Sucrose Phosphate Synthase Activity Research Articles

Melatonin application improves berry coloration, sucrose synthesis, and nutrient absorption in ‘Summer Black’ grape

In this study, we investigated the effects of melatonin application on berry coloration, sugar accumulation, and nutrient absorption in ‘Summer Black’ grapes. Melatonin spraying at 100 μmol L−1 on grapes during veraison induced skin coloration earlier than that in controls, as well as higher transcript abundance of anthocyanin biosynthesis-related genes and transcription factors MYBA1 and MYBA2. Melatonin treatment increased the soluble sugar content, especially of sucrose, by promoting the activity of sucrose phosphate synthase, and also increased endogenous melatonin content and the concentrations of mineral nutrients N, K, Cu, Fe, and Zn in grape berries. Correlation analysis suggested that high sugar content promoted anthocyanin synthesis. These findings provide a sound theoretical basis for the development of techniques aimed to achieve optimum coloration of grapes in hot and rainy regions.

Preharvest methyl salicylate treatment enhance the chilling tolerance and improve the postharvest quality of apricot during low temperature storage

Apricot is highly susceptible to chilling injury during low temperature storage, while methyl salicylate (MeSA) can alleviate chilling injury and enhance the postharvest quality of fruit. The apricots were preharvest sprayed twice with 0.05 mmol L−1, 0.1 mmol L−1 and 0.2 mmol L−1 of MeSA solution, and then were harvested and stored at 2 °C (humidity of 70 %). After cold storage for every 4 d, apricots were transferred to 20 °C for 2 d to determine the fruit quality. Our results indicated that 0.2 mmol L−1 MeSA treatment exhibited the best efficacy. Preharvest MeSA treatment could reduce decay rate and chilling injury (CI) index, and maintain firmness, soluble solid content (SSC), organic acids and antioxidant capacities at a relative higher level. Preharvest MeSA treatment inhibited the increase of electrolyte leakage, malondialdehyde (MDA) and H2O2 content in apricot. The chilling temperature of 2 °C could lead to the degradation of sucrose to fructose and glucose in apricot. At the same time, preharvest MeSA treatment effectively alleviated CI symptoms of apricot by reducing the degradation rate. The enhanced chilling tolerance of apricot treated with MeSA could be affected by the increased sucrose content, which was regulated by the higher activities of sucrose phosphate synthase (SPS) and sucrose synthase-synthesis (SS-S), and the lower activities of acid invertase (AI), neutral invertase (NI) and sucrose synthase-cleavage (SS-C). We proposed that preharvest MeSA treatment could enhance the chilling tolerance by regulating sugar metabolism and further improve the postharvest quality of apricot during low temperature storage.

Suppression of sugar accumulation in coleoptile and mesocotyl cells by light irradiation to etiolated maize seedlings

Sugar accumulation in maize (Zea mays) coleoptile and mesocotyl cells was suppressed when etiolated seedlings were subjected to white light irradiation. Regulation mechanisms of sugar accumulation by light in cells of both organs were studied. Sucrose exudation from the endosperm was suppressed in light-treated seedlings. In addition, the activities and transcript levels of sucrose-phosphate synthase (SPS) in scutella were decreased following light irradiation. These results suggest that sucrose exudation from the endosperm is decreased by the suppression of SPS activities via downregulation of its gene expression. In coleoptiles and mesocotyls, light irradiation also decreased the activities and transcript levels of cell wall-bound invertase, suggesting that phloem unloading processes were suppressed. Thus, inhibition of both sucrose loading from the endosperm and sucrose unloading in coleoptiles and mesocotyls may be involved in the suppression of sugar accumulation in coleoptiles and mesocotyls irradiated with white light.

Enzymatic and transcriptomic analysis reveals the essential role of carbohydrate metabolism in freesia (Freesia hybrida) corm formation

Starch and sucrose metabolism plays a crucial role in the formation and development of bulbs in bulbous plants. However, these mechanisms remain unclear and unexplored in the corms of Freesia hybrida. Herein, we investigated the dynamics of the major form of carbohydrates and related enzyme activities and profiled the transcriptome of freesia corms at four developmental stages with the aim to reveal the relation between the expression of genes involved in the metabolism of carbohydrates and the accumulation of carbohydrates in corm developmental stages for further exploring the mechanism on the starch and sucrose metabolism regulating the formation and development of corms in F. hybrida. The content of starch, sucrose and soluble sugars followed an overall upward trend across the corm developmental stages. Activities of the adenosine diphosphoglucose pyrophosphorylase, starch branching enzyme and β-amylase generally followed the pattern of the starch and sucrose levels. Activities of sucrose phosphate synthase increased from corm formation till the initial swelling stage and subsequently reached a plateau. Activities of invertase and sucrose synthase peaked at the later rapid swelling stage. These suggested that the starch and sucrose dynamics paralleled corm swelling under the action of metabolic enzymes. A total of 100,999 unigenes were assembled in the transcriptomic analysis, and 44,405 unigenes of them were annotated. Analysis based on Clusters of Orthologous Groups suggested that carbohydrate transport and metabolism (9.34% of the sequences) was prominent across the corm developmental process. In total 3,427 differentially expressed genes (DEGs) were identified and the enrichment analysis detected starch and sucrose metabolism as a critical pathway in corm development, especially at the rapid swelling stage. Further, DEGs encoding key carbohydrate-metabolizing enzymes were identified and correlated to enzyme activities and carbohydrate accumulation. The results construct a valuable resource pool for further molecular-level studies, which are helpful for metabolic regulation of carbohydrates and improvement in F. hybrida.

Arbuscular Mycorrhiza Improves Photosynthesis and Restores Alteration in Sugar Metabolism in Triticum aestivum L. Grown in Arsenic Contaminated Soil.

Contamination of agricultural soil by arsenic (As) is a serious menace to environmental safety and global food security. Symbiotic plant–microbe interaction, such as arbuscular mycorrhiza (AM), is a promising approach to minimize hazards of As contamination in agricultural soil. Even though the potential of AM fungi (AMF) in redeeming As tolerance and improving growth is well recognized, the detailed metabolic and physiological mechanisms behind such beneficial effects are far from being completely unraveled. The present study investigated the ability of an AM fungus, Rhizophagus intraradices, in mitigating As-mediated negative effects on photosynthesis and sugar metabolism in wheat (Triticum aestivum) subjected to three levels of As, viz., 0, 25, and 50 mg As kg–1 of soil, supplied as sodium arsenate. As exposure caused significant decrease in photosynthetic pigments, Hill reaction activity, and gas exchange parameters such as net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration. In addition, As exposure also altered the activities of starch-hydrolyzing, sucrose-synthesizing, and sucrose-degrading enzymes in leaves. Colonization by R. intraradices not only promoted plant growth but also restored As-mediated impairments in plant physiology. The symbiosis augmented the concentration of photosynthetic pigments, enhanced Hill reaction activity, and improved leaf gas exchange parameters and water use efficiency of T. aestivum even at high dose of 50 mg As kg–1 of soil. Furthermore, inoculation with R. intraradices also restored As-mediated alteration in sugar metabolism by modulating the activities of starch phosphorylase, α-amylase, β-amylase, acid invertase, sucrose synthase, and sucrose-phosphate synthase in leaves. This ensured improved sugar and starch levels in mycorrhizal plants. Overall, the study advocates the potential of R. intraradices in bio-amelioration of As-induced physiological disturbances in wheat plant.

Nitrogen Levels Regulate Sugar Metabolism and Transport in the Shoot Tips of Crabapple Plants.

To comprehensively understand the responses of carbohydrate metabolism and transport to different levels of nitrogen supply in growing shoot tips of crabapple (Malus hupehensis Rehd), enzyme activities and related genes involved in the sugar metabolism pathway were investigated. The nitrogen and chlorophyll content of plants increased with increasing nitrogen supply. High nitrogen application increased the net photosynthesis rate and the growth rate of shoot tips but decreased the synthesis capability of sucrose and sorbitol in mature leaves. However, the shoot tips of plants under high-nitrogen treatment had higher contents of sucrose and sorbitol than did those under low-nitrogen treatment, while the activity of sucrose phosphate synthase and aldose-6-phosphate was increased and the transporters MdSOT and MdSUT were up-regulated. Moreover, the activities of enzymes involved in sucrose and hexose metabolism (including sucrose synthase, fructokinase, and hexokinase) were enhanced in the shoot tips of plants under high-nitrogen conditions, and the expression levels of MdSUSY3 and MdHK1 were significantly up-regulated. These findings indicate that a high nitrogen supply increases the metabolic capacity of assimilatory substances in shoot tips, accelerates the efficiency of sugar utilization and eventually leads to a rapid increase in the growth of shoot tips. Our results highlight that high nitrogen increases the capacity of sugar unloading and metabolic utilization in growing shoot tissues.

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.

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.

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.

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.

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.

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.

Underlying mechanism on source-sink carbon balance of grazed perennial grass during regrowth: Insights into optimal grazing regimes of restoration of degraded grasslands in a temperate steppe

Overgrazing is the main driver of grassland degradation and productivity reduction in northern China. The restoration of degraded grasslands depends on optimal grazing regimes that modify the source–sink balance to promote best carbon (C) assimilation and allocation, thereby promoting rapid compensatory growth of the grazed plants. We used in situ13CO2 labeling and field regrowth studies of Stipa grandis P.A. Smirn.to examine the effects of different grazing intensities (light, medium, heavy, and grazing exclusion) on photosynthetic C assimilation and partitioning, on reallocation of non-structural carbohydrates during regrowth, and on the underlying regulatory mechanisms. Light grazing increased the sink demand of newly expanded leaves and significantly promoted 13C fixation by increasing the photosynthetic capacity of the leaves and accelerating fructose transfer from the stem. Although C assimilation decreased under medium and heavy grazing, S. grandis exhibited a tolerance strategy that preferentially allocated more starch and 13C to the roots for storage to balance sink competition between newly expanded leaves and the roots. Sucrose phosphate synthase (SPS), sucrose synthase (SS), and other plant hormones regulated source–sink imbalances during regrowth. Abscisic acid promoted accumulation of aboveground biomass by stimulating stem SPS activity, whereas jasmonate increased root starch synthesis, thereby increasing belowground biomass. Overall, S. grandis could optimize source–sink relationships and above- and belowground C allocation to support regrowth after grazing by the regulating activities of SPS, SS and other hormones. These results provide new insights into C budgets under grazing and guidance for sustainable grazing management in semi-arid grasslands.

Effects of preharvest regulation of ethylene on carbohydrate metabolism of apple (Malus domestica Borkh cv. Starkrimson) fruit at harvest and during storage

The main purpose of this study was to investigate the effects of preharvest regulation of ethylene on apple fruit carbohydrate metabolism and quality at harvest and during storage. The positive regulation of ethylene was achieved by Ethephon, and the negative regulation was by Harvista, a kind of sprayable 1-methylcyclopropylene (1-MCP). ‘Starkrimson’ apple were treated with Harvista or Ethephon 7 d before harvest, respectively, and then stored at 0 °C for 180 d. The contents of starch, sucrose, glucose, fructose, and related enzymes activities and gene expression levels of sucrose phosphate synthase (SPS), sucrose synthase (SUSY), acid invertase (AINV), neutral invertase (NINV), cell wall invertase (CWINV) and amylase (AMY) were determined. The results showed that Harvista inhibited the starch degradation, retarded the increase of soluble sugar, reducing sugar, sucrose, glucose and fructose contents before 120 d of fruit storage, while no obvious difference was observed in these sugar content after 120 d of storage among three treatments. The enzyme activities of SPS, AINV, CWINV and AMY were also inhibited by Harvista at the early period of storage, and the expression levels of MdSPS, MdAINV, MdCWINV and MdAMY were positively correlated with their enzyme activities. In addition, Harvista reduced the fruit dropping rate at harvest and maintained the fruit firmness, while Ethephon showed the opposite effect. These results indicated that the preharvest regulation of ethylene effectively altered the carbohydrate metabolism and the quality of ‘Starkrimson’ apple fruit, and Harvista may be a useful tool applied at preharvest to maintain fruit quality at harvest and during storage.

Differences in carbon and nitrogen metabolism between male and female Populus cathayana in response to deficient nitrogen.

Sexual dimorphism occurs regarding carbon and nitrogen metabolic processes in response to nitrogen supply. Differences in fixation and remobilization of carbon and allocation and assimilation of nitrogen between sexes may differ under severe defoliation. The dioecious species Populus cathayana was studied after two defoliation treatments with two N levels. Males had a higher capacity of carbon fixation because of higher gas exchange and fluorescence traits of leaves after severe long-term defoliation under deficient N. Males had higher leaf abscisic acid, stomatal conductance and leaf sucrose phosphate synthase activity increasing transport of sucrose to sinks. Males had a higher carbon sink than females, because under N-deficient conditions, males accumulated >131.10% and 90.65% root starch than males in the control, whereas females accumulated >40.55% and 52.81%, respectively, than females in the control group. Males allocated less non-protein N (NNon-p) to leaves, having higher nitrogen use efficiency (photosynthetic nitrogen use efficiency), higher glutamate dehydrogenase (GDH) and higher leaf GDH expression, even after long-term severe defoliation under deficient N. Females had higher leaf jasmonic acid concentration and NNon-p. The present study suggested that females allocated more carbon and nitrogen to defense chemicals than males after long-term severe defoliation under deficient N.

Leaf carbohydrates assimilation and metabolism affect seed yield of rapeseed with different waterlogging tolerance under the interactive effects of nitrogen and waterlogging

AbstractWaterlogging is a main factor causing rapeseed (Brassica napus L.) yield loss, and reasonable nitrogen (N) applications can compensate for this loss. To investigate the effects of N rates on seed yield of waterlogged rapeseed, the waterlogging‐tolerant rapeseed variety ZS 9 and sensitive variety GH01 were waterlogged for 0 and 10 days with five leaves at the seedling stage under four N rates (0, 90, 180 and 270 kg/ha). Waterlogging significantly decreased seed yield, while N application can alleviate the yield loss. The yield decrease rate of waterlogged GH01 was greater than that of ZS 9 under the same N rate. During the seedling and bolting stage, the leaf photosynthetic rate (Pn) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) activity increased, while activities of adenosine diphosphate glucose pyrophosphorylase (AGPase), sucrose synthase (SuSy) and sucrose phosphate synthase (SPS) decreased with more N under the same watering conditions. Compared to the plants without waterlogging, the leaf Pn and Rubisco activity, starch and sucrose contents of waterlogged rapeseed decreased at the two stages; activities of AGPase, SuSy and SPS of waterlogged rapeseed decreased at the seedling while increased at the bolting stage for both the two varieties. At the flowering stage, the Pn, the activities of Rubisco, AGPase, SuSy, SPS and contents of sucrose, starch increased with more N application for both ZS 9 and GH01. Compared to the plants without waterlogging, the Pn and Rubisco activity for waterlogged plants of the two varieties increased; the waterlogged plants of tolerant variety had higher activities of AGPase, SuSy and SPS, while those of sensitive variety was significantly lower. However, the decreased starch and sucrose content were found in both tolerant and sensitive varieties. The activities of AGPase, SuSy and SPS at flowering were highly positively correlated with yield under the interactive effects of N and waterlogging. These results suggested that the flowering stage is the most important stage that N had the positive regulation on waterlogged rapeseed growth. The carbohydrates translocation from leaves to seeds of the tolerant variety were enhanced after waterlogging, while that of the sensitive variety was still inhibited. This was the main reason for the difference in yield between the two waterlogged varieties.

Effects of nitric oxide on nitrogen metabolism and the salt resistance of rice (Oryza sativa L.) seedlings with different salt tolerances

Salt stress inhibits rice productivity seriously. Nitric oxide (NO) is an endogenous signaling molecule in plants that can improve the resistance of rice to abiotic stresses. Previous studies also showed that nitrogen metabolism is essential for rice stress-tolerance. However, the physiological and molecular mechanisms by how NO affects the nitrogen metabolisms of rice seedlings remain unclear. A hydroponic experiment with two rice varieties, Jinyuan85 (salt tolerant) and Liaojing763 (salt sensitive), was carried out to explore whether NO could alleviate the negative effects of salt stress on nitrogen metabolism and increase salt resistance of rice seedlings. The results showed that (1) the application of NO alleviated the inhibitory effects of salt stress on plant height and biomass accumulation, and increased the nitrogen content of rice leaf. (2) the accumulation of the sucrose and proline was markedly increased in salt stress after application of NO, and peroxidase activities was increased by 107% and 67.7% for Jinyuan85 and Liaojing763, respectively. (3) NO significantly increased the activities of glutamate dehydrogenase, sucrose synthase and sucrose phosphate synthase in both rice varieties under salt stress. (4) Additionally, NO regulated the expression levels of AMT, NIA and SUT genes, but these regulation effects are different with rice varieties and treatments. The results suggested that NO mainly increased the glutamate dehydrogenase and peroxidase activities and sucrose accumulation to enhance the nitrogen metabolism and antioxidative capacity, and alleviated the negative effects of salt stress on rice performance.

Growth and carbohydrate dynamic of perennial ryegrass seedlings during PEG-simulated drought and subsequent recovery

Due to the increasing occurrence of drought events, drought recovery has become equally important as drought resistance for long-term growth and survival of plants. However, information regarding the mechanism that controls growth recovery of herbaceous perennials is not available. In this study, perennial ryegrass (Lolium perenne) was rewatered after eight-day exposure to three drought intensities simulated by polyethylene glycol-6000. The growth, nonstructural carbohydrates (NSC, i.e. sucrose, glucose, fructose and starch), shoot δ13C, and activities of enzymes for sucrose conversion were monitored for 24 days after rewatering, allowing investigation of the dynamic of NSCs and its relation with growth in the recovery phase. In response to drought, growth and NSC content decreased mainly in shoot rather than root, and the total dry matter was negatively correlated to shoot δ13C. After rewatering, the growth of drought-treated groups still lagged behind that of control (CK) group for more than 16 days, but it was no longer correlated to shoot δ13C, suggesting that the limited growth is caused by non-stomatal factors related to photosynthesis. On day 24 after rewatering, the final growth of drought-treated groups caught up or even exceeded that of CK group, and was accompanied by higher dry weight root to shoot ratio (R/S) and root NSC content, which may facilitate water and nutrient acquisition and emergency of new tillers, respectively. During drought and subsequent recovery, the variation of R/S and root NSC content mainly attributed to root acid invertase rather than leaf sucrose phosphate synthase activity.

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.

Leaf photosynthesis and CO2 assimilation in response to low nitrogen supply in bermudagrass (Cynodon dactylon (L.) Pers.)

Photosynthesis plays a vital role in maintaining vigorous, healthy turf under nitrogen (N)-limiting conditions. The effects of low N stress on the aboveground growth of bermudagrass (Cynodon dactylon (L.) Pers.) as well as its photosynthesis, chlorophyll fluorescence, CO2 assimilation, and carbohydrate pools were studied using hydroponic experiments. Two bermudagrass accessions, Yangjiang (low N tolerant) and C716 (low N sensitive), were used. Low N supply decreased the aboveground dry weight of both accessions. In comparison to C716, Yangjiang maintained better aboveground growth, which was attributed to its smaller reductions in leaf area and the net photosynthetic rate (Pn) at low N conditions. The Pn reduction in both accessions was on account of a reduction in stomatal conductance (Gs) and was partially due to nonstomatal limitations. Furthermore, the smaller Pn reduction in Yangjiang than in C716 was associated with the smaller decrease in CO2 assimilatory capacity in the former, and the ribulose-1,5-bisphosphate carboxylase (RuBisCO) and phosphoenolpyruvate carboxylase (PEPC) activities decreased based on leaf protein content. Although the leaf sucrose synthesis capacity and sucrose phosphate synthase (SPS) and sucrose synthase (SS) activities in Yangjiang increased more than those in C716, carbohydrates did not accumulate in the leaves of either accession to repress photosynthesis. This work provides new insights into CO2 assimilatory capacity rather than carbohydrate status under conditions of reduced leaf photosynthesis and decreasing aboveground growth in bermudagrass under low N conditions. Hence, bermudagrass accessions with low N tolerance are excellent sources of turf requiring reduced N fertilizer inputs.