Sucrose Synthetase Research Articles

Green and Fast Synthesis of NiCo-MOF for Simultaneous Purification-Immobilization of Bienzyme to Catalyze the Synthesis of Ginsenoside Rh2.

Traditional metal-organic frameworks (MOFs) preparation is generally time-consuming, polluting, and lacking specificity for enzyme immobilization. This paper introduced a facile, rapid, and green method to produce three MOFs subsequently employed to purify and coimmobilize recombinant glycosyltransferase (UGT) and recombinant sucrose synthetase (SUSy) using histidine tag (His-tag) for the specific adsorption of Ni2+ and Co2+ from MOFs. This method simplified enzyme purification from crude extracts and enabled enzymes to be reused. The results demonstrated that NiCo-MOF exhibited a higher enzyme load (115.9 mg/g) than monometallic MOFs. Additionally, the NiCo-MOF@UGT&SUSy demonstrated excellent stability and efficiently produced the rare ginsenoside Rh2 by catalyzing a coupling reaction (95.6 μg/mL), solving the problem of the substrate cost of uridine diphosphate glucose (UDPG). The NiCo-MOF@UGT&SUSy retained 68.97% of the initial activity after 10 cycles. Finally, molecular docking studies elucidated the conversion mechanism of the target product Rh2. This technique is important in the industrialization of ginsenoside production and enzyme purification.

Overexpression of VaSS4 negatively regulates cold tolerance by disturbing ROS balance and decreasing soluble sugar content

Cold stress is one of the major limiting factors for grapevine growth and yield. Sucrose synthetase (SS) is a glycosyl transferase enzyme involved in plant sugar metabolism, which is essential for plant growth and development and response to abiotic stress. However, the function of SS genes in grape cold resistance has not been systematically understood. In the present study, a SS gene from Vitis amurensis named VaSS4 was identified, which was significantly suppressed in response to cold stress. The physicochemical properties, evolutionary relationships, synteny, and selection pressure of VaSS4 were analyzed. Furthermore, VaSS4-overexpressed Arabidopsis and grape calli were obtained to characterize their tolerance to cold stress. Amino acid sequence analysis demonstrated that VaSS4 protein encoded 806 amino acids and contained conserved sucrose synthase domain and glycosyl transferase domain. Overexpression of VaSS4 decreased SS decomposition activity and soluble sugar accumulation under cold stress. Meanwhile, VaSS4 overexpression decreased the reactive oxygen scavenging ability and cold tolerance of Arabidopsis and grape calli. Importantly, overexpression of VaSS4 negatively regulated the expression of cold-related genes in the CBF-dependent pathway compared with WT plants. Overall, these findings not only provide extensive systematic information for Vitis amurensis VaSS4 gene research, but also provide valuable germplasm resources for grape cold resistance breeding.

Cryoprotectant-Mediated Cold Stress Mitigation in Litchi Flower Development: Transcriptomic and Metabolomic Perspectives.

Temperature is vital in plant growth and agricultural fruit production. Litchi chinensis Sonn, commonly known as litchi, is appreciated for its delicious fruit and fragrant blossoms and is susceptible to stress when exposed to low temperatures. This study investigates the effect of two cryoprotectants that counteract cold stress during litchi flowering, identifies the genes that generate the cold resistance induced by the treatments, and hypothesizes the roles of these genes in cold resistance. Whole plants were treated with Bihu and Liangli cryoprotectant solutions to protect inflorescences below 10 °C. The soluble protein, sugar, fructose, sucrose, glucose, and proline contents were measured during inflorescence. Sucrose synthetase, sucrose phosphate synthetase, antioxidant enzymes (SOD, POD, CAT), and MDA were also monitored throughout the flowering stage. Differentially expressed genes (DEGs), gene ontology, and associated KEGG pathways in the transcriptomics study were investigated. There were 1243 DEGs expressed after Bihu treatment and 1340 in the control samples. Signal transduction pathways were associated with 39 genes in the control group and 43 genes in the Bihu treatment group. The discovery of these genes may contribute to further research on cold resistance mechanisms in litchi. The Bihu treatment was related to 422 low-temperature-sensitive differentially accumulated metabolites (DAMs), as opposed to 408 DAMs in the control, mostly associated with lipid metabolism, organic oxidants, and alcohols. Among them, the most significant differentially accumulated metabolites were involved in pathways such as β-alanine metabolism, polycyclic aromatic hydrocarbon biosynthesis, linoleic acid metabolism, and histidine metabolism. These results showed that Bihu treatment could potentially promote these favorable traits and increase fruit productivity compared to the Liangli and control treatments. More genomic research into cold stress is needed to support the findings of this study.

Co-occurring elevated temperature and drought stress inhibit cotton pollen fertility by disturbing anther carbohydrate and energy metabolism

The effects of individually applied heat or drought stress on cotton’s pollen fertility, and consequently on yield formation, have been extensively studied. In contrast, the effects of their compound stress have received minimal attention. To address this, a pond experiment was conducted using a cotton cultivar, Yuzaomian 9110 and the treatments consisted of control (CK), drought stress (DS), elevated temperature (ET), and the combination of elevated temperature and drought stress (ET+DS). Results revealed that ET+DS resulted in larger decreases in cottonseed number per boll and boll weight than DS or ET, which were attributed to the lower pollen fertility under the combined stress compared to either single stress. The decreases in pollen fertility under all stress conditions were further associated with disturbances in anther carbohydrate and energy metabolism. Pollen viability was negatively correlated with sucrose content, but was positively correlated with starch and ATP contents under different conditions. Specifically, DS increased anther sucrose content by increasing sucrose phosphate synthetase (SPS) activity to enhance sucrose synthesis, and by decreasing sucrose synthetase (SuSy) and acid/alkaline INV activities to restrict sucrose hydrolysis to fructose and glucose. Similar to DS, ET+DS increased anther sucrose content, which was attributed to the restricted sucrose hydrolysis, due to the reduced activities of SuSy and acid/alkaline INV, and acid INV activity even was lower under ET+DS than DS. However, ET enhanced acid invertase (INV) activity to promote sucrose hydrolysis, and down-regulated the expression of GhSUT3A/D (sucrose transporter gene), GhSUT4 (sucrose transporter gene) and GhSWEET55 (encoding Sugars Will Eventually Be Exported Transporters proteins) to inhibit sucrose transport into anthers, so the anther sucrose content was decreased. Furthermore, ET, DS and ET+DS treatments significantly decreased starch synthesis by down-regulating the expression of GhAGP, GhGBSS and GhSSS; however, the ET+DS treatment had a lower GhSSS expression than any single stress, which further inhibited amylopectin synthesis and resulted in lower anther starch content compared to CK and either of the individual stresses. In addition, significant reductions were observed in anther pyruvate content under all stress conditions, which inhibited the ATP production in the tricarboxylic acid cycle. Nevertheless, different pathways were involved in the response of energy metabolism to single and combined stresses. In particular, single ET or DS down-regulated GhHK1 and GhPK to decrease pyruvate formation, while the downregulation of GhHK1 and GhPGK were responsible for the decreased pyruvate content under combined stress. Additionally, either single stress resulted in the upregulation and downregulation of GhATP α subunit and GhATP β subunit of ATP synthase, respectively, the opposite was observed under the condition of combined stress, indicating that differential response mechanisms of ATP synthase are activated between the combined stress and any individual stresses. All these confirmed that elevated temperature combined with drought stress have a unique effect on carbohydrate and energy metabolism of anthers, resulting in larger decreases in pollen fertility, cottonseed number per boll and boll weight than either of the stresses alone.

Sugar metabolism and 14-3-3 protein genes expression induced by arbuscular mycorrhizal fungi and phosphorus addition to response drought stress in Populus cathayana

Sugar, as a nutrient exchange substance between arbuscular mycorrhizal (AM) fungi and host plants, plays an important role in the abiotic stress response of mycorrhizal plants. This experiment aimed to study the effects of AM fungi and phosphorus (P) addition on the sugar metabolism and 14-3-3 gene expression of Populus cathayana under drought stress. The results showed that drought affects the process of sugar metabolism by increasing the activities of amylase and invertase, resulting in the decrease of starch content in leaves and roots and the accumulation of soluble sugars (including reducing sugar and sucrose) in roots. Under drought stress, the activity or content of sucrose synthetase, sucrose phosphate synthase, acid invertase, alkaline invertase, reducing sugar, soluble sugar, sucrose, and starch in the root showed the best mycorrhizal effect at the 100 mg P level. The expression levels of the 14-3-3 genes (PcGRF10 and PcGRF11) were significantly increased by mycorrhizal induction under drought stress. These levels were positively correlated with SS, SPS, sucrose, and starch phosphorylase in leaves, as well as with almost all sugar metabolism indicators in roots. However, they were negatively correlated with starch content in both leaves and roots. Sugar metabolism and 14-3-3 protein gene expression were induced by AM fungi and P addition in response to drought stress. The 14-3-3 genes induced by AM fungi may be involved in participating in osmotic regulation during drought stress. This study provides a new idea for the mechanism of sugar metabolism of mycorrhizal plants in arid regions.

Diurnal Regulation of Leaf Photosynthesis Is Related to Leaf-Age-Dependent Changes in Assimilate Accumulation in Camellia oleifera.

In order to clarify the mechanism of diurnal changes in photosynthesis of leaves of different leaf ages in Camellia oleifera, current-year leaves (CLs) and annual leaves (ALs) were used as the test materials to analyze the diurnal changes in photosynthetic parameters, assimilate contents and enzyme activities, as well as structural differences and expression levels of sugar transport regulating genes. The rate of net photosynthesis in CLs and ALs was highest in the morning. During the day, there was a decrease in the CO2 assimilation rate, and this decrease was greater in ALs than in CLs at midday. The maximal efficiency of photosystem II (PSII) photochemistry (Fv/Fm) showed a decreasing trend as the sunlight intensity increased, but no significant difference between CLs and ALs was found. Compared with CLs, ALs showed a greater decrease in the carbon export rate at midday and the levels of sugars and starch increased significantly in ALs, accompanied by higher enzyme activity of sucrose synthetase and ADP-glucose pyrophosphorylase. In addition, compared with CLs, ALs had a larger leaf vein area and higher leaf vein density, as well as higher expression levels of sugar transport regulating genes during the day. It is concluded that the excessive accumulation of assimilate is an important factor contributing to the midday depression of photosynthesis in Camellia oleifera annual leaves on a sunny day. Sugar transporters may play an important regulatory role in excessive accumulation of assimilate in leaves.

VaSUS2 confers cold tolerance in transgenic tomato and Arabidopsis by regulation of sucrose metabolism and ROS homeostasis.

VaSUS2 enhances cold tolerance of transgenic tomato and Arabidopsis by regulating sucrose metabolism and improving antioxidant enzymes activity. Sucrose synthetase (SUS) is a key enzyme of sugar metabolism, and plays an important role in response to abiotic stress in plant. However, the function of VaSUS2 remains unknown in cold tolerance. Here, the cloning and functional characterization of the plasma membrane-localized VaSUS2 gene isolated from Vitis amurensis was studied. The transcript level of VaSUS2 was up-regulated under cold stress in Vitis amurensis. Heterologous expression of VaSUS2 in tomato increased SUS activity, which promoted the accumulation of glucose and fructose under cold treatment. The transgenic tomato and Arabidopsis exhibited higher levels of antioxidant enzymes activity, lower relative electrolyte leakage (REL), malondialdehyde (MDA) and hydrogen peroxide (H2O2) content compared to wild type under cold stress. Importantly, the ability of scavenging reactive oxygen species (ROS) in transgenic plants was significantly improved. Moreover, yeast two-hybrid (Y2H) indicated that VaSnRK1 might be a potential interaction protein of VaSUS2. qRT-PCR showed that sucrose metabolism-related genes SlSUS, SlSPS and SlINV were significantly up-regulated in transgenic tomatoes. Meanwhile, the expression levels of antioxidant enzyme genes and cold-related genes CBF1, COR47 and ICE1 were up-regulated in transgenic plants. Taken together, these results suggested that VaSUS2 was involved in cold tolerance by increasing the levels of soluble sugars, improving the activity of antioxidant enzymes, and up-regulating the expression of cold-related genes in transgenic tomatoes and Arabidopsis.

Preharvest Reduction in Nutrient Solution Supply of Pepper (Capsicum annuum L.) Contributes to Improve Fruit Quality and Fertilizer Efficiency While Stabilising Yields

Optimising fertilisation is an important part of maximising vegetable yield and quality whilst minimising environmental hazards. An accurate and efficient scheme of irrigation and fertiliser based on plants’ nutrient requirements at different growth stages is essential for the effective intensive production of greenhouse pepper (Capsicum annuum L.). In this study, the effects of reducing fertilisation rate by 20%, 40%, 60% and 80% from the day 6 to day 0 before harvest for each layer of peppers on growth, yield, quality and nutrient utilisation were evaluated. The results showed that the morphological indicators (plant height and stem diameter) and biomass of plants decreased gradually with the increase in fertiliser reduction rate. Compared with control (CK) plants, the 20–40% reduction in fertiliser application rate did not cause a significant decrease in biomass and stem diameter but significantly increased the accumulation of N (13.52–15.73%), P (23.09% in 20% reducted-treatment) and K (13.22–14.21%) elements in plants. The 20–80% reduction in fertiliser application before harvest had no significant effects on the nutrient agronomic efficiency of N, P and K elements. However, it decreased the physiological nutrient efficiency and significantly improved the nutrient harvest index of N, P and K. Appropriate reduction in fertiliser application significantly increased the nutrient recovery efficiency (20–40% reduction) and nutrient partial-factor productivity (40% reduction) of N (3.35–6.00% and 12.87%), P (2.47–2.92% and 14.01%) and K (7.49–15.68% and 14.01%), respectively. Furthermore, reducing the fertilisation rate by 20–40% before each harvest had a certain positive effect on the C and N metabolism of pepper leaves and fruits. In particular, the activities of N metabolism-related enzymes (nitrate reductase, nitrite reductase, glutamine synthase, glutamate synthase and glutamate dehydrogenase) and C metabolism-related enzymes (sucrose phosphate synthase, sucrose synthetase, acid invertase and neutral invertase) in leaves and fruits did not significantly different or significantly increased compared with those in CK plants. The results of the representative aromatic substance contents in the fruit screened by the random forest model showed that compared with the CK plants, reducing the fertiliser application by 20–40% before harvest significantly increased the content of capsaicin and main flavour substances in the fruit on the basis of stable yield. In summary, in the process of pepper substrate cultivation, reducing the application of nutrients by 40% from the day 6 to day 0 before each harvest could result in stable yield and quality improvement of the pepper. These results have important implications for institutional precision fertilisation programs and the improvement of the agroecological environment.

English

Two low-light sensitive varieties of sweet corn (Zea mays L.), cultivars Xiantian 5, and Huazhen, were subjected to different shading-intensity treatments during the grain-filling stage in a field experiment in order to clarify physiological mechanisms of lowlight effects on the yield, quality, and sucrose-metabolizing enzyme activity of sweet corn. The results showed that under weak light stress (50% light transmittance), the ear length and diameter, fresh ear yield, grains per row and grain weight, weight per ear and sugar content of the grains decreased sharply, while the bald length and water content of the fresh grains increased significantly. The 50% shading decreased the fresh ear yield, max weight per 100 fresh grains, and soluble sugar content of Xiantian 5 by 40.5, 31.3, and 19.5%, respectively, whereas those of Huazhen were decreased by 17.5, 19.8 and 10.1%, respectively. Shading furthermore suppressed the activities of sucrose phosphate synthase (SPS) and sucrose synthetase (SS), and delayed the emergence of peak SPS activity. Key words: Sweet corn, shading condition, yield, quality, sucrose-metabolizing enzyme.

Temperature-phase transcriptomics reveals that hormones and sugars in the phloem of grape participate in tolerance during cold acclimation.

Most of the upregulated genes contributed to the accumulation of soluble sugars and ABA in the phloem of 'Vitis amurensis' compared to 'Merlot' during cold acclimation. Extreme cold is one of the dominant abiotic factors affecting grape yield and quality. However, the changes in sugars, phytohormones, and gene expression in the branch phloem of different tolerant grape varieties during cold acclimation remain elusive. The data supported that with decreasing temperature, the contents of fructose, sucrose, and ABA in the phloem of Vitis amurensis (cold-tolerant, T) and 'Merlot' (cold-sensitive, S) increased during cold acclimation, and these indicators were higher in T than in S. Furthermore, the activities of sucrose synthetase, sucrose phosphate synthetase, and acid invertase peaked in the early phase of cold acclimation (approximately 5°C) compared to other phases (approximately 28°C, 0°C, - 5°C and - 10°C). Moreover, the RNA sequencing results helped identify a total of 11,343 differentially expressed genes in the phloem of T and S, among which 4912 were upregulated and 6431 were downregulated. In the abscisic acid pathway, CRTISO, PSPY1-1, CYCP707A4-2, PYL4-1, PYL4-2, P2C08, SAPK2, TARAB1, and DBF3 were more highly expressed in T than in S. In the starch and sucrose metabolism pathway, HXK1, PGMP, GLGL1, SUS6, VCINV, BGL11, SSY1, GPS, BAM1 and BAM3 were also more highly expressed in T than in S. Moreover, the genes related to oxidative phosphorylation, such as NDHF, ND4, ND1, NAD7, NAD2, ATPB, YMF19, ATP9, PMA1 and AHA8, were upregulated in T. These results will be beneficial for understanding the potential differences in tolerance across two different cold-tolerant grapes with respect to sugar metabolism and gene expression.

Physiological and transcriptome analysis reveals the differences in nitrate content between lamina and midrib of flue-cured tobacco

Nitrate is an important precursor of tobacco-specific nitrosamines (TSNAs) and a remarkable difference in nitrate accumulation between lamina and midrib of flue-cured tobacco has long been observed. However, the physiological and molecular mechanisms underpinning this difference remain poorly understood. In this study, physiological and genetic factors impacting nitrate accumulation were identified in pot experiments using flue-cured tobacco K326 with contrasting nitrate content between lamina and midrib. The results showed that three times higher NO3-N content was observed in midrib than that in the lamina, along with lower pigment, NH4-N content, nitrate reductase activity (NRA), sucrose synthetase activity (SSA), and glutamine synthetase activity (GSA) in midrib. Transcriptome analysis revealed that expression of genes involved in porphyrin and chlorophyll metabolism, carotenoid biosynthesis, photosynthesis-antenna proteins, photosynthesis, carbon fixation in photosynthetic organisms, starch and sucrose metabolism, nitrogen metabolism, and biosynthesis of amino acids were significantly lower in midrib than in lamina. qRT-PCR results showed that the expression level of nitrate transporter genes LOC107782967, LOC107806749, LOC107775674, LOC107829632, LOC107799198, LOC107768465 decreased by 2.74, 1.81, 49.5, 3.5, 2.64 and 2.96-folds while LOC107789301 increased by 8.23-folds in midrib but not in lamina. Reduced chlorophyll content might result in low carbohydrate formation which is the source of energy and carbon skeleton supply, then the low capacity of nitrogen reduction, assimilation and transportation, and the poor ability of nitrate reallocation but the high capacity of accumulation might lead to nitrate accumulation in midrib. The results laid the foundation for reducing nitrate content and TSNA formation in tobacco midribs and their products.

Key enzymes of sucrose metabolism play an important role in source–sink regulation of walnut fruit growth and development

ABSTRACT Carbohydrate content and metabolism-related enzyme activities were analysed in walnut fruits during fruit growth by artificial manipulation of the leaf-to-fruit ratio (LFR) to investigate the relationship between carbohydrate utilisation and LFR. LFR significantly affected glucose and sucrose content, and sucrose synthetase (SS) activity in the pericarp or kernel. When the leaf number was the same, sucrose content and SS activity in the pericarp and kernel decreased with increasing fruit load, while glucose and fructose content and acid invertase (AI) activity in the pericarp increased gradually. When the fruit number was the same, glucose and sucrose content and SS activity in the pericarp and kernel increased gradually as the number of leaves increased, while fructose content and AI and sucrose phosphate synthetase (SPS) activity in the pericarp increased, thereby indicating that enhanced AI activity in the pericarp improved the competitive ability of the sink when LFR was low during the fast fruit-growing period, while, high AI activity rapidly decomposed sucrose into hexose to supply the energy required for cell multiplication and growth during the fruit fast-growing period, when LFR was high. During the oil transformation period, the increase in sucrose content in the pericarp resulted from SS and SPS activities.

Relationships of Light to Enzyme and Sucrose Transformations in Sugarcane Treated with Paraquat

Relationships of Light to Enzyme and Sucrose Transformations in Sugarcane Treated with Paraquat

Physiological and Expressional Regulation on Photosynthesis, Starch and Sucrose Metabolism Response to Waterlogging Stress in Peanut.

Waterlogging has negative effects on crop yield. Physiological and transcriptome data of two peanut cultivars [Zhongkaihua 1 (ZKH 1) and Huayu 39 (HY 39)] were studied under normal water supply and waterlogging stress for 5 or 10 days at the flowering stage. The results showed that the main stem height, the number of lateral branches, lateral branch length, and the stem diameter increased under waterlogging stress, followed by an increase in dry matter accumulation, which was correlated with the increase in the soil and plant analysis development (SPAD) and net photosynthetic rate (Pn) and the upregulation of genes related to porphyrin and chlorophyll metabolism and photosynthesis. However, the imbalance of the source–sink relationship under waterlogging was the main cause of yield loss, and waterlogging caused an increase in the sucrose and soluble sugar contents and a decrease in the starch content; it also decreased the activities of sucrose synthetase (SS) and sucrose phosphate synthetase (SPS), which may be due to the changes in the expression of genes related to starch and sucrose metabolism. However, the imbalance of the source–sink relationship led to the accumulation of photosynthate in the stems and leaves, which resulted in the decrease of the ratio of pod dry weight to total dry weight (PDW/TDW) and yield. Compared with ZKH 1, the PDW of HY 39 decreased more probably because more photosynthate accumulated in the stem and leaves of HY 39 and could not be effectively transported to the pod.

Potassium Fertilization Stimulates Sucrose-to-Starch Conversion and Root Formation in Sweet Potato (Ipomoea batatas (L.) Lam.).

A field experiment was established to study sweet potato growth, starch dynamic accumulation, key enzymes and gene transcription in the sucrose-to-starch conversion and their relationships under six K2O rates using Ningzishu 1 (sensitive to low-K) and Xushu 32 (tolerant to low-K). The results indicated that K application significantly improved the biomass accumulation of plant and storage root, although treatments at high levels of K, i.e., 300–375 kg K2O ha−1, significantly decreased plant biomass and storage root yield. Compared with the no-K treatment, K application enhanced the biomass accumulation of plant and storage root by 3–47% and 13–45%, respectively, through promoting the biomass accumulation rate. Additionally, K application also enhanced the photosynthetic capacity of sweet potato. In this study, low stomatal conductance and net photosynthetic rate (Pn) accompanied with decreased intercellular CO2 concentration were observed in the no-K treatment at 35 DAT, indicating that Pn was reduced mainly due to stomatal limitation; at 55 DAT, reduced Pn in the no-K treatment was caused by non-stomatal factors. Compared with the no-K treatment, the content of sucrose, amylose and amylopectin decreased by 9–34%, 9–23% and 6–19%, respectively, but starch accumulation increased by 11–21% under K supply. The activities of sucrose synthetase (SuSy), adenosine-diphosphate-glucose pyrophosphorylase (AGPase), starch synthase (SSS) and the transcription of Susy, AGP, SSS34 and SSS67 were enhanced by K application and had positive relationships with starch accumulation. Therefore, K application promoted starch accumulation and storage root yield through regulating the activities and genes transcription of SuSy, AGPase and SSS in the sucrose-to-starch conversion.

Silicon alleviates salinity stress in licorice (Glycyrrhiza uralensis) by regulating carbon and nitrogen metabolism

Salt stress is one of the key factors that limits the cultivation of Glycyrrhiza uralensis Fisch. (G. uralensis) in the northern part of China. In this study, three salt treatments (including 21, 42 and 63 ds/m NaCl/kg dry soil) and four Si (silicon) concentrations (including 0, 1.4, 2.8 and 4.2 ds/m SiO2/kg K2SiO3 in dry soil) were tested using G. uralensis as the plant material in a pot experiment with three replications. The results showed that the application of various concentrations of Si increased sucrose synthetase (SS), sucrose phosphate synthetase (SPS) and glutamine synthetase (GS), as well as nitrate reductase (NR) activities, and promoted carbon and nitrogen metabolism. Si application also increased the root dry weight of G. uralensis. Multilevel comparative analysis showed that the application of 2.8 ds/m SiO2 was the optimum rate for improved growth and yield of G. uralensis under different salt levels. This study provides important information that can form the basis for the cultivation of high-yielding and high-quality G. uralensis in saline soils.

The Influence of Endogenous Sugar on Potato Tuberization in In Vivo Conditions

Sugar (S) and nitrogen (N) play critical roles in potato tuberization and development, which determines the number, size, and yield of tubers. However, the dynamic models of endogenous sugar and nitrogen during tuberization and development are poorly understood. A pot experiment was performed with the potato cultivar Jizhangshu 12. Tuber and leaf samples were continuously taken to detect the morphological changes in stolon or tuber during tuberization and development. Sugar, starch, nitrogen content, and sucrose metabolism-related enzyme activity were measured. Results showed that the starch, fructose, and sucrose content and S/N ratio in leaves decreased significantly, while significant increases were observed in the activities of alkaline invertase (ALI), sucrose synthetase (SS), and sucrose phosphate synthase (SPS), and the ratios of glucose/sucrose and glucose/fructose from stolon hook initiation to subapical swelling. In contrast, nitrogen content and S/N ratio decreased significantly and starch and glucose content, AI (acid invertase), ALI, SS, and SPS activities, and glucose/sucrose ratio in stolons increased significantly. When the diameter from the stolon subapical swelling to the tuber reached 3.0 cm, starch content and glucose/sucrose and glucose/fructose ratios in leaves and tubers, and contents of fructose and sucrose and the activities of AI and SPS in tubers fluctuated; the S/N ratio in both leaves and tubers increased significantly; the activity of SPS in leaves, and activities of ALI and SS in tubers declined significantly. When the tuber diameter increased from 3.0 to 6.0 cm, the content of starch, sucrose, fructose, and total nitrogen, the activities of AI, ALI, and SPS, and the S/N ratio in leaves increased, while the ratios of glucose/sucrose and glucose/fructose showed an opposite trend; the changes in tubers were slight. We conclude that the content of sugar and total nitrogen and the balance of sugar and nitrogen in leaves and stolons changed significantly at tuberization and gradually thereafter. The significant increases in the ratios of glucose/fructose and glucose/sucrose in leaves could be used as indirect indicators to determine tuberization. The ratio of S/N could replace that of nonstructural carbohydrate/nitrogen to characterize potato tuberization and development.

Split application enhances sweetpotato starch production by regulating the conversion of sucrose to starch under reduced nitrogen supply

Split application could improve nitrogen (N) uptake and increase sweetpotato yields under reduced N supply; however, little is known about how it affects the process of starch production in storage roots. An experiment was conducted to determine the effects of three N management strategies [conventional basal N management; 80% of the conventional N rate applied as a basal fertilizer; 80% of the conventional N rate equally split at transplanting and 35 days after transplanting] on starch accumulation, enzyme activity and genes expression in the conversion of sucrose to starch and the relationships among them. The results showed that, compared with conventional basal N management, split application decreased sucrose accumulation by 11.78%, but increased starch accumulation by 11.12% through improving the starch accumulation rate under reduced N supply. The ratio of sucrose synthetase to sucrose phosphate synthase, the enzymatic activity of ADP-glucose pyrophosphorylase (AGPP), starch synthase, and the expression of their corresponding genes were promoted by split application under reduced N supply and were positively correlated with starch accumulation rate. AGPP is the rate-limiting enzyme in starch synthesis in storage roots under different N management strategies. These results indicate that starch accumulation was enhanced by split application through regulating the activity and gene expression of key enzymes involved in the conversion of sucrose to starch under reduced N supply.

Photosynthetic Regulation Under Salt Stress and Salt-Tolerance Mechanism of Sweet Sorghum.

Sweet sorghum is a C4 crop with the characteristic of fast-growth and high-yields. It is a good source for food, feed, fiber, and fuel. On saline land, sweet sorghum can not only survive, but increase its sugar content. Therefore, it is regarded as a potential source for identifying salt-related genes. Here, we review the physiological and biochemical responses of sweet sorghum to salt stress, such as photosynthesis, sucrose synthesis, hormonal regulation, and ion homeostasis, as well as their potential salt-resistance mechanisms. The major advantages of salt-tolerant sweet sorghum include: 1) improving the Na+ exclusion ability to maintain ion homeostasis in roots under salt-stress conditions, which ensures a relatively low Na+ concentration in shoots; 2) maintaining a high sugar content in shoots under salt-stress conditions, by protecting the structures of photosystems, enhancing photosynthetic performance and sucrose synthetase activity, as well as inhibiting sucrose degradation. To study the regulatory mechanism of such genes will provide opportunities for increasing the salt tolerance of sweet sorghum by breeding and genetic engineering.

Arbuscular mycorrhizal fungi alter carbohydrate distribution and amino acid accumulation in Medicago truncatula under lead stress

This study aims to understand the effect of arbuscular mycorrhizal (AM) inoculation on the regulation of carbon and nitrogen metabolites in Medicago truncatula plants under lead (Pb) stress. Root morphology, nutrient, photosynthesis, sucrose cleaving enzymes, the transcription levels of sucrose transporters, and metabolite profiling were evaluated via a two-factor (AM inoculation and Pb stress) pot experiment. AM inoculation alleviated the damage caused by Pb to photosynthesis and increased phosphorus uptake. AM inoculation decreased the shoot sucrose content but increased root sucrose content. The transcription of MtSUT1-1 and MtSUT4-1 in roots was upregulated by AM inoculation, which indicates that AM plant has a higher ability of sucrose transport. Both Pb stress and AM inoculation stimulated the activity of acid invertase and sucrose synthetase in roots. In shoots, minor amino acids such as cysteine were increased by AM inoculation. Sucrose content was negatively related to asparagine content. Therefore, AM inoculation may alleviate Pb toxicity by promoting the transport of sucrose from shoot to root, promoting the cleaving of sucrose in roots, and increasing minor amino acids accumulation.