shown to mediate sucrose/starch ratio in plant leaves through studies of ‘starch leaf’ species that mainly accumulate starch in their leaves. However, the contribution of SPS to sucrose/starch ratio in rice leaves, which mainly accumulate sucrose (i.e., ‘sugar leaf’), has not been confirmed due to inconsistencies in the results of previous studies. In this study, we analyzed mutant lines with reduced SPS activity, which were generated using Tos17 insertion, RNAi, and the CRISPR/Cas9 system. The knockdown and knockout mutants of OsSPS1 showed a 29–46% reduction in SPS activity in the leaves, but the carbohydrate content in the leaves and plant growth were not significantly different from those of wild-type plants. In a double knockout mutant of OsSPS1 and OsSPS11 (sps1/sps11), an 84% reduction in leaf SPS activity resulted in higher starch accumulation in the leaves than in the wild-type leaves. However, the sps1/sps11 plants grew normally, which is in contrast to the inhibited growth of SPS mutants of Arabidopsis thaliana, a typical starch leaf plant. These results suggest that SPS has a smaller effect on the sucrose/starch ratio in leaves and growth of rice than on starch leaf species.

Cytokinin-Regulated Sucrose Metabolism in Stay-Green Wheat Phenotype.

A wheat stay-green mutant, tasg1, was observed to exhibit significantly delayed senescence in the late developmental stage. The photosynthetic capacity of the flag leaf was greater in tasg1 than in wild type (WT) plants. In addition, the grain volume of tasg1 was significantly higher than that of WT at the early filling stage. The content of various cytokinins (CKs) in the grain was significantly higher in tasg1 than in WT and was accompanied by an upregulated expression of some cell cycle-related genes. Examination of the metabolism of soluble sugars in tasg1 and WT revealed that the concentrations of glucose (Glu), fructose (Fru), and sucrose (Suc) were higher in the flag leaves and grains of tasg1 than in WT plants. The activities of sucrose-phosphate synthase (SPS), sucrose synthase (SuSy), and cell wall invertase (CW-invertase) were higher in tasg1, suggesting an altered metabolism and transport of soluble sugars. Furthermore, when tasg1 was treated with the CK inhibitor lovastatin, the activity of invertase was inhibited and was associated with premature senescence phenotype. However, the activity of invertase was partially recovered in tasg1 when treated with 6-benzylaminopurine (BAP). The trend of change in the concentrations of Glu, Fru, and Suc was similar to that of invertase. Our results suggest that CKs might regulate the stay-green phenotype of tasg1 by regulating the invertase activity involved in Suc remobilization.

Comparative transcriptome investigation of global gene expression changes caused by miR156 overexpression in Medicago sativa.

BackgroundMedicago sativa (alfalfa) is a low-input forage and potential bioenergy crop, and improving its yield and quality has always been a focus of the alfalfa breeding industry. Transgenic alfalfa plants overexpressing a precursor of alfalfa microRNA156 (MsmiR156) were recently generated by our group. These plants (miR156OE) showed enhanced biomass yield, reduced internodal length, increased shoot branching and trichome density, and a delay in flowering time. Transcripts of three SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) genes (MsSPL6, MsSPL12, and MsSPL13) were found to be targeted for cleavage by MsmiR156 in alfalfa.ResultsTo further illustrate the molecular mechanisms underlying the effects of miR156 in alfalfa, two miR156OE genotypes (A11a and A17) were subjected to Next Generation RNA Sequencing with Illumina HiSeq. More than 1.11 billion clean reads were obtained from our available sequenced samples. A total of 160,472 transcripts were generated using Trinity de novo assembly and 4,985 significantly differentially expressed genes were detected in miR156OE plants A11a and A17 using the Medicago truncatula genome as reference. A total of 17 genes (including upregulated, downregulated, and unchanged) were selected for quantitative real-time PCR (qRT-PCR) validation, which showed that gene expression levels were largely consistent between qRT-PCR and RNA-Seq data. In addition to the established SPL genes MsSPL6, MsSPL12 and MsSPL13, four new SPLs; MsSPL2, MsSPL3, MsSPL4 and MsSPL9 were also down-regulated significantly in both miR156OE plants. These seven SPL genes belong to genes phylogeny clades VI, IV, VIII, V and VII, which have been reported to be targeted by miR156 in Arabidopsis thaliana. The gene ontology terms characterized electron transporter, starch synthase activity, sucrose transport, sucrose-phosphate synthase activity, chitin binding, sexual reproduction, flavonoid biosynthesis and lignin catabolism correlate well to the phenotypes of miR156OE alfalfa plants.ConclusionsThis is the first report of changes in global gene expression in response to miR156 overexpression in alfalfa. The discovered miR156-targeted SPL genes belonging to different clades indicate miR156 plays fundamental and multifunctional roles in regulating alfalfa plant development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3014-6) contains supplementary material, which is available to authorized users.

Effects of late planting and shading on sucrose metabolism in cotton fiber

Effects of cool temperature due to late planting and low light due to shading on sucrose metabolism in cotton fiber were investigated with two cotton cultivars (Kemian 1, cool temperature-tolerant and Sumian 15, cool temperature-sensitive) at two planting dates (the optimized planting date 25 April and the late planting date 10 June) along with two shading levels of crop relative light rate (CRLR) 100% and 60% in 2010 and 2011. Compared with the optimized planting date with CRLR 100% (OPD), the acid invertase (AI) activity was little affected in the optimized planting date with CRLR 60% (OPD-CRLR 60%). The sucrose synthase (SuSy) and sucrose phosphate synthase (SPS) activities were decreased, which would reduce sucrose degradation and recycle, hindering the synthesis of cellulose. However, the sucrose concentration was decreased, which might be because of lower sucrose import from the leaf. The transcript levels of sucrose synthase gene (Susy) and sucrose phosphate synthase gene (SPS) isoforms were decreased. Comparison between the two cultivars, SPS1 was the largest down-regulated isoform in Kemian 1, but SPS2 was the largest down-regulated isoform in Sumian 15. Also, the SPS activity was more sensitive to low light for Kemian 1 than Sumian 15. Although SuSy and AI activities were much higher in the late planting date with CRLR 100% (LPD) than OPD, sucrose concentration was still high. Therefore, a lot of sucrose could not be fluently used in cellulose synthesis, leading to the decrease of cellulose concentration. The transcript levels of the three SPS isoforms increased for both cultivars. The expressions of SusyA, SusyB, and SusyC were increased for Kemian 1, but the expressions of SusyD, SusyA, SusyB, and SusyC were significantly decreased for Sumian 15. In the late planting date with CRLR 60%, no interaction effect between cool temperature and low light was observed in the concentrations of cellulose and sucrose, the activities of SPS and AI and the expression of SPS3, but was found in the transcript levels of SusyB and SPS2 for both cultivars. Also, the interaction effect was observed in the transcript levels of SusyA, SusyC, SusyD and SPS1 in Sumian 15, but was not found in Kemian 1.

Assessment of Suitable Reference Genes for Quantitative Gene Expression Studies in Melon Fruits.

Melon (Cucumis melo L.) is an attractive model plant for investigating fruit development because of its morphological, physiological, and biochemical diversity. Quantification of gene expression by quantitative reverse transcription polymerase chain reaction (qRT-PCR) with stably expressed reference genes for normalization can effectively elucidate the biological functions of genes that regulate fruit development. However, the reference genes for data normalization in melon fruits have not yet been systematically validated. This study aims to assess the suitability of 20 genes for their potential use as reference genes in melon fruits. Expression variations of these genes were measured in 24 samples that represented different developmental stages of fertilized and parthenocarpic melon fruits by qRT-PCR analysis. GeNorm identified ribosomal protein L (CmRPL) and cytosolic ribosomal protein S15 (CmRPS15) as the best pair of reference genes, and as many as five genes including CmRPL, CmRPS15, TIP41-like family protein (CmTIP41), cyclophilin ROC7 (CmCYP7), and ADP ribosylation factor 1 (CmADP) were required for more reliable normalization. NormFinder ranked CmRPS15 as the best single reference gene, and RAN GTPase gene family (CmRAN) and TATA-box binding protein (CmTBP2) as the best combination of reference genes in melon fruits. Their effectiveness was further validated by parallel analyses on the activities of soluble acid invertase and sucrose phosphate synthase, and expression profiles of their respective encoding genes CmAIN2 and CmSPS1, as well as sucrose contents during melon fruit ripening. The validated reference genes will help to improve the accuracy of gene expression studies in melon fruits.

Ethylene inhibited sprouting of potato tubers by influencing the carbohydrate metabolism pathway.

The aim of this study was to investigate the role of ethylene to control sprouting of potatoes by observing the effect of exogenous ethylene on carbohydrate metabolism and key enzymes. The initial time of potato tuber sprouting and sprouting index were recorded, and rate of respiration, total sugar, total reducing sugar, starch, fructose, glucose, sucrose and the activities of acid invertase (AI), neutral invertase (NI), sucrose synthase (SS), sucrose phosphate synthase (SPS), starch phosphorylase and amylase during sprouting were measured. Exogenous ethylene inhibited sprouting of potato tubers. Moreover, exogenous ethylene increased respiration total sugar, AI activity, SPS activity, SS activity, and reduced sugar and assay activity. Nevertheless, starch, glucose, fructose, NI activity and starch phosphorylase activity showed lower variation. Lower sprouting resulted into potatoes with higher levels of total sugar, total reducing sugar and glucose, and lower level of fructose and sucrose. And sprouting could be inhibited by increasing the activities of SS, SPS and AI by treatment with 199.3μlL-1 exogenous ethylene. Overall, exogenous ethylene inhibited sprouting of potato tubers by influencing its carbohydrate metabolism.

Relationship between cellulose accumulation and lodging resistance in the stem of relay intercropped soybean [Glycine max (L.) Merr.

Stem lodging is the most important constraint for soybean at seedling stage in maize–soybean intercropping in China. This study was conducted to determine whether cellulose accumulation and lodging resistance of soybean was affected by different cropping systems and soybean varieties with different shading tolerance at seedling stage. Three soybean varieties – Nandou 032-4 (shade susceptible), Jiuyuehuang (moderately shade tolerant) and Nandou 12 (shade tolerant) – were used to investigate the effect of intercropping on soybean lodging behavior and cellulose accumulation in stems and its relationship to lodging resistance. Shading by maize significantly reduced cellulose accumulation and the stem breaking strength of the soybean, which were significantly negatively correlated with the lodging rate. In the maize–soybean intercropping system, shading inhibited sucrose transportation and degradation into cellulose in the soybean stem. Less content of cellulose in soybean stem at the seedling stage resulted in lodging in the intercropping system. Compared with shade susceptible varieties, Nandou 12 had higher cellulose accumulation and related enzyme activities in the stem, and thus the stem breaking strength and lodging resistance of the basal stem increased. The higher activities of sucrose phosphate synthase and sucrose synthetase in the stem were associated with shade tolerance and lodging resistance. Thus, we concluded that the high physical strength and high cellulose contents of the stem of shade tolerant soybean reduced the rate of lodging in the maize–soybean intercropping system.

Effect of Waterlogging on Carbohydrate Metabolism and the Quality of Fiber in Cotton (Gossypium hirsutum L.).

Transient waterlogging occurs frequently in the Yangtze River and adversely affects cotton fiber quality. However, the carbohydrate metabolic mechanism that affects fiber quality after waterlogging remains undescribed. Here, the effects of five waterlogging levels (0, 3, 6, 9, and 12 days) were assessed during flowering and boll formation to characterize the carbohydrates, enzymes and genes that affect the fiber quality of cotton after waterlogging. The cellulose and sucrose contents of cotton fibers were significantly decreased after waterlogging for 6 (WL6), 9 (WL9), and 12 d (WL12), although these properties were unaffected after 3 (WL3) and 6 days at the fruiting branch 14–15 (FB14–15). Sucrose phosphate synthase (SPS) was the most sensitive to waterlogging among the enzymes tested. SPS activity was decreased by waterlogging at FB6–7, whereas it was significantly enhanced under WL3–6 at FB10–15. Waterlogging down-regulated the expression of fiber invertase at 10 days post anthesis (DPA), whereas that of expansin, β-1,4-glucanase and endoxyloglucan transferase (XET) was up-regulated with increasing waterlogging time. Increased mRNA levels and activities of fiber SuSy at each fruiting branch indicated that SuSy was the main enzyme responsible for sucrose degradation because it was markedly induced by waterlogging and was active even when waterlogging was discontinued. We therefore concluded that the reduction in fiber sucrose and down-regulation of invertase at 10 DPA led to a markedly shorter fiber length under conditions WL6–12. Significantly decreased fiber strength at FB6–11 for WL6–12 was the result of the inhibition of cellulose synthesis and the up-regulation of expansin, β-1,4-glucanase and XET, whereas fiber strength increased under WL3–6 at FB14–15 due to the increased cellulose content of the fibers. Most of the indictors tested revealed that WL6 resulted in the best compensatory performance, whereas exposure to waterlogged conditions for more than 6 days led to an irreversible limitation in fiber development.

Recovery of photosynthesis, sucrose metabolism, and proteolytic enzymes in Kandelia obovata from rare cold events in the northernmost mangrove, China

Understanding how mangroves respond to rare cold events has implications for both restoration and conservation under climate change scenarios. This study investigated the responses of photosynthesis and activities of key enzymes involving carbon and nitrogen metabolism at different ages of Kandelia obovata to a rare cold event in the winter of 2010. This study took place on Ximen Island, Zhejiang Province, China. We measured the physiological recovery of 2–3-, 5–6-, 9–10- and 54–55-year-old K. obovata trees after freezing injury in February and March in 2011 and 2012, respectively. Chilling injury index and electrolyte leakage of K. obovata increased with increasing tree age in the winter of 2010, and electrolyte leakage in K. obovata at different ages in the winter of 2010 was far higher than that in the winter of 2011. The rare cold events significantly changed the recoveries of the leaf net photosynthetic rate (Pn) and stomatal conductance (Gs); ratios of chlorophyll a/chlorophyll b (Chl a/Chl b); contents of total soluble sugar (TSS), sucrose, free amino acid (FAA), and soluble protein; and activities of sucrose phosphate synthase (SPS), endopeptidase, and carboxypeptidase in K. obovata at different ages. These effects were mainly due to changes in the physiological mechanism in the 2-year-old trees. A clear decrease in Pn of the 2-year-old trees was observed in February 2011, as exemplified by reductions in ratios of Chl a/Chl b and chlorophyll/carotenoid (Chl/Car), as well as inhibition of the levels of TSS and FAA (osmotic substances). During recovery in 2011 and 2012, the activities of SPS and sucrose synthase (SS) were responsible for sucrose synthesis after the rare cold events in 2011, but only SPS activity was one of the main factors contributing to the metabolism of stachyose to sucrose without cold damage in 2012. Carboxypeptidase played a more important role than endopeptidase during protein hydrolysis after the rare cold events. The results suggest that the recovery of photosynthetic capacity in K. obovata was changed after a rare cold event, which is associated with pigment components and activities of SS, SPS, and carboxypeptidase, especially the seedlings.

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.

Cell Wall Invertase and Sucrose Synthase Regulate Sugar Metabolism During Seed Development in Isabgol (Plantago ovata Forsk.)

Isabgol is a commercially cultivated medicinal crop valued for its mucilaginous husk. Changes in sugar metabolism were studied in the developing seeds of Isabgol. Seed samples were collected after 7, 14, 21 and 28 days after anthesis (DAA). Results showed that the post anthesis reduction in soluble sugar content was 67 and 82.8 % in the seed and seed coat respectively. Starch and cellulose increased significantly in the seed after anthesis. Cell wall invertase activity increased after anthesis by 35.2 % and was the highest at 21 DAA. Acid invertase activity did not change significantly during seed development. Sucrose synthase (SuSy) activity increased from 0.12 to 0.34 µmol min−1 mg protein−1 till 28 DAA. Sucrose phosphate synthase (SPS) activity was the highest at 21 DAA (3.81 µmol min−1 mg protein−1). ADP glucose pyrophosphorylase (ADPGlc-PPase) activity also increased post anthesis and increase was four times till 21 DAA and enzyme activity was 12.78 µmol min−1 mg protein−1 at 21 DAA. Present study revealed that cell wall invertase and SuSy are the main enzymes involved in sugar breakdown during seed development in isabgol, while SPS and ADPGlc-PPase were important during storage phase.

Plant density influences fiber sucrose metabolism in relation to cotton fiber quality

Planting density plays an important role in improving cotton yield and regulating fiber quality. A 2-year experiment was conducted to investigate the effects of plant density on sucrose metabolism in relation to fiber quality of field-grown cotton. The results showed that lint yield increased with increasing plant density, fiber micronaire, fiber maturity ratio, and fiber fineness decreased with the increasing of plant density, whereas fiber length, fiber uniformity index, fiber strength, and fiber elongation were little affected by plant density. Increased plant density decreased sucrose synthase (SuSy) activity, sucrose content, and cellulose content in cotton fiber, but increased invertase activity. Increased invertase activity would restrain SuSy activity in cotton fiber: therefore, SuSy activity was the most severely affected enzyme in fiber sucrose metabolism by cotton plant density during fiber development. Abundant sucrose content in fiber after 24 days post anthesis (DPA) and high activities of SuSy and sucrose phosphate synthase (SPS) at 38 DPA were beneficial for cellulose synthesis, and were propitious to optimize the fiber maturity properties. The results also showed that fiber micronaire, maturity ratio, and fineness decreased 0.11, 0.02, and 5.89 mtex, respectively, with each increase of 10,000 plants per hectare. It was concluded that high plant density decreased SuSy activity, sucrose content, and cellulose content, but increased invertase activity in sucrose metabolism, resulting in low fiber micronaire, fiber maturity ratio, and fiber fineness.