Sucrose Phosphate Synthase Research Articles

Effects of potassium on fruit soluble sugar and citrate accumulations in Cara Cara navel orange (Citrus sinensis L. Osbeck)

Sugars and organic acid are key factors for sensory properties of fruit quality. Potassium (K) is an essential macroelement and is also known as quality element. This study aims to investigate how K affects quality improvement particularly sucrose, fructose, glucose and citrate accumulations in Cara Cara navel orange. K fertilizer increased fruit sucrose, fructose, glucose and citrate concentrations and the ratios of total soluble sugars and citrate, particularly the ratios increased more in the treatment of 0.50 kg/plant K fertilizer. These results showed that suitable amount of K fertilizer could improve fruit quality of Cara Cara navel orange. Further study showed that, at early stage of fruit development, K fertilizer played more important roles in degrading sucrose due to the increased activities of sucrose-degrading enzymes including invertase and sucrose synthase-cleavage activity. Conversely, at late stage of fruit development, K fertilizer played more important roles in re-synthesizing sucrose due to the higher activities of sucrose-synthesizing enzymes including sucrose synthase-synthetic activity and sucrose phosphate synthase. The above results suggested that the upregulations of sucrose-degrading and sucrose-synthesizing enzyme activities caused by K fertilizer were conducive to improving sucrose metabolism and sink strength, and then increased the concentrations of sucrose, fructose and glucose in fruit. K fertilizer increased the activities of citrate-synthesizing enzymes including citrate synthetase and phosphoenolpyruvate carboxylase, but had no significant impacts on the activities of citrate-degrading enzyme, indicating that K fertilizer increased citrate accumulations at least partially by promoting its synthesis. This study finally suggested that K fertilizer improved the accumulations of soluble sugar and citrate in Cara Cara navel orange.

Isolation and characterization genes in lobi-lobi (Flacourtia inermis) related to sugar metabolism

Lobi-lobi (Flacourtia inermis) is probably a native plant to the Moluccas (Maluku). In Indonesia, lobi-lobi fruit is used for traditional medicine because it has a phenolic compound. Sugar metabolism involved several genes that control the photosynthesis pathway. This research aims to isolate and characterize genes in which related to sugar metabolism in Lobi-lobi. The lobi-lobi contigs have 694 452 contigs produced by the velvet-assembled genome. The sugar-related genes were isolated from the assembled-genomes database against to SwissProt Database using the BLASTX program. The six-sugar related-genes were characterized involved 36 contigs of Sucrose-phosphate synthase (SPS), six contigs of Sucrose-phosphatase (SPP), 46 contigs of Sucrose synthase (SUS), 36 contigs of Alkaline/neutral invertase (INV), four contigs of Cytosolic invertase (CINV), and 17 contigs of Beta-fructofuranosidase (CWINV), respectively. Comprehensive research on sugar metabolism was used in this study. Then, the data also revealed the biological functions of these genes in flowering time control in Lobi-lobi.

Characterization of rambai (Baccaurea motleyana) genes putatively involved in sugar metabolism

Rambai (Baccaurea motleyana) is one of the underutilized fruits native to Indonesia. Rambai has high antioxidant activities containing phenolic, flavonoid, and anthocyanin compounds, secondary metabolite compounds derived from sugar metabolism. The sugar metabolism involved several related genes. This research aimed to characterize genes putatively involved in sugar metabolism in Rambai. Six sugar gene families were identified from 37 077 contigs of the assembled-transcriptome database against to UniProt database using the BLASTX program. The six sugar-related genes were characterized involved nine contigs of sucrose-phosphate synthase (SPS), three contigs of sucrose-phosphatase (SPP), 14 contigs of sucrose synthase (SUS), 19 contigs of alkaline/neutral invertase (INV), one contig of cytosolic invertase (CINV) and five contigs of beta-fructofuranosidase (CWINV). This research aims to give a comprehensive study of the sugar metabolism mechanism in B. motleyana. The data also revealed the genes that encoded the enzymes that were putatively involved in sugar metabolism.

Characterization of genes encoding key enzymes involved in sugar metabolism of matoa (Pometia pinnata)

Matoa (Pometia pinnata JR Forst. & G Forst.) is one of Indonesia’s underutilized fruits, which can grow to giant trees up to 50 m (164 ft) and found naturally in the Asia-Pacific region, mainly in lowland tropical areas about 14°N to 20°S. Matoa fruit contains phytochemical compounds such as flavonoid, tannin, and saponin, secondary metabolite compounds derived from sugar metabolism. Sugar metabolism involved several genes that control the photosynthesis pathway. This research aimed to isolate and characterize the gene related to sugar metabolism depending on the assembled-transcriptome database genome against the UniProt database using the BLASTX program. Six gene sequences characterized 176,002 number of contigs that are nine contigs of Sucrose-phosphate synthase (SPS), four contigs of Sucrose-phosphate (SPP), 12 contigs of Sucrose synthase (SUS), 19 contigs of Alkaline/neutral invertase (INV), four contigs of Cytosolic invertase (CINV), 20 contigs of Beta-fructofuranosidase (CWINV). The research lays the foundation for a comprehensive study of biological mechanisms involved in sugar metabolism growth and the development life circle of matoa.

Role of sucrose phosphate synthase and vacuolar invertase in postharvest sweetening of immature sweetpotato tuberous roots (Ipomoea batatas (L.) Lam cv ‘Xinxiang’)

Postharvest sweetening can improve the eating quality of sweetpotato, particularly of immature sweetpotato. In this study, soluble sugar content, activities of sucrose phosphate synthase (SPS) and vacuolar invertase (VIN) enzymes and expression of three IbSPSs, five IbVINs and two vacuolar invertase inhibitory factor (IbVIFs) genes were examined in immature sweetpotato cv ‘Xinxiang’ during 30 days storage at 20, 13 and 4 °C. Results showed that sucrose content increased at all temperatures, while glucose and fructose mainly increased at 4 °C. However, chilling injury developed at 4 °C and postharvest sweetening at 20 °C is potentially a safer option. The sucrose level was correlated with SPS activity and SPS activity is not manipulated at transcriptional stage. Fructose/glucose content was correlated with VIN activity. Transcript level of IbVIN1 was correlated with VIN activity and sweetness index in sweetpotato roots. Therefore, IbVIN1 could be a candidate gene in cultivating variety high in sweetness.

Comparative expression analysis of microRNAs and their targets in emerging bio-fuel crop sweet sorghum (Sorghum bicolor L.)

Sweet sorghum (Sorghum bicolor L) is a C4 plant, and it recently has emerged as a model feedstock for biofuel production. MicroRNAs (miRNAs) are known as key regulators in different biological processes in plant including sugar accumulation. Despite bioinformatics analyses for the discovery of miRNAs and prediction of targets in recent years, little information is available on the expression of mature candidate miRNAs and biological validation of their targets in sweet sorghum. This study aims to gain an insight on the conserved and novel miRNAs as well as their potential targets associated with biofuel related traits, with the help of next generation RNA sequencing (RNA-seq) followed by RT-qPCR validation. In order to identify biofuel related miRNAs and their potential targets in sweet sorghum, small RNA libraries were constructed from four varieties, i.e., Achi Turi, Dale, Dasht Local, and Topper 76-6 after being grown under controlled conditions, and sequenced by Illumina Hiseq 2000 platform. Sequencing yield from 12 libraries, 3 from each variety i.e., leaf vegetative stage, leaf reproductive stage and stem reproductive stage, ranged from 19 to 48 million reads. Mapping with Sorghum bicolor ensemble genome while aligned with miRBase-release 21, 276 conserved and novel biofuel relevant miRNAs were predicted in all varieties. Target prediction by employing psRNA Target tool indicated 475 biofuel relevant targets for identified conserved and novel miRNAs. We performed the RT-qPCR analysis on selected 36 candidate mature miRNAs along with their 18 targets. Potential biofuel relevant targets identified in our study included the sucrose phosphate synthase (SPS), sucrose synthase (SUS), sucrose transporters (SUT) and invertase (INV) enzymes, which are believed to play key role in sucrose synthesis, accumulation and transport. Altogether, 19 predicted miRNAs and their 15 target mRNAs showed significant change in expression under the three growth stages of four varieties. Significant down-regulation at reproductive stage was observed with Sbi-miR160, Sbi-miR164, Sbi-miR166 and Sbi-miR168 in most of the varieties while significant upregulation was observed for Sbi-miR156a and Sbi-miR156e during vegetative stages. This study showed a positive as well as negative correlations between levels of miRNA expressions and that of their target mRNAs. These findings, both computational and experimental, provide valuable insights on the role of miRNAs and their targets during sugar accumulation stages. The identification of these significantly expressed miRNAs and their targets will help to explore the molecular mechanisms for sugar accumulation in sweet sorghum.

SnRK1 phosphorylation of SDH positively regulates sorbitol metabolism and promotes sugar accumulation in peach fruit.

Fruit quality depends largely on the type and amount of sugar accumulated in the fruit. In peach [Prunus persica (L.) Batsch], sorbitol is the main photosynthetic product and plays a crucial role in sugar metabolism. As a conserved energy sensor, SNF1-related kinase 1 (SnRK1) is involved in the regulation of carbon metabolism. In this study, SnRK1 was able to respond to induction by treatment with exogenous trehalose and sorbitol on ‘Ruipan 17’ peach fruit. After treatment with 100-mM trehalose for 3 h, the SnRK1 activity decreased by 18% and the activities of sorbitol dehydrogenase (SDH) and sucrose synthase (SS) also decreased significantly, but sucrose phosphate synthase (SPS) activity increased significantly; whereas sorbitol treatment under the same conditions resulted in a 12.6% increase in SnRK1 activity and the activities of SDH and SS synthase also increased significantly, compared with the control. The contents of glucose, fructose and sucrose in peach fruit increased significantly after 3 h of sorbitol treatment. In addition, the interactions between PpSnRK1α and enzymes PpSDH and PpSPS were confirmed by yeast two-hybrid method and the phosphorylation of PpSnRK1α and PpSDH was detected in vitro. Taken together, these results suggest that SnRK1 promotes sorbitol metabolism by activating SDH and it also regulates the activities of SS and SPS that enhance sucrose accumulation in peach fruit. SnRK1 protein kinase is involved in sugar metabolism and has the potential to be used for improving fruit quality.

Up-regulated glycolysis, TCA, fermentation and energy metabolism promoted the sugar receding in ‘Shixia’ longan (Dimocarpus longan Lour.) pulp

Sugar receding, a drastic decrease of total soluble solid (TSS) in pulp, leads to decreased sweetness and deterioration of longan fruits during on-tree preservation. Although soluble acid invertases were proved as key factors regulating sugar receding, systematic analysis of the other pathways regulating this process was still lacked. Significant decreased TSS (by 40.61%) and sucrose (by 66.71%) but slight decreased fructose and glucose during 95–127 days after flowering (DAF) indicated a rapid conversion of sucrose to hexose and consumption of hexose in ‘Shixia’ longan pulp. TMT-labeled proteomic analysis of longan pulp at 95, 110 and 127 DAF identified 575 proteins differently expressed (≧1.2-fold or ≦0.833-fold) in at least two stages (BDEPs). GO annotation of the BDEPs showed that the enriched biological processes terms were: response to inorganic substance, cadmium ion, stimulus and chemical, catabolic processes of carbohydrate, glucose, monosaccharide and hexose, and monosaccharide metabolic process. Mapman visualization of the BDEPs indicated that down-regulation of the key proteins involved in starch synthesis & degradation (ie. Starch phosphorylase L & isoamylase), sucrose synthesis (ie. sucrose-phosphate synthase & sucrose-6-phosphatase) and cytoplasmic sucrose degradation (ie. neutral invertase, sucrose synthase) but up-regulation of the enzymes for vacuolar sucrose degradation (soluble acid invertase) and most of the proteins involved in the cytosolic and plastidial glycolysis (Calvin cycle), fermentation, TCA, and energy metabolism promoted the consumption of hexose. Taken together, the up-regulated glycolysis, fermentation, TCA and energy metabolism might promote sucrose decomposition and thus sugar receding of longan pulp.

Mutation of UDP-glucose binding motif residues lead to increased affinity for ADP-glucose in sugarcane sucrose phosphate synthase.

Plant sucrose-phosphate synthase (SPS) contains a glycosyltransferase domain, which specifically catalyzes reactions with the nucleotide sugar uridine diphosphate glucose (UDP-G) as a donor substrate. Unlike plant SPS, bacterial SPS is predicted to bind other nucleotide sugars, such as adenosine diphosphate glucose (ADP-G). This study aimed to identify the UDP-G binding site of sugarcane (Saccharum officinarum) SPS (SoSPS1) and to improve its affinity for ADP-G by site-directed mutagenesis. To achieve targeted mutagenesis, amino acid distribution and comparative modeling studies were performed, followed by site-directed mutagenesis of SoSPS1 in the putative UDP-G binding motif. The N-terminal deletion of SoSPS1 (∆N-SoSPS1) was used for enzymatic analysis. The results showed that mutations in the R-X4-K, E-X7-E, and H-X5-V motifs significantly affect UDP-G and ADP-G binding. Mutations at R496 and K501 severely attenuate the affinity for UDP-G. Additionally, alanine substitutions at E591 and V570 decreased the UDP-G affinity but remarkably increased its ADP-G affinity. The R-X4-K motif plays a crucial role in the UDP-G binding site and catalytic activity of plant SPS; thus, its alteration to other amino acids was not viable. The E-X7-E and H-X5-V motifs may bind to the nucleotide glucose substrate, indicating that these motifs are involved in substrate specificity. These results agree with substrate docking simulations at the mutated residue positions, supporting the experimental results. These results demonstrate that mutation of E591 and V570 severely attenuated the UDP-G affinity, while retaining its activity against ADP-G, offering strategic insights into increasing sucrose synthesis and plant growth.

Sucrose-phosphate phosphatase from sugarcane reveals an ancestral tandem duplication

BackgroundSugarcane is capable to store large amounts of sucrose in the culm at maturity hence it became a major source of sucrose for the food and the renewable energy industries. Sucrose, the main disaccharide produced by photosynthesis, is mainly stored in the vacuole of the cells of non-photosynthetic tissues. Two pathways are known to release free sucrose in plant cells, one is de novo synthesis dependent on sucrose phosphate synthase (SPS) and sucrose phosphate phosphatase (S6PP) while the other is regulatory and dependent on sucrose synthase (SuSy) activity. The molecular understanding of genes that give rise to the expression of the enzyme sucrose phosphate phosphatase, responsible for the release of sucrose in the last synthetic step lag behind the regulatory SuSy gene.ResultsSugarcane genome sequencing effort disclosed the existence of a tandem duplication and the present work further support that both S6PP.1 and S6PP_2D isoforms are actively transcribed in young sugarcane plants but significantly less at maturity. Two commercial hybrids (SP80–3280 and R570) and both Saccharum spontaneum (IN84–58) and S.officinarum (BADILLA) exhibit transcriptional activity at three-month-old plants of the tandem S6PP_2D in leaves, culm, meristem and root system with a cultivar-specific distribution. Moreover, this tandem duplication is shared with other grasses and is ancestral in the group.ConclusionDetection of a new isoform of S6PP resulting from the translation of 14 exon-containing transcript (S6PP_2D) will contribute to the knowledge of sucrose metabolism in plants. In addition, expression varies along plant development and between sugarcane cultivars and parental species.

Transcriptome profiling analysis of two contrasting barley genotypes in general combining ability for yield traits

General combining ability (GCA) has been successfully used to evaluate the parental performance in hybrid breeding program, while the molecular basis of GCA still remains unknown. In this study, RNA-Seq was employed to compare the transcriptome profiles that determined the GCA for yield-related traits in two different barley genotypes. A total of 1051 differentially expressed unigenes (DEGs) including 599 up-regulated DEGs and 452 down-regulated DEGs were found between Baodamai 12 and Ximala 22. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that many DEGs participated in metabolic process, stimulus response, catalytic activity and biosynthesis. Furthermore, 11 DEGs involved in the starch and sucrose metabolism pathway were discovered, among which eight up-regulated genes were related to beta-fructofuranosidase, pectinesterase, beta-glucosidase and hexokinase, while the other three down-regulated genes were related to sucrose-phosphate synthase, beta-glucosidase and hexokinase. These DEGs might contribute to the differences of GCA for grain weight between the two genotypes. The results may provide a new insight in the studying of the molecular basis of GCA and establish a foundation for further genomic research on the improvement of combining ability in barley breeding program.

Regulation of Ultrasonic Treatment on the Activity of Sugar Metabolism Relative Enzyme and Quality of Coconut Water

In this study, tender coconuts were treated with high-intensity ultrasound (US) for 20 min at a frequency of 20 kHz and a power of 2400 W. Compared with control group, US treated coconut water had a higher content of total soluble solid and sugar/acid ratio along with a lower pH value and conductivity, and the content of sucrose, fructose and glucose were also higher. Results from HS-SPME/GC-MS showed that there was no significant difference in the content of volatile compounds in coconut water before and after US treatment. The activities of sugar metabolism enzyme such as sucrose phosphate synthase, sucrose synthase, acid invertase (AI) and neutral invertase were inhibited by US, of which AI had the strongest inactivation. Circular dichroism and fluorescence spectra showed that the secondary and tertiary structure of AI molecules was destroyed with the increase of US intensity and time, which was confirmed by the change of particle size distribution pattern and scanning electron microscopy. Molecular docking and molecular dynamics showed that US treatment prevented the recognition and binding of sucrose and AI molecules, thereby inhibiting the decomposition of sucrose. In conclusion, our results indicate that US can inhibit the activity of AI and maintain the sugar content to increase the quality as well as extend the shelflife of coconut water, which will bring more commercial value.

Changes in sucrose metabolism in maize varieties with different cadmium sensitivities under cadmium stress.

Sucrose metabolism contributes to the growth and development of plants and helps plants cope with abiotic stresses, including stress from Cd. Many of these processes are not well-defined, including the mechanism underlying the response of sucrose metabolism to Cd stress. In this study, we investigated how sucrose metabolism in maize varieties with low (FY9) and high (SY33) sensitivities to Cd changed in response to different levels of Cd (0 (control), 5, 10, and 20 mg L-1 Cd). The results showed that photosynthesis was impaired, and the biomass decreased, in both varieties of maize at different Cd concentrations. Cd inhibited the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) (sucrose synthesis), and stimulated the activities of acid invertase (AI) and SS (sucrose hydrolysis). The total soluble sugar contents were higher in the Cd-treated seedlings than in the control. Also, Cd concentrations in the shoots were higher in SY33 than in FY9, and in the roots were lower in SY33 than in FY9. The decreases in the photosynthetic rate, synthesis of photosynthetic products, enzyme activity in sucrose synthesis direction, and increases in activity in hydrolysis direction were more obvious in SY33 (the sensitive variety) than in FY9 (the tolerant variety), and more photosynthetic products were converted into soluble sugar in SY33 than in FY9 as the Cd stress increased. The transcript levels of the sugar transporter genes also differed between the two varieties at different concentrations of Cd. These results suggest that sucrose metabolism may be a secondary response to Cd additions, and that the Cd-sensitive variety used more carbohydrates to defend against Cd stress rather than to support growth than the Cd-tolerant variety.

Hot air treatment inhibits chilling injury in peaches by regulating metabolism of sugar and organic acid

ABSTRACT Hot air (HA) treatment has been demonstrated to control chilling injury (CI) in peaches effectively, however, little is known about the effects of HA on the changes of sugar and organic acid. In order to explore the relationship among CI susceptibility, soluble sugar and organic acid metabolism, peach fruit (Prunus persica) were treated with HA (40°C, 4 h) and then stored at 1°C for 35 days plus 3 days at 20°C. Results showed that HA avoided or decreased the development of CI symptoms and maintained a better quality of peaches. HA suppressed sucrose degradation by inhibiting expression of invertase as well as enhancing the relative expressions of sucrose synthase and sucrose phosphate synthase. The low degradation of sucrose contributed to low contents of glucose and fructose in the treated groups. Besides, HA significantly increased contents of citric and malic acids during the whole storage by enhancing the expressions of citrate synthase and malate dehydrogenase, but inhibiting malate synthase. These results suggest that HA suppressed chilling injury by regulating sucrose degradation and organic acid metabolism. The high contents of sucrose, citric and malic acids contributed to enhancement of CI tolerance in peaches.

Molecular cloning and expression analysis of sucrose phosphate synthase genes in cassava (Manihot esculenta Crantz)

Sucrose phosphate synthase (SPS), a key rate-limiting enzyme in the sucrose biosynthesis pathway in plants, is encoded by a multi-gene family. Until recently, the identification and characterization of the SPS gene family have been performed for dozens of plant species; however, few studies have involved a comprehensive analysis of the SPS family members in tropical crops, such as cassava (Manihot esculenta Crantz). In the current study, five SPS genes (MeSPS1, MeSPS2, MeSPS3, MeSPS4, and MeSPS5) were isolated from cassava, and their sequence characteristics were comprehensively characterized. These MeSPS genes were found distributed on five chromosomes (Chr2, Chr14, Chr15, Chr16, and Chr18). Phylogenetic analysis showed that the MeSPS protein sequences were clustered into three families, together with other SPS sequences from both dicot and monocot species (families A, B, and C). The spatio-temporal expression pattern analysis of MeSPS genes showed a tissue-specific and partially overlapping expression pattern, with the genes mainly expressed in source tissues during cassava growth and development. Correlation analysis revealed that the expression of MeSPS genes correlated positively with root starch content, indicating that the expression of MeSPS genes might accelerate the rate of starch accumulation in the roots of cassava plants.

Physiological effects of humic acid in peanut growing in continuous cropping soil

AbstractAlthough humic acid has been demonstrated to improve the yield of some crops, the long‐term effects of continuous cropping on peanut (Arachis hypogaea L.) remain largely undetermined. In the present study, we aimed to compare the continuous effects of different concentrations of humic acid on the continuously cropped peanut. A 3‐yr experiment was conducted in the North China Plain. Treatments of 50 kg ha−1 (T1), 100 kg ha−1 (T2), and 150 kg ha−1 (T3) humic acid were applied with inorganic fertilizer along with the equal N, P, and K inputs. Compared with the control group, humic acid increased the yield and oxidative stress tolerance of continuously cropped peanut. To elucidate the mechanism, various physiological indicators were evaluated and compared in this study. First, humic acid increased chlorophyll content and the ability to incorporate nutrients, and the maximum effect was achieved by T3 in 2016. Second, the activities of nitrate reductase and sucrose phosphate synthase in peanut leaves were significantly increased after humic acid treatment, and the most increase was achieved by T2. Third, the activities of antioxidant enzymes were increased, the malondialdehyde (MDA) content was reduced in 2016–2018 by T3, and the same effects were observed in roots and leaves. Fourth, the content of the hormone was changed after humic acid treatment. Collectively, humic acid improved the yield and tolerance of continuously cropped peanut due to the above‐mentioned four reasons, which were conducive to alleviating the obstacles of continuously cropped peanut.

Impaired chloroplast positioning affects photosynthetic capacity and regulation of the central carbohydrate metabolism during cold acclimation

Photosynthesis and carbohydrate metabolism of higher plants need to be tightly regulated to prevent tissue damage during environmental changes. The intracellular position of chloroplasts changes due to a changing light regime. Chloroplast avoidance and accumulation response under high and low light, respectively, are well known phenomena, and deficiency of chloroplast movement has been shown to result in photodamage and reduced biomass accumulation. Yet, effects of chloroplast positioning on underlying metabolic regulation are less well understood. Here, we analysed photosynthesis together with metabolites and enzyme activities of the central carbohydrate metabolism during cold acclimation of the chloroplast unusual positioning 1 (chup1) mutant of Arabidopsis thaliana. We compared cold acclimation under ambient and low light and found that maximum quantum yield of PSII was significantly lower in chup1 than in Col-0 under both conditions. Our findings indicated that net CO2 assimilation in chup1 is rather limited by biochemistry than by photochemistry. Further, cold-induced dynamics of sucrose phosphate synthase differed significantly between both genotypes. Together with a reduced rate of sucrose cycling derived from kinetic model simulations our study provides evidence for a central role of chloroplast positioning for photosynthetic and metabolic acclimation to low temperature.

Non-structural carbohydrates and sugar export in grapevine leaves exposed to different light regimes.

Light is a main environmental factor that determines leaf microclimate within the vine, as well as its photosynthesis and carbohydrate metabolism. This study aimed to examine the relationships between photosynthesis, carbohydrate metabolism, and the expression of related genes in leaves of grapevine grown under different radiation regimes. During the 2014/2015 growing season, an experiment was conducted on a Malbec vineyard (Vitis vinifera L.) in which four radiation exposure treatments were established on the leaves: (1) East, (2) West, (3) Sun, and (4) Shade (i.e., reduction in light intensity). Diurnal dynamics of photosynthesis and non-structural carbohydrates were measured and leaf export rates were calculated. Transcript profiles of leaf sugar transporters (VvHT1, VvHT3, VvSUC27), a sucrose phosphate synthase enzyme (VvSPS), and invertases (VvGIN1, VvCWI) were also examined. We showed that East and Sun leaves had higher daily photosynthetic and export rates than West leaves, which was mainly explained by the environmental conditions (air and leaf temperature, VPDleaf-air ) and leaf water status. Shade leaves accumulated less starch and soluble sugars than exposed leaves, which correlated with a higher expression of hexose transporters and invertases. The hypotheses that these sugars in Shade leaves would play a role as signaling molecules and/or have increased sink strength and phloem unloading are discussed. These results allow us to understand the physiological and molecular behavior of leaves exposed to different radiation regimes, which can be used to design appropriate vineyard management practices.

Nitric Oxide and Its Interaction with Hydrogen Peroxide Enhance Plant Tolerance to Low Temperatures by Improving the Efficiency of the Calvin Cycle and the Ascorbate–Glutathione Cycle in Cucumber Seedlings

The present study was aimed to assess the effect of nitric oxide (NO) and the interaction of NO with hydrogen peroxide (H2O2) on plant tolerance to low temperatures in cucumber seedlings. Exogenous NO significantly increased the endogenous NO content, initial and total activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), RuBisCO carboxylation rate (Vc,max), RuBP regeneration rate (Jmax) and the transcript levels of related genes in cucumber seedlings under low temperatures (11 °C/7 °C); however, the effect of NO was blocked by PTIO (NO scavenger). In addition, the SNP treatment significantly improved the contents of glucose, fructose, sucrose, starch, and the activities of sucrose phosphate synthase (SPS), acid invertase (AI), sucrose synthase (SS), as well as the expression levels of SUCROSE PHOSPHATE SYNTHASE 1&2 (SPS1, SPS2), SUCROSE TRANSPORTER 1&2 (SUT2, SUT4), β-starch hydrolase (BAM), and invertase gene (INVERTASE) in cucumber leaves under low temperatures, and the positive effect of NO was impaired by PTIO. Furthermore, we found that the H2O2, induced by NO, participated in NO-induced elevation of ascorbic acid (AsA), glutathione (GSH), and increased activities of related enzymes in the AsA-GSH cycle at low temperatures. However, the positive effect of NO was blocked by l-NAME (NOS inhibitor), PTIO, DPI (inhibitor of NADPH oxidase), and DMTU (reactive oxygen species scavenger). Taken together, our findings indicate that NO increased the low temperature tolerance of cucumber seedlings via H2O2 by improving the efficiency of the Calvin cycle, which in turn increased the carbohydrates content and accelerated the AsA-GSH cycle to enhance ROS scavenging.

Exogenous supplementation of melatonin alters representative organic acids and enzymes of respiratory cycle as well as sugar metabolism during arsenic stress in two contrasting indica rice cultivars

The objective of the present investigation was to understand the impact of exogenously applied melatonin on mitochondrial respiration and sugar metabolism in two contrasting rice cultivars, viz., Khitish (arsenic-susceptible) and Muktashri (arsenic-tolerant) under arsenic-stress. Melatonin effectively restored the level of organic acids like pyruvic acid, malic acid and more particularly citric acid by 33 % in Khitish which were lowered during arsenic-stress, whereas their levels were further elevated in Muktashri to provide energy for defence against arsenic-induced injury. Arsenic-exposure led to a significant inhibition in enzyme activities as well as corresponding transcript level of key respiratory enzymes, viz., pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, succinate dehydrogenase and malate dehydrogenase, intriguingly more prominently in case of Khitish. Conversely, melatonin supplementation, irrespective of cultivars, considerably improved the activity of the above enzymes and corresponding gene expressions during stress, indicating acceleration in the rate of Krebs cycle. Melatonin supplementation also stimulated the accumulation of total soluble sugars by 62 % and 25 %, reducing sugars by 50 % and 44 % and non-reducing sugars by 75 % and 14 % in Khitish and Muktashri respectively, concomitant with higher activities of acid invertase, sucrose synthase and sucrose phosphate synthase enzymes, along with the expression of corresponding genes. Enhanced starch accumulation via regulation of alpha amylase and starch phosphorylase activities and gene expression, by melatonin also contributed towards better stress tolerance. Overall, this work illustrated the efficacy of melatonin in the regulation of representative organic acids and enzymes of respiratory cycle along with starch and sugar metabolism in rice cultivars under arsenic toxicity.