Heat stress affects mammary metabolism by influencing the plasma flow to the glands

Background Environmental heat stress(HS)can have detrimental effects on milk production by compromising the mammary function.Mammary plasma flow(MPF)plays a crucial role in nutrient supply and uptake in the mam-mary gland.In this experiment,we investigated the physiological and metabolic changes in high-yielding cows exposed to different degrees of HS:no HS with thermal-humidity index(THI)below 68(No-HS),mild HS(Mild-HS,68≤THI≤79),and moderate HS(Mod-HS,79<THI≤88)in their natural environment.Our study focused on the changes in blood oxygen supply and mammary glucose uptake and utilization.Results Compared with No-HS,the MPF of dairy cows was greater(P<0.01)under Mild-HS,but was lower(P<0.01)in cows under Mod-HS.Oxygen supply and consumption exhibited similar changes to the MPF under different HS,with no difference in ratio of oxygen consumption to supply(P=0.46).The mammary arterio-vein differences in glucose concentration were lower(P<0.05)under Mild-and Mod-HS than under no HS.Glucose supply and flow were significantly increased(P<0.01)under Mild-HS but significantly decreased(P<0.01)under Mod-HS compared to No-HS.Glucose uptake(P<0.01)and clearance rates(P<0.01)were significantly reduced under Mod-HS compared to those under No-HS and Mild-HS.Under Mild-HS,there was a significant decrease(P<0.01)in the ratio of lac-tose yield to mammary glucose supply compared to that under No-HS and Mod-HS,with no difference(P=0.53)in the ratio of lactose yield to uptaken glucose among different HS situations.Conclusions Degrees of HS exert different influences on mammary metabolism,mainly by altering MPF in dairy cows.The output from this study may help us to develop strategies to mitigate the impact of different degrees of HS on milk production.

Transcriptome Sequencing for Sugar and Flavonoid Metabolism in Prunus persica‘Jinxiangyu’

In this study,high performance liquid chromatography(HPLC)and RNA-seq transcriptome sequencing were used to study the changes in soluble sugar components and flavonoids in Prunus persica‘Jinxiangyu’at different developmental stages(20–90 d after flowering)and screen the key genes regulating the formation of soluble sugar and flavonoids in the fruits.The results showed that 60–85 d after flowering was the key stage of quality formation of Prunus persica‘Jinxiangyu’,and the content of soluble sugar,soluble solid,fructose,and sucrose in the fruit increased significantly during this period.The sugar content of ripe fruits was mainly fructose and sucrose.The content of kaempferol glycoside was low in the fruit.Quercetin glycoside content was higher in the young fruit stage and decreased with fruit maturity.There were no anthocyanin compounds in the fruit.The expression levels of genes involved in flavonoid metabolism(ANS,DFR,F3H,FLS,4CL1,etc.)were low in the fruit.A total of 181 differentially expressed genes were identified during fruit development to participate in five sugar metabolism pathways,among which the SDH gene had a higher expression level,which continuously rised in the later stage of fruit development.It mainly promoted the accumulation of fructose content in the later stage of fruit development.The expression levels of SPS1,SS,and SS1 genes were continuously up-regulated,which played a key role in sucrose regulation.The higher expression levels of SUS3 and INVA genes in the early stage of fruit development promoted the degradation of sucrose.

Changes in Sugar Metabolism and Fruit Quality of Different Pear Cultivars During Cold Storage

This study evaluated the changes in sugar metabolism and fruit quality of diff erent pear cultivars during cold storage using seven major commercial pear cultivars belonging to diff erent Pyrus species, such as P. bretschneideri Rehd.("Huangguan,""Yali"), P. pyrifolia Nakai.("Wonhwang,""Hosui"), P. ussuriensis Maxim.("Jingbai,""Nanguo"), and P. communis L.("Bartlett"). The fi rmness, respiration rate, titratable acidity, total soluble solids, sugar content, and enzyme activity of the seven pear cultivars were investigated. SPSS was used for analyzing the signifi cance of diff erent indexes. Results showed that fructose was the dominant sugar, accounting for > 60% of total sugars, followed by glucose and sucrose. The respiration peak of almost all cultivars appeared within 60 days. The levels of fructose, glucose, sucrose, and total soluble solids increased within 90 days and then generally decreased. Acid invertase showed the highest activity among all pear cultivars, followed by neutral invertase, sucrose synthetase, and sucrose phosphate synthetase during storage.

Effects of Exogenous Trehalose on the Metabolism of Sugar and Abscisic Acid in Tomato Seedlings Under Salt Stress

Salt stress a ects the growth and development of plants, which results in a decrease in crop quality and yield. In this study, we used tomato seedlings treated with salt and trehalose as experimental materials and analyzed them using the technique for order preference by similarity to ideal solution analysis to select the optimal trehalose concentration for treatment. We also determined the contents of sugar and abscisic acid (ABA) and detected the expression of genes involved in the metabolism of sugar and ABA by quantitative real-time PCR. Results showed that the optimal trehalose concentration was 2 mmol/L for tomato seedlings under salt stress. Exogenous trehalose decreased the starch content and increased the soluble sugar con- tent by a ecting the expression of genes related to the metabolism of starch and soluble sugar. Exogenous trehalose altered the accumulation and distribution of sugar by inducing the upregulation of sugar transporter genes. Furthermore, trehalose increased the ABA content to induce salt stress response by regulating the expression of genes related to the synthesis and metabolism of ABA. In conclusion, trehalose can e ectively alleviate salt stress and enhance salt tolerance of tomato. These ndings provide a novel perspective and a better resource to investigate the salt tolerance mechanism and a new method for alleviating salt stress in tomato.

Identification of key gene networks controlling organic acid and sugar metabolism during watermelon fruit development by integrating metabolic phenotypes and gene expression profiles

The organoleptic qualities of watermelon fruit are defined by the sugar and organic acid contents,which undergo considerable variations during development and maturation.The molecular mechanisms underlying these variations remain unclear.In this study,we used transcriptome profiles to investigate the coexpression patterns of gene networks associated with sugar and organic acid metabolism.We identified 3 gene networks/modules containing 2443 genes highly correlated with sugars and organic acids.Within these modules,based on intramodular significance and Reverse Transcription Quantitative polymerase chain reaction(RT-qPCR),we identified 7 genes involved in the metabolism of sugars and organic acids.Among these genes,Cla97C01G000640,Cla97C05G087120 and Cla97C01G018840(r^(2)=0.83 with glucose content)were identified as sugar transporters(SWEET,EDR6 and STP)and Cla97C03G064990(r^(2)=0.92 with sucrose content)was identified as a sucrose synthase from information available for other crops.Similarly,Cla97C07G128420,Cla97C03G068240 and Cla97C01G008870,having strong correlations with malic(r^(2)=0.75)and citric acid(r^(2)=0.85),were annotated as malate and citrate transporters(ALMT7,CS,and ICDH).The expression profiles of these 7 genes in diverse watermelon genotypes revealed consistent patterns of expression variation in various types of watermelon.These findings add significantly to our existing knowledge of sugar and organic acid metabolism in watermelon.

Gene Expression and Activity of Enzymes Involved in Sugar Metabolism and Accumulation During “Huangguan” and “Yali” Pear Fruit Development

Since the carbohydrate content affects pear flavor during the process of growth, it is necessary to determine the sugar components that accumulate in the fruit. We analyzed the fruit carbohydrate content, and the gene expression and activity ofacid invertase(AI), neutral invertase(NI), sucrose synthase(SS), and sucrose phosphate synthase(SPS) during the development of "Huangguan" and "Yali" pears. The results demonstrate that during development, the fruit sugar metabolism of the "Huangguan" pear follows a typical sorbitol–starch-soluble sugars middle model, whereas the "Yali" pear fruit follows a typical sorbitol–sucrose–starch-soluble sugars middle model. In the "Huangguan" pear, we found the AI and NI gene expressions, as well as AI( P < 0.05) and NI( P < 0.01) enzyme activities, to be positively correlated, whereas we found the NI gene expression and NI enzyme activity of "Yali" pear to be negatively correlated( P < 0.01). We observed the high levels oflate-stage AI and early-stage SS during development to roughly correspond with the gene expression found in the late and early stages, respectively, suggesting their potential regulatory roles in "Huangguan" pear fruit development. Our results indicate that the primary function of SPS during the early developmental stage is to accumulate sucrose, whereas the primary function of AI is to promote hexose accumulation during the late developmental stage ofmature "Yali" pear fruit.

Effects of water stress on quality and sugar metabolism in'Gala'apple fruit

Sugar plays an important role in apple fruit development,appearance and quality as well as contributing to a plant’s water stress response.Trehalose and the trehalose biosynthetic metabolic pathways are part of the sugar signaling system in plants,which are important regulator of water stress response in apple.The effect of water stress treatments applied to apple trees and the corresponding effects of ABA on developmental fruit quality were examined for indicators of fruit quality during fruit development.The results indicated that the severe water stress treatment(W2)occurring after the last stage of fruit cell division caused a decrease in the color and size of fruit.The moderate water stress(W1)occurring after the last stage of fruit cell enlargement(S2)caused an increase in the content of fructose and sorbitol while the apple fruit shape was not affected.These changes in sugar are related to the activity of sugar metabolic enzymes.While the enzymatic activity of vacuolar acid invertase(vAINV)was higher,that of sucrose-phosphate synthase(SPS)was lower in water stress treated fruit throughout the developmental period.This indicates that enhanced sucrose degradation and reduced sucrose synthesis leads to an overall reduced sucrose content during times of drought.Thus,water stress reduced sucrose content.Whereas the content of endogenous trehalose and ABA were the highest in water stress treated fruit.A moderate water stress(W1)imposed on apple trees via water restriction(60%–65%of field capacity)after the fruit cell enlargement phase of fruit development yielded sweeter fruit of higher economic value.

The essential roles of sugar metabolism for pollen development and male fertility in plants

Sugar metabolism plays an essential role in plant male reproduction. Defects in sugar metabolism during anther and pollen development often result in genic male sterility(GMS). In this review, we summarize the recent progresses of the sugar metabolism-related GMS genes and their roles during plant anther and pollen development, including callose wall and primexine formation, intine development, pollen maturation and starch accumulation, anther dehiscence, and pollen germination and tube growth. We predict 112 putative sugar metabolic GMS genes in maize based on bioinformatics and RNA-seq analyses, and most of them have peak expression patterns during middle or late anther developmental stages.Finally, we outline the potential applications of sugar metabolic GMS genes in crop hybrid breeding and seed production. This review will deepen our understanding on sugar metabolic pathways in controlling pollen development and male fertility in plants.

Transcriptomics-based identification and characterization of genes related to sugar metabolism in‘Hongshuijing’pitaya

Sugar composition not only affects fruit flavor but is also an important determinant of fruit taste and consumer preference.In this study,changes in the sugar content and sugar-metabolizing enzymes were investigated from different sections of various fruit development phases of‘Hongshuijing’pitaya(Hylocereus monacanthus).Genes related to sugar metabolism were also screened by transcriptome analyses.The results indicated that glucose was the major sugar in mature pitaya fruit,and was mainly regulated by vacuolar acid invertase(VAI)and sucrose synthase(SS)(degradative direction).Sugar accumulation varied in pulp between different sections of the pitaya fruit.VAI,neutral invertase(NI)and SS(degradative direction)are crucial enzymes for sugar accumulation in pitaya.The expression of 17 genes related to sucrose metabolism obtained from seven databases[NCBI non-redundant protein database(Nr),NCBI non-redundant nucleotide sequence database(Nt),EuKaryotic Orthologous Groups(KOG),The Protein Families(Pfam),Kyoto Encyclopedia of Genes and Genomes(KEGG),Swiss-prot,and Gene Ontology(GO)]were analyzed in different pitaya pulp sections.HpVAI1 had the highest relative expression level on the 29th day after pollination(DAP).Positive correlations were found between HpVAI1 expression and VAI activity;HpNI4 and NI activity;HpSS2,HpSS5,and SS activity(synthetic direction),indicating that HpVAI1,HpNI4,and HpSS2 and HpSS5 were involved in the regulation of VAI,NI,and SS(synthetic direction),respectively.HpVAI1 and HpNI4 regulated sucrose degradation and the accumulation of glucose and fructose,while HpSS2 and HpSS5 regulated sucrose synthesis.These results suggest that HpVAI1 plays a key role in sugar metabolism during fruit development of‘Hongshuijing’pitaya.The results of this study provide new information about sugar metabolism in pitaya fruit that could help improve fruit quality and the breeding of new cultivars.

Potassium deficiency inhibits steviol glycosides synthesis by limiting leaf sugar metabolism in stevia(Stevia rebaudiana Bertoni)plants

The steviol glycosides(SGs)in stevia(Stevia rebaudiana Bertoni)leaves are becoming increasingly valuable due to its high sweetness but low calorific value,which is driving the development of stevia commercial cultivation.Optimizing fertilization management can effectively increase SGs productivity,but knowledge on the relationship between potassium(K)fertilization and SGs production is still lacking.In this study,pot experiments were conducted in order to investigate the effect of K deficiency on SGs synthesis in stevia leaves,as well as the underlying mechanisms.Our results showed that when compared with standard K fertilization,K deficiency treatment has no significant effect on the biomass of stevia plant grown in a given soil with high K contents.However,K deficiency critically decreased leaf SGs contents as well as the expression of SGs synthesis-related genes.The contents of different sugar components decreased and the activities of sugar metabolism-related enzymes were inhibited under the K deficiency condition.Moreover,spraying sucrose on the leaves of stevia seedlings diminished the inhibitory effect caused by K deficiency.Our results also revealed the significant positive correlations between sucrose,glucose and SGs contents.Overall,our results suggest that K deficiency would suppress the synthesis of SGs in stevia leaves,and this effect may be mediated by the leaf sugar metabolism.Our findings provide new insights into the improvement of SGs production potential.

Brassica rapa orphan genes largely affect soluble sugar metabolism

Orphan genes(OGs),which are genes unique to a specific taxon,play a vital role in primary metabolism.However,little is known about the functional significance of Brassica rapa OGs(BrOGs)that were identified in our previous study.To study their biological functions,we developed a BrOG overexpression(BrOGOE)mutant library of 43 genes in Arabidopsis thaliana and assessed the phenotypic variation of the plants.We found that 19 of the 43 BrOGOE mutants displayed a mutant phenotype and 42 showed a variable soluble sugar content.One mutant,BrOG1OE,with significantly elevated fructose,glucose,and total sugar contents but a reduced sucrose content,was selected for indepth analysis.BrOG1OE showed reduced expression and activity of the Arabidopsis sucrose synthase gene(AtSUS);however,the activity of invertase was unchanged.In contrast,silencing of two copies of BrOG1 in B.rapa,BraA08002322(BrOG1A)and BraSca000221(BrOG1B),by the use of an efficient CRISPR/Cas9 system of Chinese cabbage(B.rapa ssp.campestris)resulted in decreased fructose,glucose,and total soluble sugar contents because of the upregulation of BrSUS1b,BrSUS3,and,specifically,the BrSUS5 gene in the edited BrOG1 transgenic line.In addition,we observed increased sucrose content and SUS activity in the BrOG1 mutants,with the activity of invertase remaining unchanged.Thus,BrOG1 probably affected soluble sugar metabolism in a SUS-dependent manner.This is the first report investigating the function of BrOGs with respect to soluble sugar metabolism and reinforced the idea that OGs are a valuable resource for nutrient metabolism.

Regulation of Growth, Antioxidants and Sugar Metabolism in Rice (Oryza sativa L.) Seedlings by NaCl and Its Reversal by Silicon

The effect of NaCl with or without silicon on the growth and metabolism in rice seedlings cv. MTU1010 was studied. In these seedlings, the oxidative stress has been observed with NaCl treatments and the levels of proline, H2O2 and malondialdehyde contents were increased whereas catalase activity was decreased. NaCl exposure at 25 mM, 50 mM and 100 mM concentrations in the test seedlings resulted in an increase in both reducing and non-reducing sugar content. There was a decrease in starch contents and the activity of starch phosphorylase was increased. NaCl stress also affected the activities of different carbohydrate metabolizing enzymes. The activities of sucrose synthase and sucrose phosphate synthase were increased, while the activity of acid invertase was decreased. Joint application of silicon with NaCl showed significant alterations on all parameters tested under the purview of NaCl treatment alone leading to better growth and metabolism in rice seedlings. Thus the use of silicon enriched fertilizers may help to grow healthy rice plants in NaCl rich soil.

Effects of bone marrow mesenchymal stem cell combined with platelet-rich plasma treatment of bone nonunion after long bone fracture surgery on bone metabolism and cytokines

Objective: To study the effects of bone marrow mesenchymal stem cell combined with platelet-rich plasma treatment of bone nonunion after long bone fracture surgery on bone metabolism and cytokines. Methods: Patients who were treated in our hospital due to bone nonunion after long bone fracture surgery between March 2011 and October 2017 were selected and randomly divided into two groups, combined group received bone marrow mesenchymal stem cell combined with platelet-rich plasma therapy, and control group received bone marrow mesenchymal stem cell therapy. The levels of bone metabolism markers and growth cytokines in serum as well as the expression of bone metabolism-related signal molecules in peripheral blood were determined before treatment and 1 month after treatment. Results: Compared with those of same group before treatment, serum PINP, OPG, BALP, VEGF, TGF-β1, IGF-I, IGF-II and bFGF levels as well as peripheral blood Runx2, Wnt1, Wnt3a and β-catenin expression intensity of both groups of patients significantly increased whereas serum β-CTX and RANKL levels as well as peripheral blood NOX4 and NF-κB expression intensity significantly decreased after treatment, and serum PINP, OPG, BALP, VEGF, TGF-β1, IGF-I, IGF-II and bFGF levels as well as peripheral blood Runx2, Wnt1, Wnt3a and β-catenin expression intensity of combined group after treatment were higher than those of control group whereas serum β-CTX and RANKL levels as well as peripheral blood NOX4 and NF-κB expression intensity were lower than those of control group. Conclusion: Bone marrow mesenchymal stem cell combined with platelet-rich plasma treatment of bone nonunion after long bone fracture surgery can be more effective than bone marrow mesenchymal stem cell monotherapy to improve the bone metabolism and increase the cytokines.

EFFECT OF ACUPUNCTURE ON CARBOHYDRATE METABOLISM IN PATIENTS WITH SIMPLE OBESITY

In an attempt to elucidate the effect ofacupuncture on carbohydrate metabolism inpatients with simple obesity and its mecha-nism in reducing excess body fat,obesity in-dexes,fasting blood sugar,insulin contentand activity of lactic dehydrogenase(LDH)were all observed before and afteracupuncture treatment.

Effects research of different capacity exercise on fat metabolism

Fatty is one of the most important energy storage substances in the human body, and is an important source of energy in motion. It has 10 times bigger storage space than glycogen. Some studies suggest that in low to moderate intensity aerobic exercise, fat plays an important role providing energy. Especially when the movement lasts for more than 3 ~ 4h, energy provided by fat can account for 70% to 90% of total energy metabolism. Many people use many means and methods in order to increase the proportion of fat oxidation providing for energy in the movement and save glucose consumption in vivo, improving the body＇ s endurance. On the other hand, endurance exercise can burn fat properly, and play an important role to reduce accumulation of body fat, prevent hyperlipidemia and improve lipid levels.

Vitamin B1 THIAMIN REQUIRING1 synthase mediates the maintenance of chloroplast function by regulating sugar and fatty acid metabolism in rice

Vitamin B(VB1),including thiamin,thiamin monophosphate(TMP),and thiamin pyrophosphate(TPP),is an essential micronutrient for all living organisms.Nevertheless,the precise function of VB1 in rice remains unclear.Here,we described a VB1 auxotrophic mutant,chlorotic lethal seedling(cles)from the mutation of OsTH1,which displayed collapsed chloroplast membrane system and decreased pigment content.OsTH1 encoded a phosphomethylpyrimidine kinase/thiamin-phosphate pyrophosphorylase,and was expressed in various tissues,especially in seedlings,leaves,and young panicles.The VB1 content in cles was markedly reduced,despite an increase in the expression of VB1 synthesis genes.The decreased TPP content affected the tricarboxylic acid cycle,pentose phosphate pathway,and de novo fatty acid synthesis,leading to a reduction in fatty acids(C16:0 and C18:0)and sugars(sucrose and glucose)of cles.Additionally,irregular expression of chloroplast membrane synthesis genes led to membrane collapse.We also found that alternative splicing and translation allowed OsTH1 to be localized to both chloroplast and cytosol.Our study revealed that OsTH1 was an essential enzyme in VB1 biosynthesis and played crucial roles in seedling growth and development by participating in fatty acid and sugar metabolism,providing new perspectives on VB1 function in rice.

Sugar Input, Metabolism, and Signaling Mediated by Invertase： Roles in Development, Yield Potential, and Response to Drought and Heat

Invertase （INV） hydrolyzes sucrose into glucose and fructose, thereby playing key roles in primary metabolism and plant development. Based on their pH optima and sub-cellular locations, INVs are categorized into cell wall, cytoplasmic, and vacuolar subgroups, abbreviated as CWlN, CIN, and VlN, respectively. The broad importance and implications of INVs in plant development and crop productivity have attracted enormous interest to examine INV function and regulation from multiple perspectives. Here, we review some exciting advances in this area over the last two decades, focusing on （1） new or emerging roles of INV in plant development and regulation at the post-translational level through interaction with inhibitors, （2） cross-talk between INV-mediated sugar signaling and hormonal control of development, and （3） sugar- and INV-mediated responses to drought and heat stresses and their impact on seed and fruit set. Finally, we discuss major questions arising from this new progress and outline future directions for unraveling mechanisms underlying INV-mediated plant development and their potential applications in plant biotechnology and agriculture.

Difference of a citrus late-ripening mutant (Citrus sinensis) from its parental line in sugar and acid metabolism at the fruit ripening stage

‘Fengjiewancheng’(FW) (Citrus sinensis), a bud sport of‘Fengjie 72-1’navel orange (FJ), ripens one month later than its parental line. Differences in sugar and acid content and the transcript level of su-crose- and citric-metabolic enzymes for the two cultivars were investigated during fruit ripening. Re-sults showed that both sugar and acid metabolisms of the mutant were affected by the mutation. In the pulp of FW, sugar content was significantly lower than that in FJ before 227 DAF (days after flowering) and higher at 263 DAF; the mutant’s gene expression of one isoform of citrus sucrose synthase (CitSS1) was delayed, and its gene expression of citrus acid invertase (CitAI) was stronger than that in its pa-rental cultivars at 207 and 263 DAF. In the peel, only the sucrose content in FW was significantly lower than those in FJ at the early periods of fruit ripening (165 and 187 DAF); however the transcripts of the sucrose-cleaving enzymes in the mutant were higher than those in FJ at different ripening points. As regards acid accumulation in the two cultivars, it was observed that in the pulp of the mutant, the malic acid content was significantly lower than that in its parental cultivars from 187 to 263 DAF, and in the peel, remarkably higher during the whole fruit ripening period. The citric acid content in both the pulp and the peel of FW was higher than that in those of FJ during the early ripening period and lower during the late ripening period, which were correspondingly associated in part with the higher transcript level of citrus mitochondrial citrate synthase (CitCS) and with lower or undetectable transcript level of citrus cytosolic aconitase (CitAC). Hence, it could be concluded that the mutation in FW affected sugar and acid metabolism, which might be related with other late-ripening phenotypes.

AKINβ1 is Involved in the Regulation of Nitrogen Metabolism and Sugar Signaling in Arabidopsis

Sucrose non-fermenting-l-related protein kinase 1 （SnRK1） has been located at the heart of the control of metabolism and development in plants. The active SnRK1 form is usually a heterotrimeric complex. Subcellular localization and specific target of the SnRK1 kinase are regulated by specific beta subunits. In Arabidopsis, there are at least seven genes encoding beta subunits, of which the regulatory functions are not yet clear. Here, we tried to study the function of one beta subunit, AKINβ1. It showed that AKINβ1 expression was dramatically induced by ammonia nitrate but not potassium nitrate, and the investigation of AKINβ1 transgenic Arabidopsis and T-DNA insertion lines showed that AKINβ1 negatively regulated the activity of nitrate ruductase and was positively involved in sugar repression in early seedling development. Meanwhile AKIN/β1 expression was reduced upon sugar treatment （including mannitol） and did not affect the activity of sucrose phosphate synthase. The results indicate that AKIN/β1 is involved in the regulation of nitrogen metabolism and sugar signaling.

Role of rice cytosolic hexokinase OsHXK7 in sugar signaling and metabolism

We characterized the function of the rice cytosolic hexokinase OsHXK7 （Qryza sativa HexokindseZ）, which is highly upregulated when seeds germinate under O2- deficient conditions. According to transient expression assays that used the promoter：luciferase fusion construct, OsHXK7 enhanced the glucose （Glc）-dependent repression of a rice n-amylase gene （RAmy3D） in the mesophyll protoplasts of maize, but its catalytically inactive mutant alleles did not. Consistently, the expression of OsHXK7, but not its catalytically inactive alleles, complemented the Arabidopsis glucose insensitive2-1 （gin2-1） mutant, thereby resulting in the wild type characteristics of Glc-dependent repression, seedling development, and plant growth. Interestingly, OsHXK7-mediated Glc-dependent repression was abolished in the O2-deficient mesophyll protoplasts of maize. This result provides compelling evidence that OsHXK7 functions in sugar signaling via a glycolysis-dependent manner under normal conditions, but its signaling role is suppressed when O2 is deficient. The germination of two null OsHXK7 mutants, oshxk7-1 and oshxk7-2, was affected by O2 deficiency, but overexpression enhanced germination in rice. This result suggests the distinct role that OsHXK7 plays in sugar metabolism and efficient germination by enforcing glycolysis-mediated fermentation in O2-deficient rice.