Aldo-keto reductase family member C3(AKR1C3)promotes hepatocellular carcinoma cell growth by producing prostaglandin F2α

Hepatocellular carcinoma(HCC)is a leading cause of death worldwide.Current therapies are effective for HCC patients with early disease,but many patients suffer recurrence after surgery and have a poor response to chemotherapy.Therefore,new therapeutic targets are needed.We analyzed gene expression profiles between HCC tissues and normal adjacent tissues from public databases and found that the expression of genes involved in lipid metabolism was significantly different.The analysis showed that AKR1C3 was upregulated in tumors,and high AKR1C3 expression was associated with a poorer prognosis in HCC patients.In vitro,assays demonstrated that the knockdown of AKR1C3 or the addition of the AKR1C3 inhibitor indomethacin suppressed the growth and colony formation of HCC cell lines.Knockdown of AKR1C3 in Huh7 cells reduced tumor growth in vivo.To explore the mechanism,we performed pathway enrichment analysis,and the results linked the expression of AKR1C3 with prostaglandin F2 alpha(PGF2a)downstream target genes.Suppression of AKR1C3 activity reduced the production of PGF2a,and supplementation with PGF2a restored the growth of indomethacin-treated Huh7 cells.Knockdown of the PGF receptor(PTGFR)and treatment with a PTGFR inhibitor significantly reduced HCC growth.We showed that indomethacin potentiated the sensitivity of Huh7 cells to sorafenib.In summary,our results indicate that AKR1C3 upregulation may promote HCC growth by promoting the production of PGF2α,and suppression of PTGFR limited HCC growth.Therefore,targeting the AKR1C3-PGF2a-PTGFR axis may be a new strategy for the treatment of HCC.

Aldo-keto reductases:Role in cancer development and theranostics

Aldo-keto reductases(AKRs)are a superfamily of enzymes that play crucial roles in various cellular processes,including the metabolism of xenobiotics,steroids,and carbohydrates.A growing body of evidence has unveiled the involvement of AKRs in the development and progression of various cancers.AKRs are aberrantly expressed in a wide range of malignant tumors.Dysregulated expression of AKRs enables the acquisition of hallmark traits of cancer by activating oncogenic signaling pathways and contributing to chemoresistance.AKRs have emerged as promising oncotherapeutic targets given their pivotal role in cancer development and progression.Inhibition of aldose reductase(AR),either alone or in combination with chemotherapeutic drugs,has evolved as a pragmatic therapeutic option for cancer.Several classes of synthetic aldo-keto reductase(AKR)inhibitors have been developed as potential anticancer agents,some of which have shown promise in clinical trials.Many AKR inhibitors from natural sources also exhibit anticancer effects.Small molecule inhibitors targeting specific AKR isoforms have shown promise in preclinical studies.These inhibitors disrupt the activation of oncogenic signaling by modulating transcription factors and kinases and sensitizing cancer cells to chemotherapy.In this review,we discuss the physiological functions of human AKRs,the aberrant expression of AKRs in malignancies,the involvement of AKRs in the acquisition of cancer hallmarks,and the role of AKRs in oncogenic signaling,and drug resistance.Finally,the potential of aldose reductase inhibitors(ARIs)as anticancer drugs is summarized.

Synthesis and Characterization of Naproxen-Salicylate Derivatives as Potential Dual-Targeted Inhibitors of Dihydrofolate Reductase

Dihydrofolate reductase (DHFR) is an enzyme that catalyzes the reduction of dihydrofolate (DHF) to tetrahydrofolate (THF). Chemotherapy drugs such as methotrexate help to slow the progression of cancer by limiting the ability of dividing cells to make nucleotides by competitively inhibiting DHFR. Nonsteroidal anti-inflammatory drugs (NSAIDs) have been previously reported to exhibit competitive inhibition of DHFR, in addition to their primary action on cyclooxygenase enzymes. This interaction interferes with the enzymatic reduction of dihydrofolate to tetrahydrofolate, thereby impeding the folate metabolism pathway essential for nucleotide synthesis and cell proliferation. This activity stems from their structural resemblance to the p-aminobenzoyl-l-glutamate (pABG) moiety of folate, a substrate of DHFR. It has been established that NSAIDs containing a salicylate group (which has structural similarities to pABG), such as diflunisal, exhibit stronger DHFR-binding activity. In this study, we synthesized salicylate derivatives of naproxen with the aim of exploring their potential as inhibitors of DHFR. The interactions between these derivatives and human DHFR were characterized using a combination of biochemical, biophysical, and structural methods. Through polyacrylamide gel electrophoresis (PAGE) analysis, enzymatic assays, and quantitative ELISA, we investigated the binding affinity and inhibitory potency of the synthesized salicylate derivatives towards DHFR. The findings of this study suggest the potential of salicylate derivatives of naproxen as promising candidates for the inhibition of DHFR, thereby offering novel therapeutic opportunities for modulating the inflammatory process through multiple pathways. Further optimization of these derivatives could lead to the development of more efficacious dual-targeted analogs with enhanced therapeutic benefits.

Cloning and Expression Analysis of Two Wheat cDNAs Encoding Cinnamoyl-CoA Reductase

Cinnamoyl-CoA reductase (CCR) is responsible for the first committed reaction in monolignol biosynthesis, which diverts phenylpropanoid-derived metabolites into the biosynthesis of lignin. To gain a better understanding of the lion biosynthesis in wheat development, two cDNAs encoding CCR were identified from wheat (Triticum aestivum L. cv. H4564). DNA sequence analyses indicated that the two cDNAs represent two classes of CCR. RT-PCR and Northern blot hybridization demonstrated that one of them, W-cr6, was expressed actively in stem and leaf tissue, the other one, W-cr19, was expressed in root and stem tissue. The results suggested that there are at least two genes encoded for CCR existing in wheat genome.

Cloning and Bioinformatic Analysis of Cinnamoyl-CoA Reductase Gene (CCR) from Pennisetum purpureum

[Objective] The aim was to clone the cDNA and DNA sequences of the CCR （Cinnamoyl-CoA reductase） gene which involves in lignin biosynthesis, from Pennisetum purpureum, and to make comprehensive analysis on these sequences. [Method] CCR sequences were cloned from P. purpureum by using conventional RT-PCR and RACE （Rapid Amplification of cDNA Ends） methods; and the bioinformatic analyses of the CCR were conducted by means of NCBI, ProtParam ProtScale, TMHMM, TargetP, SignalP, Pfam20.0, Prosite, Swiss-Model, ClustalW2, DNAman, DNAstar and MEGA5. [Result] The cloned PpCCR （P. purpureum CCR） cDNA sequence was 1 316 bp, including a 1 110 bp ORF and 206 bp 3’-UTR. The cloned DNA sequence from PpCCR was 6 133 bp in full-length, containing five exons and four introns. Bioinformatic analysis indicated that PpCCR encoded a polypeptide of 369 amino acids, the secondary structure of which was primarily composed of random coil and α-helix, belonging to NAD-dependent epimerase/dehydratase family, and its co-factor binding sites and substrate binding sites were highly conserved. [Conclusion] DNA and cDNA sequences of CCR gene were obtained from P. purpureum, which had the typical characteristics of other homologous genes. The obtained bioinformatic data provided theoretical references for the further analysis of CCR and better application of P. purpureum in the future.

Nitrate reductase activity and its diurnal variation rhythm for Camptotheca acuminata seedlings

Nitrate reductase activity (NRA) in different plant organs and leaves in different positions of Camptotheca acuminata seedlings was determined by an In vivo assay, the diurnal variation rhythm of NRA in leaves of different positions was observed,and the correlations between leaf NRA, leaf area and lamina mass per unit area (LMA) were also examined. The results showed that NRA in the leaf was significantly highest, compared with that in other organs such as roots, stems and leaves. In this experiment, the 10 leaves were selected from the apex to the base of the seedlings in order. The different NRA occurred obviously in leaves of different positions of C. acuminata seedlings from the apex to the base, and NRA was higher in the 4th-6th leaves.The diurnal change rhythm of leaf NRA showed a one peak curve, and maximum NRA value appeared at about midday (at 12:30 or so). No obvious correlations between NRA and leaf area or lamina mass per unit area were observed. This study offered scientific foundation for the further research on nitrogen metabolism of C. acuminata.

多枝赖草Glutathione Reductase基因克隆及胁迫表达分析

为了获得完整的谷胱甘肽还原酶基因序列,根据已克隆到的谷胱甘肽还原酶cDNA片段设计引物,利用RACE扩增获得了基因全长序列,应用Southern印迹杂交法分析基因存在状态,Northern印迹杂交法研究基因表达情况.结果表明,该基因全长1580 bp,含一个1 140 bp的开放阅读框架,编码380个氨基酸,与其它植物谷胱甘肽还原酶氨基酸序列的同源性在77%-92%之间;Southern杂交表明该基因有一个拷贝;Northern杂交表明在逆境胁迫下GR基因表达加强.

油菜素内酯合成酶(Steroid 5α-Reductase)基因的超量表达对毛白杨生长的影响

将棉花Steroid 5α-reductase基因(DET2)超量表达载体导入毛白杨中,观察其对毛白杨生长和芽休眠的影响。结果表明,超量表达DET2基因的毛白杨茎高度、直径生长和不定根的生长增强,芽的休眠破除提前。

Dynamic Changes of Nitrate Reductase Activity within 24 Hours

[Objective] The research aimed to study the circadian rhythm of nitrate re- ductase activity （NRA） in plant. [Method] The wheat plants at heading stage were used as the materials for the measurement of dynamic changes of nitrate reductase activity （NRA） within 24 h under the conditions of constant high temperature. [Resulti The fluctuation of NRA in wheat changed greatly from 20：00 pm to 11：00 am. The enzyme activity remained constant, but at 14：00 the enzyme activity was the high- est, higher than all the other time points except the enzyme activity measured at11：00. The enzyme activity was the lowest of 17：00, which was lower than all the other time points except the enzyme activity measured at 2：00. [Conclusion] There were autonomous rhythm changes of NRA in wheat in a certain degree.

Women with Methylenetetrahydrofolate Reductase Gene Polymorphism and the Need for Proper Periconceptional Folate Supplementation

Maternal folate supplementation is critical for fetal development. Women with MTHFR （methylenetetrahydrofolate reductase） gene polymorphisms may not be getting the proper folate form to support fetal development. The objectives of this review were to： （1） undertake a comprehensive review on the association of MTHFR polymorphisms with the risk for various congenital diseases and other adverse pregnancy outcomes, （2） assess the efficacy and safety of current folic acid and other supplementations in women with the MTHFR polymorphism, and （3） provide guidance on the appropriate supplementation for women of childbearing potential with the MTHFR gene polymorphism in order to decrease these adverse pregnancy outcomes. Our assessments show that women with MTHFR gene polymorphism cannot efficiently convert folic acid to L-5-methyl-tetrahydofolate, the predominant active form of folic acid, due to reduced MTHFR enzymatic activity. L-5-methyl-tetrahydrofolate is currently commercially available under several brand names. Based on our comprehensive review and knowledge of the biochemistry of the folates, we recommend that L-5-methyltetrahydrofolate be given in combination with folic acid to women with MTHFR polymorphism that are pregnant or planning to become pregnant. Further study is needed to determine the optimal dose.

Feedback regulation of cholesterol synthesis： sterol-accelerated ubiquitination and degradation of HMG CoA reductase

3-Hydroxy-3-methylglutaryl coenzyme A （HMG CoA） reductase produces mevalonate, an important intermediate in the synthesis of cholesterol and essential nonsterol isoprenoids. The reductase is subject to an exorbitant amount of feedback control through multiple mechanisms that are mediated by sterol and nonsterol end-products of mevalonate metabolism. Here, I will discuss recent advances that shed light on one mechanism for control of reductase, which involves rapid degradation of the enzyme. Accumulation of certain sterols triggers binding of reductase to endoplasmic reticulum （ER） membrane proteins called Insig-1 and Insig-2. Reductase-Insig binding results in recruitment of a membrane-associated ubiquitin ligase called gp78, which initiates ubiquitination of reductase. This ubiquitination is an obligatory reaction for recognition and degradation of reductase from ER membranes by cytosolic 26S proteasomes. Thus, sterol-accelerated degradation of reductase represents an example of how a general cellular process （ER-associated degradation） is used to control an important metabolic pathway （cholesterol synthesis）.

Single nucleotide polymorphism C677T in the methylenetetrahydrofolate reductase gene might be a genetic risk factor for infertility for Chinese men with azoospermia or severe oligozoospermia

Aim： To analyze the distribution of the single nucleotide polymorphism （SNP） C677T in the methylenetetrahydrofolate reductase （MTHFR） gene in 355 infertile Chinese patients with idiopathic azoospermia or severe oligozoospermia and 252 fertile Chinese men as controls to explore the possible association of the SNP and male infertility. Methods： Using the polymerase chain reaction （PCR）-restriction fragment length polymorphism technique, the allele and genotype distribution of SNP C677T in the MTHFR gene were investigated in both patients and controls. Results： The frequencies of allele T （40.9% vs 30.4%, P = 0.002, odds ration [OR] = 1.58, 95% confidence interval [CI]： 1.24-2.02） and mutant homozygote （TT） （18.3% vs. 11.5%, P = 0.023, OR = 1.72, 95% CI： 1.07-2.76） as well as carrier with allele （TT ＋ CT） （63.4% vs. 49.2%, P = 0.0005, OR = 1.79, 95% CI： 1.29-2.48） in infertile patients were significantly higher than those in controls. After patient stratification, the significant differences in distribution of the SNP between each patient subgroup and control group still remained. Conclusion： Our findings indicate that there is an association of SNP C677T in the MTHFR gene with male infertility, suggesting that this polymorphism might be a genetic risk factor for male infertility in Chinese men.

Influences of Mo on Nitrate Reductase, Glutamine Synthetase and Nitrogen Accumulation and Utilization in Mo-Efficient and Mo-Inefficient Winter Wheat Cultivars

The objective is to study whether the accumulation and utilization of plant N are controlled by Mo status in winter wheat cultivars. Mo-efficient cultivar 97003 （eft） and Mo-inefficient cultivar 97014 （ineff） were grown in severely Mo-deficient acidic soil （Tamm-reagent-extractable Mo 0.112 mg kg^-1） with （＋Mo） and without （-Mo） the application of 0.13 mg kg^-1 Mo. The accumulation and use efficiency of plant total N were significantly higher in ＋Mo than that in -Mo and in eft than that in ineff under Mo deficiency. N use efficiency was remarkably higher in maturity but it was forwarded to jointing stage after Mo supply, thus indicating that Mo supply promoted the N use efficiency besides N uptake and eff was efficient in N uptake and utilization. The overall activity of nitrate reductase （NR, EC 1.6.6.1） was significantly higher in ＋Mo than in -Mo and ratio of ＋Mo/-Mo was even to 14.8 at filleting stage for ineff. Activity of glutamine synthetase （GS, EC 6.3.1.2） was significantly lower in ＋Mo than in -Mo. Concentration of nitrate and glutamate were also significantly lower in ＋Mo than in -Mo, thus provided evidences for enhancing N use efficiency by Mo supply. Activities of NR and GS were significantly higher and concentrations of nitrate and glutamate were significantly lower in eff than ineff under Mo deficiency, thus indicated eff was more efficient in N reduction and utilization. It is therefore concluded that Mo could promote N accumulation and utilization in winter wheat which was directly related to NR and feedback regulated by GS. Higher Mo status also results in higher accumulation and utilization of plant N in eft.

Cloning and functional characterization of two cDNAs encoding NADPH-dependent 3-ketoacyl-CoA reductased from developing cotton fibers

Genes encoding enzymes involved in biosynthesis of very long chain fatty acids were significantly up-regulatedduring early cotton fiber development. Two cDNAs, GhKCR1 and GhKCR2 encoding putative cotton 3-ketoacyl-CoAreductases that catalyze the second step in fatty acid elongation, were isolated from developing cotton fibers. GhKCR1and 2 contain open reading frames of 963 bp and 924 bp encoding proteins of 320 and 307 amino acid residues,respectively. Quantatitive RT-PCR analysis showed that both these genes were highly preferentially expressed duringthe cotton fiber elongation period with much lower levels recovered from roots, stems and leaves. GhKCR1 and 2showed 30%-32% identity to Saccharomyces cerevisiae Ybr159p at the deduced amino acid level. These cotton cDNAswere cloned and expressed in yeast haploid ybr159w? mutant that was deficient in 3-ketoacyl-CoA reductase activity.Wild-type growth rate was restored in ybr159w? cells that expressed either GhKCR1 or 2. Further analysis showed thatGhKCR1 and 2 were co-sedimented within the membranous pellet fraction after high-speed centrifugation, similar to theyeast endoplasmic reticulum marker ScKar2p. Both GhKCR(s) showed NADPH-dependent 3-ketoacyl-CoA reductaseactivity in an in vitro assay system using palmitoyl-CoA and malonyl-CoA as substrates. Our results suggest thatGhKCR1 and 2 are functional orthologues of ScYbr159p.

Effect of Nitrate on Activities and Transcript Levels of Nitrate Reductase and Glutamine Synthetase in Rice

Real-time polymerase chain reaction analysis was used to compare the effect of NO3^- on the activities of nitrate reductase （NR） and glutamine synthetase （GS）, and the transcript levels of two NR genes, OsNial and OsNia2, two cytosolic GS1 genes, OsGln1;1 and OsGln1;2, and one plastid GS2 gene OsGln2, in two rice （Oryza sativa L.） cultivars Nanguang （NG） and Yunjing （Y J）. Both cultivars achieved greater biomass and higher total N concentration when grown in a mixed N supply than in sole NH4^＋ nutrition. Supply of NO3^- increased NR activity in both leaves and roots. Expression of both NR genes was also substantially enhanced and transcript levels of OsNia2 were significantly higher than those of OsNial. NO3 also caused an increase in GS activity, but had a complex effect on the expression of the three GS genes. In roots, the OsGln1;1 transcript increased, but OsGln1;2 decreased. In leaves, NO3^- had no effect on the GS1 expression, but the transcript for OsGln2 increased both in the leaves and roots of rice with a mixed supply of N. These results suggested that the increase in GS activity might be a result of the complicated regulation of the various GS genes. In addition, the NO3-induced increase of biomass, NR activity, GS activity, and the transcript levels of NR and GS genes were proportionally higher in NG than in Y J, indicating a stronger response of NG to NO3^- nutrition than YJ.

Association Between Homocysteine Level and Methylenetetrahydrofolate Reductase Gene Polymorphisms in Type 2 Diabetes Accompanied by Dyslipidemia

Objective To investigate the association between total homocysteine(tHcy)level in plasma and methylenetetrahydrofblate reductase(MTHFR)C677T and A1298C genetic polymorphisms in a Chinese Han nationality population with type 2 diabetes mellitus(T2DM)accompanied by dyslipidemia.Methods This case-control study enrolled T2DM patients with dyslipidemia and without dyslipidemia respectively.Sanger dideoxy-mediated chain-termination method was used to detect the gene polymorphisms of MTHFR C677T and A1298C.Plasma tHcy and lipid levels were measured as well.The genotype frequency and allele frequency between the dyslipidemia and non-dyslipidemia groups were compared by using Chi-square test.Plasma tHcy level ofT2DM patients who carried the different genotypes was compared by Student's t test.Results Finally,82 T2DM patients with dyslipidemia and 94 ones without dyslipidemia were included in this study.There was a significant correlation between tHcy level and MTHFR C677T gene polymorphism inT2DM patients(t=2.27,P=0.02).Moreover,the plasma tHcy level in the dyslipidemia patients who carried MTHFR 677TT genotype was significantly higher than that in those with CT+CC genotype(13.62+6.97 vs.10.95+3.62pmol/L,t=2.2O,P=0.03);while for patients without dyslipidemia,comparison of the tHcy level between those who carried the above two alleles showed no significantly difference(13.34±6.03 vs.12.04±5.09μmol/L,t=1.08,P=0.29).Conclusion MTHFR 677TT genotype might associate with higher tHcy level in T2DM patients with dyslipidemia.

Interaction of methylenetetrahydrofolate reductase C677T,cytochrome P4502E1 polymorphism and environment factors in esophageal cancer in Kazakh population

AIM： To evaluate the association and interaction of genetic polymorphisms in methylenetetrahydrofolate reductase （MTHER） and cytochrome P4502E1 （CY- P4502E1）, environment risk factors with esophageal cancer （EC） in Kazakh, a high EC incidence area of Xinjiang Uygur Autonomous Region, China. METHODS： A 1：2 matched case-control study was conducted with 120 cases of EC and 240 populationor hospital-based controls. The controls were matched for sex, nationality, area of residence and age within a 5-year difference. MTHER and CYP4502E1 genotypes were identified by PCR-based restriction fragment length polymorphism （RFLP）. A conditional logistic regression model was established to identify risk factors. The strata method was adopted in interaction analysis. RESULTS： Low consumption of green vegetables and fresh fruits, alcohol drinking, and unsafe water （shallow well, or river） were found to be the risk factors for EC. Individuals with the MTHFR677 （C/T ＋ T/T） genotype had a 2.62-fold （95% CI： 1.61-4.28） risk of developing EC compared with those who carried the C/C genotype. Individuals with the CYP4502EIC1/C1 genotype had a 3.00-fold （95% CI： 1.82-4.96） risk compared with those who carried the CYP4502E1 （C1/C2 ＋ C2/C2） genotype. Gene-environment interaction analysis showed that MTHFR677 gene polymorphism was correlated with consumption of green vegetables and fresh fruit, while CYP4502E1 C1/C1 was correlated with alcohol drinking and unsafe drinking water. MTHFR and CYP4502E1 analysis of gene-gene interaction showed that individuals with the MTHFR677 （C/T ＋ T/T） and CYP4502EIC1/ C1 genotypes had a 7.41-fold （95% CI： 3.60-15.25） risk of developing EC compared with those who carried the MTHFR677C/C and CYP4502E1 RsaI C1/C2 ＋ C2/C2 genes, and the interaction rate was higher than that of the two factors alone. CONCLUSION： Low consumption of green vegetables and fresh fruits, alcohol drinking, and unsafe water （shallow well, or river） and polymorphisms in MTHFR and CYP4502E1 genes are important risk factors for EC. There is a synergistic interaction among polymorphisms in MTHFR and CYP4502E1 genes and environment factors. MTHFR and CYP4502E1 genes can be used as biomarkers for prevention of EC in Kazakh, Xinjiang Uygur Autonomous Region, China.

Inhibitory effect of two Indian medicinal plants on aldose reductase of rat lens in vitro

Objective:To assesse the inhibitor) effect of alcoholic extract of two Indian medicinal plants namely Ceasalpinia digyna Rottler and.Alangium lamarckii Thwaits on aldose reductase（AR） of rat lens.Methods:Rats lens were enucleated through posterior approach and their homogenate was prepared and centrifuged to obtain a clear supernatant for the determination of AR activity and protein content.Results:The alcoholic extract of Ceasalpirda digyna and Alangium lamarckii had a potent inhibitory effect on the lens AR enzyme.The IC50 values of alcoholic extract of the selected plants were calculated and were（46.29±11.17） and（106.00±5.11）μg/mL,respectively. Quercetin was used as a positive control and its IC50 value was（2.95±1.53）μg/mL.Conclusions:Thus,it is concluded that alcoholic extracts of the selected plant exhibit significant inhibitory effects on AR in the rat lens in vitro.

Methylenetetrahydrofolate reductase C677T and A1298C polymorphisms and gastric cancer susceptibility

AIM: To identify the association between methylenetetrahydrofolate reductase (MTHFR) polymorphisms and gastric cancer (GC) susceptibility.

Changes of Nitrate Reductase Activity in Cucumber Seedlings in Response to Nitrate Stress

In China, nitrogen fertilizer application rates in intensive agricultural systems have increased dramatically in recent years, especially in protected vegetable production systems. This excessive use of nitrogen fertilizer has resulted in soil secondary salinization, which has become a significant environmental stress for crops such as cucumber, in the protected farmland of China. So it is necessary to illuminate how crops respond to nitrate stress. The objective of this work was to examine the effects of increased nitrate concentration [14 （CK） and 140 mmol L^-1 （T）] on NO3- concentration, and in vitro and in vivo nitrate reductase activities in the roots and leaves of cucumber （Cucumis sativus L. cv. Xintaimici） seedlings with hydroponic culture. The results showed that the NO3- concentration in the roots and leaves of T seedlings significantly increased over treatment course, and at 12 d increased by 1.08 and 1.72 times with respect to CK seedlings, respectively; in vitro nitrate reductase activity of T was increased dramatically to 1.74 times of CK in the roots at 2 d and 1.56 times of CK in the leaves at 6 d, and then decreased. At 12 d, in vitro activity was still 24.3% higher in the roots and only 9.9% lower in the leaves than CK. Compared with in vitro nitrate reductase activity, in vivo activity responded differently to the increase of treatment time. At the beginning, in vivo nitrate reductase activity in the roots and leaves of T had no significant difference from CK, whereas with the increase of treatment duration, the activity decreased. At 12 d, in vivo activity in the roots and leaves of T lowered by 20.1 and 52.8% with respect to CK, respectively. This evidence suggests that posttranslational activation of nitrate reductase in cucumber seedlings may be seriously inhibited by nitrate stress.