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N Dai

Publications and source records attributed to N Dai.

At least 19 recordsLinked to original sources
PubMed2006

Effects of cytokinin production under two SAG promoters on senescence and development of tomato plants.

Two promoters of senescence-associated ARABIDOPSIS genes, SAG12 and SAG13, were used in tomato plants to express IPT that catalyzes the rate-limiting step in cytokinin biosynthesis. Expression of these heterologous promoters in tomato plants was analyzed using the reporter gene beta-glucuronidase. Both promoters are expressed in tomato leaves in a manner similar to their expression in ARABIDOPSIS plants. The SAG12 promoter is very specific to senescing leaves, whereas the SAG13 promoter is expressed in mature leaves prior to the onset of visible senescence and its expression increases in senescing leaves. Expression of both promoters in tomato tissues other than leaves was very low . IPT expressed under the control of SAG12 and SAG13 promoters ( PSAG12::IPT and PSAG13::IPT, respectively) resulted in suppression of leaf senescence and advanced flowering, as well as in a slight increase in fruit weight and fruit total soluble solids (TSS). However, expression of PSAG13::IPT also led to stem thickening, short internodal distances and loss of apical dominance. In contrast to the autoregulation of PSAG12::IPT, PSAG13::IPT is expressed at higher levels in mature leaves. This difference is likely due to PSAG13::IPT exhibiting two phases of expression - a senescence-independent expression prior to the onset of senescence that is not subjected to autoregulation by cytokinin, and enhanced expression throughout senescence which is autoregualted by cytokinin. This moderate different autoregulated behavior of PSAG12::IPT and PSAG13::IPT markedly influenced plant development, emphasizing the biological effects of cytokinin in addition to senescence inhibition.

Alcohol Oxidoreductases↗
PubMed2006

Little Egrets (Egretta garzetta) and trace-metal contamination in wetlands of China.

The rapidly developing Asian countries may face threatening environmental contamination, that however remains largely unassessed. We studied persistent trace elements in three wetlands, Poyang Lake, relatively unpolluted, and Tai Lake, and Pearl River Delta, selected as hotspots of pollution in Central China. We adopted as indicator the Little Egret, a widespread colonial waterbird, and during 1999 and 2000 we collected and analysed the same samples as for a parallel study we conducted in Pakistan, e.g. eggs, body feathers of chicks, prey spontaneously regurgitated by the chicks, and sediments at the areas most used by foraging egrets. The levels of trace-metals at our three study areas were similar, or within the range, of those found in the few other studies for East Asia, with few exceptions. The concentrations of the various elements were below the threshold that may affect the survival or reproduction of the birds, and even the highest concentrations relative to background, i.e. Se in eggs, and Hg in feathers at Pearl Delta, do not pose toxic hazards. In sediments, the levels of trace elements were lower than the critical levels assumed for contaminated soil, except for alarming high levels of As at Poyang. These results do not confirm our expectation, that Poyang was relatively uncontaminated, while Tai and Pearl were polluted. Although trace metal concentration differed significantly among the three study areas, these differences were minor and were not consistent among elements and samples. The bioaccumulation ratios from sediments through prey, feather and egg, were consistent with our previous findings for Pakistan. Only Hg exhibited high bioaccumulation, while Se and Zn had low accumulation, and the other elements no accumulation. This reasserts that feathers of predators such as egrets, may be more sensitive indicators of environmental contamination for the elements subject to bioaccumulation, whereas the sediments or the organisms low in the food chain are better indicators for the other elements.

Animals↗
PubMed2002

Complete mitochondrial genomes confirm the distinctiveness of the horse-dog and sheep-dog strains of Echinococcus granulosus.

Unlike other members of the genus, Echinococcus granulosus is known to exhibit considerable levels of variation in biology, physiology and molecular genetics. Indeed, some of the taxa regarded as 'genotypes' within E. granulosus might be sufficiently distinct as to merit specific status. Here, complete mitochondrial genomes are presented of 2 genotypes of E. granulosus (G1-sheep-dog strain: G4-horse-dog strain) and of another taeniid cestode, Taenia crassiceps. These genomes are characterized and compared with those of Echinococcus multilocularis and Hymenolepis diminuta. Genomes of all the species are very similar in structure, length and base-composition. Pairwise comparisons of concatenated protein-coding genes indicate that the G1 and G4 genotypes of E. granulosus are almost as distant from each other as each is from a distinct species, E. multilocularis. Sequences for the variable genes atp6 and nad3 were obtained from additional genotypes of E. granulosus, from E. vogeli and E. oligarthrus. Again, pairwise comparisons showed the distinctiveness of the G1 and G4 genotypes. Phylogenetic analyses of concatenated atp6, nad1 (partial) and cox1 (partial) genes from E. multilocularis, E. vogeli, E. oligarthrus, 5 genotypes of E. granulosus, and using T. crassiceps as an outgroup, yielded the same results. We conclude that the sheep-dog and horse-dog strains of E. granulosus should be regarded as distinct at the specific level.

Amino Acid Sequence↗
PubMed2001

Cloning and characterization of a cDNA encoding hexokinase from tomato.

Two different partial sequences encoding putative hexokinase (HXK, ATP: hexose-6-phosphotransferase, EC 2.7.1.1) were isolated from tomato (Lycopersicon esculentum) by RT-PCR using degenerate primers. Southern blot analysis suggested the existence of two divergent HXK genes. A complete cDNA of one HXK was isolated by screening a cDNA library prepared from young cherry tomato fruit. The 1770 bp cDNA of LeHXK2 contained an open reading frame encoding a 496 amino acid protein that has 69% identity with the two Arabidopsis HXKs, 83 and 85% identity with potato StHXK1 and tobacco NtHXK, respectively. However, this clone had 97% amino acid identity with potato StHXK2 and, therefore, was named LeHXK2. LeHXK2 cDNA was expressed in a triple mutant yeast (Saccharomyces cerevisiae) strain which lacked the ability to phosphorylate glucose and fructose and, therefore, was unable to grow on these sugars as carbon sources. Mutant cells expressing LeHXK2 grew on both glucose and fructose with shorter doubling time on glucose. The kinetic properties of LeHXK2 expressed in yeast were determined after the purification of LeHXK2 by HPLC-ion exchange chromatography, confirming the identity of LeHXK2 as hexokinase with higher affinity to glucose. LeHXK2 mRNA was detected by RT-PCR expression analysis in all organs and tissues and at all stages of fruit development. However, semi-quantitative RT-PCR analysis showed that LeHXK2 was most highly expressed in flowers.

Journal Article↗
PubMed2001

Characterization of native and yeast-expressed tomato fruit fructokinase enzymes.

Three fructokinase isozymes (FKI, FKII, FKIII) were separated from both immature and ripe tomato fruit pericarp. All three isozymes were specific for fructose with undetectable activity towards glucose or mannose. The three isozymes could be distinguished from one another with respect to response to fructose, Mg and nucleotide donor concentrations and this allowed the comparison of the fruit enzymes with the gene products of the two known cloned tomato fructokinase genes, LeFRK1 and LeFRK2. FKI was characterized by both substrate (fructose), as well as Mg, inhibition; FKII was inhibited by neither fructose nor Mg; and FKIII was inhibited by fructose but not by Mg. ATP was the preferred nucleotide donor for all three FKs and FKI showed inhibition by CTP and GTP above 1 mM. All three FKs showed competitive inhibition by ADP. During the maturation of the tomato fruit total FK activity decreased dramatically. There were decreases in activity of all three FKs, nevertheless, all were still observed in the ripe fruit. The two tomato LeFRK genes were expressed in yeast and the gene products were characterized with respect to the distinguishing characteristics of fructose, Mg and nucleotide inhibition. Our results indicate that FKI is the gene product of LeFRK2 and FKII is probably the gene product of LeFRK1.

Chromatography, High Pressure Liquid↗
PubMed2001

[The effect of epidermal growth factor on the pathologic changes of gastric mucosa in SD rats with chronic atrophic gastritis].

OBJECTIVE: To study the effect of epidermal growth factor (EGF) on the pathologic changes of gastric mucosa in rats with chronic atrophic gastritis(CAG). METHODS: The established rat models of CAG were divided into therapy group and control group. The rats in the therapy group received EGF 10 microg/kg subcutaneously (SC), whereas these in the control group the same volume of normal saline SC. 12 weeks later, all rats were killed by cervical dislocation and their gastric mucosa were examined with microscope. RESULTS: The grade of inflammatory cell infiltration in the therapy group was lower than that in the control group (P < 0.01). The thickness of gastric mucosal gland layer was (215.0 +/- 20.7) microm in the therapy group and (139.2 +/- 13.8) microm in the control group (P < 0.01). The ratio of the thickness of gastric mucosal glands and muscularis mucosa(L(1)/L(2)) was 2.70 +/- 0.34 in the therapy group and 1.27 +/- 0.27 in the control group (P < 0.01). The number of gastric glands in 1 mm length of mucosal layer was 26.20 +/- 1.27 in the therapy group and 19.90 +/- 1.78 in the control group (P < 0.01). In the therapy group, the gastric glands were rearranged in order, without signs of malignant proliferation. The width of the expression of proliferating cell nuclear antigen (PCNA ) of gastric mucosa was higher in the therapy group than in the control group [(77.70 +/- 4.16) microm vs (54.40 +/- 4.54) microm, P < 0.01]. CONCLUSIONS: EGF played a therapeutic role in reversing the gastric mucosal atrophy of the rats with CAG. It promoted the expression of PCNA, which induced a protective proliferation of the gastric mucosal lesions in the rats with CAG.

Animals↗
PubMed2000

[Experimental study on inhibitory effect of Chinese herbal compound on hepatocyte cytochrome P450 II E1 expression in rat model of nonalcoholic fatty liver].

OBJECTIVE: To study the effect of Chinese herbal compound (CHC) on hepatocyte cytochrome P450 II E1 expression in rat model of nonalcoholic fatty liver (NFL). METHODS: CHC was given to the models of NFL formed by high fat diet, and changes on pathology of liver and hepatocyte cytochrome P450 II E1 expression, as well as the contents of malonyldialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), vitamin E (VitE) and triglyceride (TG) in liver were observed and compared with those in the control group. RESULTS: The fatty degeneration of liver recovered to normal basically in the CHC group. Immunohistochemical examination showed that CHC could inhibit the hepatocyte cytochrome P450 II E1 expression markedly, and restore the liver contents of MDA, SOD, GSH, VitE and TG to near normal range. CONCLUSION: CHC could inhibit the hepatocyte cytochrome P450 II E1 expression markedly in rats with fatty liver, therefore, has the effect of preventing fatty liver.

Animals↗
PubMed1999

Overexpression of Arabidopsis hexokinase in tomato plants inhibits growth, reduces photosynthesis, and induces rapid senescence.

Sugars are key regulatory molecules that affect diverse processes in higher plants. Hexokinase is the first enzyme in hexose metabolism and may be a sugar sensor that mediates sugar regulation. We present evidence that hexokinase is involved in sensing endogenous levels of sugars in photosynthetic tissues and that it participates in the regulation of senescence, photosynthesis, and growth in seedlings as well as in mature plants. Transgenic tomato plants overexpressing the Arabidopsis hexokinase-encoding gene AtHXK1 were produced. Independent transgenic plants carrying single copies of AtHXK1 were characterized by growth inhibition, the degree of which was found to correlate directly to the expression and activity of AtHXK1. Reciprocal grafting experiments suggested that the inhibitory effect occurred when AtHXK1 was expressed in photosynthetic tissues. Accordingly, plants with increased AtHXK1 activity had reduced chlorophyll content in their leaves, reduced photosynthesis rates, and reduced photochemical quantum efficiency of photosystem II reaction centers compared with plants without increased AtHXK1 activity. In addition, the transgenic plants underwent rapid senescence, suggesting that hexokinase is also involved in senescence regulation. Fruit weight, starch content in young fruits, and total soluble solids in mature fruits were also reduced in the transgenic plants. The results indicate that endogenous hexokinase activity is not rate limiting for growth; rather, they support the role of hexokinase as a regulatory enzyme in photosynthetic tissues, in which it regulates photosynthesis, growth, and senescence.

Arabidopsis↗
PubMed1999

[Correlation between hepatocyte cytochrome P450IIE1 expression and oxidation, antioxidation in rat nonalcoholic steatosis model].

OBJECTIVE: To study the correlation between hepatocyte cytochrome P450 II E1(CYP II E1) expression and oxidation, antioxidation in rat nonalcoholic steatosis model. METHODS: The expression of hepatocyte CYP II E1 antigen in rat steatosis model induced by high fat diet was detected with immnohistochemistry. Meanwhile, MDA, SOD, GSH and VitE contents in the liver were measured by biochemical analysis. RESULTS: Expression of CYP II E1 in rat nonalcoholic steatosis by high fat diet was prominent in hepatic acinar zone 3, and had a more extensive acinar distribution from zone 3 to zone 2, MDA contents in fatty liver was significantly increased than in normal, SOD, GSH and VitE contents were significantly decreased than in normal. There were significant positive correlation between CYP II E1 and MDA (P < 0.01), and negative correlation between CYP II E1 and SOD, GSH, VitE (P < 0.05, P < 0.05, P < 0.01). CONCLUSIONS: Hepatocyte CYP II E1 expression in nonalcoholic steatosis is prominent in hepatic acinar zone 3. Its expression resembles alcoholic fatty liver. There is significant correlation between CYP II E1 and lipid peroxidation.

Animals↗
PubMed1999

[Intercellular adhesion molecule-1 expression in experimental liver fibrosis].

OBJECTIVE: To explore the role of intercellular adhesion molecule-1 (ICAM-1) in experimental liver fibrosis. METHODS: Experimental liver fibrosis models of rats were induced by high fat diet, low fat diet plus ethanol, high fat diet plus ethanol, and carbon tetrachloride subcutaneous injection respectively. At sacrifice, liver pathologic changes were studied and ICAM-1 expression was evaluated with immunohistochemistry by using a monoclonal antibody. RESULTS: ICAM-1 expression was observed in the hepatocellular membrane; ICAM-1 positive hepatocytes were localized in zones of portal tract with focal necrosis and inflammatory damage. Staining for ICAM-1 was associated with the degree of liver inflammation and fibrosis. In the different models, the intensity of ICAM-1 expression was different; It ranged in an increasing order from high fat diet, low fat diet plus ethanol, high fat diet plus ethanol, and carbon tetrachloride model. The strongest reactivity for ICAM-1 was seen in carbon tetrachloride model (P < 0.05), the difference was significant as compared with the other models. However, there was no significant difference among the three other models (P > 0.05). CONCLUSION: Upregulation of ICAM-1 expression in experimental liver fibrosis may be related with liver fibrogenesis.

Animals↗
PubMed1999

[Effects of Kupffer cells stimulated by triglyceride and very low-density lipoprotein on proliferation of rat hepatic stellate cells].

OBJECTIVE: To study the effects of Kupffer cell-conditioned medium (KCCM) derived from triglyceride and very low-density lipoprotein (VLDL) treatment on proliferation of rat hepatic stellate cells (HSC). METHODS: HSC and Kupffer cells were isolated from liver of Wistar rats by in situ perfusion with pronase and collagenase and density gradient centrifugation with Nycodenz and then cultured. KCCM was prepared and MTT colorimetric assay was used to detect HSC proliferation. RESULTS: HSC and Kupffer cells were isolated successfully with high purity. 12.5 mg/L of triglyceride and 25 - 100 mg/L of VLDL promoted HSC proliferation (P < 0.05 or 0.01); KCCM + triglyceride and KCCM + VLDL might promote HSC proliferation as compared with a control group (P < 0.01). There was no significant difference between KCCM + triglyceride and KCCM + VLDL (P > 0.05). CONCLUSION: The technique for isolation of HSC and Kupffer cells described here is simple and reliable. Triglyceride, VLDL and KCCM stimulated by them may promote HSC proliferation and be associated with fatty liver and hepatic fibrogenesis.

Animals↗
PubMed1998

Tomato fructokinases exhibit differential expression and substrate regulation

Two divergent genes encoding fructokinase, Frk1 and Frk2, have been previously shown to be expressed in tomato (Lycopersicon esculentum L.) and have now been further characterized with regard to their spatial expression and the enzymic properties of the encoded proteins. Frk1 and Frk2 mRNA levels were coordinately induced by exogenous sugar, indicating that both belong to the growing class of sugar-regulated genes. However, in situ hybridization indicated that Frk1 and Frk2 were expressed in a spatially distinct manner, with Frk2 mRNA primarily localized in cells of the fruit pericarp, which store starch, and Frk1 mRNA distributed ubiquitously in pericarp tissue. To evaluate the biochemical characteristics of the products of the Frk1 and Frk2 genes, each cDNA was expressed in a mutant yeast (Saccharomyces cerevisiae) line defective in hexose phosphorylation and unable to grow on glucose or fructose (Fru). Both Frk1 and Frk2 proteins expressed in yeast conferred the ability to grow on Fru and exhibited fructokinase activity in vitro. Although both Frk1 and Frk2 both utilized Fru as a substrate, only Frk2 activity was inhibited at high Fru concentrations. These results indicate that Frk2 can be distinguished from Frk1 by its sensitivity to substrate inhibition and by its temporal and spatial pattern of expression, which suggests that it plays a primary role in plant cells specialized for starch storage.

Journal Article↗
PubMed1997

Sugar induced cell death in yeast is dependent on the rate of sugar phosphorylation as determined by Arabidopsis thaliana hexokinase.

Sugars like glucose and fructose induce death of yeast cells within a few hours, in the absence of additional nutrients to support growth, while cells incubated in water remain viable for weeks. This sugar-induced cell death (SICD) by glucose and fructose required glucose or fructose phosphorylation since yeast cells deficient in hexose phosphorylation did not die. However, when hexose phosphorylation is restored by complementation with Arabidopsis thaliana hexokinase, the cells died. The affinity of A. thaliana hexokinase is about 400 times higher for glucose than for fructose, therefore, A. thaliana hexokinase was further utilized to study the role of hexose phosphorylation in SICD. The rate of SICD of hexokinase-deficient yeast cells expressing A. thaliana hexokinase was significantly slower in fructose than in glucose, indicating that SICD is determined by the rate of hexose phosphorylation. The significance of hexose phosphorylation and its role in SICD is discussed.

Journal Article↗
PubMed1997

Divergent fructokinase genes are differentially expressed in tomato.

Two cDNA clones (Frk1 and Frk2) encoding fructokinase (EC 2.7.1.4) were isolated from tomato (Lycopersicon esculentum). The Frk2 cDNA encoded a deduced protein of 328 amino acids that was more than 90% identical with a previously characterized potato (Solanum tuberosum) fructokinase. In contrast, the Frk1 cDNA encoded a deduced protein of 347 amino acids that shared only 55% amino acid identity with Frk2. Both deduced proteins possessed and ATP-binding motif and putative substrate recognition site sequences identified in bacterial fructokinases. The Frk1 cDNA was expressed in a mutant yeast (Saccharomyces cerevisiae) line, which lacks the ability to phosphorylate glucose and fructose and is unable to grow on glucose or fructose. Mutant cells expressing Frk1 were complemented to grow on fructose but not glucose, indicating that Frk1 phosphorylates fructose but not glucose, and this activity was verified in extracts of transformed yeast. The mRNA corresponding to Frk2 accumulated to high levels in young, developing tomato fruit, whereas the Frk1 mRNA accumulated to higher levels late in fruit development. The results indicate that fructokinase in tomato is encoded by two divergent genes, which exhibit a differential pattern of expression during fruit development.

Amino Acid Sequence↗
PubMed1997

[Experimental study on effect of bushen shengjing decoction on kidney yang and testicular dysfunction in rats].

OBJECTIVE: To explore the therapeutical mechanism of Bushen Shengjing Decoction (BSSJD) in treating infertility. METHODS: Fed Wistar male rats with adenine 30 mg/100 g.d continuously for 30 days. The rats manifested the symptom which was similar to the human Kidney Yang Deficiency, the genitality dropped, the function of sperm-producing in the testis was disturbed, the contents of luteinizing hormone (LH), testosterone (T) and compound F (F) in blood were all lower than rats of normal group, P < 0.01. The model rats took the BSSJD 3 ml/100 g.d (each ml contains crude drugs 2 g) continuously for 10 days, interval for three days, then medicated again and total medication of BSSJD was 30 days. RESULTS: The symptom of Kidney Yang Deficiency in rats was improved obviously, the genitality, sperm quality and function of sperm producing in testis were all enhanced obviously, so did the hormone level of LH, T, F in blood. Comparing to untreated control group, the difference was significant (P < 0.05). CONCLUSION: BSSJD has the function of reinforcing Yang and replenishing essence and regulate the endocrinological function.

Adenine↗
PubMed1996

The 5' untranslated region of Arabidopsis thaliana calmodulin cDNA is an independent cDNA containing an open reading frame.

A cDNA clone, pAUK1, with an open reading frame (ORF) coding for a hypothetical 164-amino-acid protein was isolated from an Arabidopsis thaliana (L.) Heynh cDNA library. The clone was attached, tail to tail, to the 3' end of A. thaliana hexokinase cDNA. An almost identical sequence had been previously described as the 5' untranslated region (5' UTR) of A. thaliana calmodulin cDNA (ACaM-2). Sequence comparison with three additional A. thaliana truncated cDNA clones which appear in a database (GenBank) supports the conclusion that pAUK1 is identical to the 5' UTR of ACaM-2 and that the 5' UTR of ACaM-2 is an independent cDNA artificially linked to A. thaliana calmodulin cDNA.

Amino Acid Sequence↗