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Kun Xu

Publications and source records attributed to Kun Xu.

16 recordsLinked to original sources
PubMed2006

Theoretical study on the kinetics and mechanism for the reaction of FCO with NO.

The radical reaction mechanism of FCO + NO on the ground electronic state energy surface has been studied at the G2M level of theory based on the geometric parameters optimized at the B3LYP/6-311+G(d) level of theory. The two kinds of reaction pathways include the direct fluorine abstraction channel producing CO + FNO and the association channel forming the FC(O)NO complex. The former has a distinct barrier of 8.9 kcal mol(-1), while the latter is a barrierless association process. The rate constant of this reaction system in the temperature range 200-3000 K has been calculated by the microcanonical VTST/RRKM theory. The theoretical result shows that the predicted total rate constants exhibit a negative-temperature dependence and positive-pressure effect at lower temperatures. Under the experimental conditions, the predicted values are in good agreement with the experimental results. In addition, the predicted branching ratios clearly indicate that the dominant product channel is the formation of FC(O)NO at low temperatures and FNO + CO at high temperatures (>500 K).

Journal Article↗
PubMed2006

Flexible and reversible responses to different irradiance levels during photosynthetic acclimation of Cypripedium guttatum.

Cypripedium guttatum can be found both in open and shady habitats. Photosynthetic acclimation of C. guttatum to different light availabilities was detected using measurements of chlorophyll fluorescence, photosynthesis and leaf traits. When growing under low light conditions, C. guttatum exhibited a greater efficiency in photochemical utilization of absorbed light energy, and a lower ability for non-photochemical dissipation of excess light energy, as compared to the plants growing under high light conditions. Under intermediate light conditions, C. guttatum exhibited higher photosynthetic capacity (A(max)) than those under both low light or high light conditions. The differences in A(max) among three light environments was linked to the differences in biochemical efficiency, leaf N content (LNC) and leaf dry mass per unit area (LMA), but not to the differences of chlorophyll content. However, there were no significant differences in the light compensation points (LCP) and light saturation points (LSP) for photosynthesis for the plants growing under the three light conditions. These results indicate that the photosynthetic capacity of C. guttatum leaves allows for flexible and reversible responses to different irradiance levels. Photosynthetic acclimation in C. guttatum was affected by biochemical changes, the changes in LMA and ratio of Chl a/b. Successful acclimation of C. guttatum to a broad range of light levels likely allows for its wide geographical distribution. A level of about 45% sunlight appears to be optimal for photosynthesis.

Acclimatization↗
PubMed2006

[Responses of grafted eggplant seedling roots to low temperature stress].

The study on the changes of physiological and biochemical properties of grafted eggplant seedling roots under low temperature stress and the relationships between these changes and cold tolerance showed that at the initial stage of treating with 10 degrees C (daytime) /3 degrees C (night), eggplant seedling roots were most impressible to low temperature, with the MDA content, chilling injury index, POD activity, proline content and soluble protein content increased significantly, and root respiration rate, SOD activity and CAT activity decreased rapidly. With the extending of low temperature stress, root respiration rate and osmotic adjustment reduced continually, while chilling injury index increased. After 3 days recovery, the respiration rate, osmotic adjustment and SOD activity were increased. Among the test materials, T2 (with Hiranasu as rootstock) had the best recovery capability, followed by T1 (with Taibyo as rootstock) and CK (Jinong 2000). Grafting with stronger cold tolerance rootstock could improve eggplant root activity, and thus, its cold resistance markedly.

Catalase↗
PubMed2006

[Molecular mapping of the gene(s) controlling petal-loss trait in Brassica napus].

An F2 population derived from a cross between apetalous line' APT02 'and normal petalled cultivar 'ZS NO.4' was used for molecular marker searching and chromosomal mapping of the gene(s) controlling petal-loss trait in Brassica napus. Twenty pairs of AFLP primers and 170 pairs of SRAP primers were selected and screened from two parents. In further selection through bulked segregant analysis (BSA) approach, one SRAP marker e8m3_4 (600 bp) and one AFLP marker E3247_15 (150 bp) were obtained and found to be linked to the gene(s) controlling petal-loss trait, with the genetic distance of 5 cM and 13.5 cM. A linkage map in Brassica napus was constructed. It consisted of 213 AFLP56 SSR loci and a morphology marker throughout 17 main linkage groups, two triplet and four linkage pairs. Total length of the map covered 2,487.1 cM, and average interval between markers was 10.09 cM. By genetic mapping, the gene(s) controlling petal-loss trait (WHB)was mapped in LG4.

Amplified Fragment Length Polymorphism Analysis↗
PubMed2006

[Cold tolerance and wintering cultivation effect of different Welsh onion varieties].

With Welsh onion Zhangqiu as the contrast, this paper measured the physiological indices including electrolyte leakage, malondialdehyde content, protective enzyme activity, chlorophyll content, photosynthetic rate and root vitality of two introduced Welsh onion varieties Chunwei and Changhao, and identified their cold tolerance and wintering cultivation effect. The results showed that during wintering cultivation, all test Welsh onion varieties suffered low temperature stress, which led the electrolyte leakage and malondialdehyde content arrived at the maximum, while the chlorophyll content and photosynthetic rate dropped to the bottom at 15 January. At this time, the function data of physiological indices were 0. 452, 0. 364, and 0. 226 for Chuowei, Changbao and Zhangqiu, respectively, suggesting that Chunwei had stronger cold tolerance, followed by Changbao, and Zhangqiu. The bolting rate of Chunwei, Changbao and Zhangqiu when harvested was 0, 35.2% and 81.0% , respectively. Although the biological yield of Changbao was 25.67% and 52. 94% higher than that of Chunwei and Zhangqiu, respectively, the economic yield of Chunwei was the highest (5.49 kg m2) , with an increment of 18. 57% than Changbao, and that of Zhangqiu was only 0. 86 kg x m(-2) It could be concluded that Chonwei was fit to cultivate in low tunnel in winter, while Zhangqiu was weaker in cold tolerance and not fit to wintering cultivation.

Allium↗
PubMed2005

Multiple translational temperature model and its shock structure solution.

Within a shock layer, the translational motion of the gas is more energetic in the direction perpendicular to the shock front than in the direction parallel to the shock. To predict this translational nonequilibrium, a generalized gas-kinetic BGK model is proposed. With the adaptation of a continuum gas distribution function truncated up to the Navier-Stokes order and a generalized particle collision time, this newly constructed kinetic model is used in the monatomic gas shock structure calculations, where two translational temperatures inside the shock layer are well captured.

Journal Article↗
PubMed2005

Photosynthesis in relation to reproductive success of Cypripedium flavum.

BACKGROUND AND AIMS: Cypripedium flavum is a rare, endemic alpine slipper orchid of China, which is under threat from excessive collection and habitat changes. Conservation and re-introduction of C. flavum is restricted by lack of knowledge of the plant's photosynthesis and how that affects reproductive success. The hypothesis is tested that reproductive success is determined by photosynthetic production. * METHODS: To understand the photosynthetic characteristics and adaptation of C. flavum to alpine environments, and the relation to reproductive success, measurements were made at four field sites with varying degrees of forest cover in the Hengduan Mountains, south-west China. * KEY RESULTS: Both photosynthetic capacity and reproductive traits of C. flavum are affected by light availability. Photosynthetic rate (A) is greatest around noon, following the pattern of photosynthetically active radiation (PAR) at all sites. Cypripedium flavum has highest daily mean photosynthetic rate (A(daily)) and light-saturated photosynthetic rate (A(max)) under a half to a third of full sunlight. High radiation decreased A. However, the optimum temperature for photosynthesis was similar (18-20 degrees C) at all sites. * CONCLUSIONS: The quotient of daily mean photosynthetic rate to light saturated photosynthesis (A(daily)/A(max)) is positively correlated with the ramet number m(-2) and percentage of fruiting of C. flavum. The A(daily)/A(max) ratio is a useful proxy for evaluating reproductive success of C. flavum.

Carbon Dioxide↗
PubMed2005

[Effects of Meloidogyne incognita initial inoculation density on ginger growth].

The study with potted ginger showed that Meloidogyne incognita infection could reduce the plant height, stem diameter, quantity of shoots, and fresh weight of stem, leaf and root, and finally, reduce ginger yield. With the enhancement of M. incognita initial inoculation density, the growth of ginger was damaged more severely, e. g., under inoculating 50, 100 and 200 M. incognita eggs per 100 g soil, ginger yield decreased by 27.91%, 37.73% and 42.14%, respectively. The reproduction rate of M. incognita was also affected by the initial inoculation density, the lower the initial inoculation density, the higher the reproduction rate. When the inoculation density reached 746.20 eggs per 100 g soil, the reproduction rate was 1.

Animals↗
PubMed2004

[Study on nerve growth factor liposomes on crossing blood-brain barrier in vitro and in vivo].

AIM: To study the permeability of nerve growth factor (NGF) liposomes (NGF-L, NGF-SSL, NGF-SSL-T) on the blood-brain barrier (BBB) model and the distribution in vivo, and analyze the correlation between the results in vitro and in vivo. METHODS: The BBB model in vitro was established by using mouse brain microvascullar endothelial cell, and the model was applied to study the permeability of NGF liposomes. The distribution of NGF of each group was studied by 125I labeled and SDS-PAGE method. RESULTS: The highest encapsulation proportion was 34%, and the mean size of NGF liposomes was below 100 nm. The permeability of NGF liposomes on in vitro BBB model showed that the liposome could promote NGF to transport across the BBB, the permeability of NGF-SSL-T was the highest. The distribution in the brain showed in an order of NGF concentration NGF-SSL-T > NGF-SSL + RMP-7 > NGF-SSL > NGF-L. There was a close relationship between P(e) (permeability coefficient on in vitro BBB model) and BUI (brain uptake constant in vivo). CONCLUSION: Liposomes can promote NGF to transport across the BBB, and the transporting ability BBB of NGF-SSL-T which RMP-7 incorporated into the surface of NGF liposomes is the best.

Animals↗
PubMed2003

Measurement of hemoglobin in long-term fixed erythroid cells: application development for cell science experiments in microgravity.

Studying the effects of microgravity on cell differentiation will enhance our understanding of fundamental biology and is indispensable for a sustained space program. Rauscher murine erythroleukemic cells were chosen as a model system to study erythroid cell differentiation aboard the International Space Station because these cells undergo differentiation in response to the natural inducer, erythropoietin, as well as various chemical-inducers. We have now developed a method to quantify hemoglobin in Rauscher cells after weeks of fixation and storage required for such space biology experiments. By exploiting the pseudoperoxidase activity of hemoglobin and by using reagents that yield a soluble chromophore that freely passes out of fixed cells, we developed a highly specific and sensitive assay applicable to cells fixed as long as 4 months.

Animals↗
PubMed2003

[Effects of soil water stress and shading on growth characteristics of ginger].

Water stress decreased the chlorophyll contents, stomatic density, and stomatic size of ginger leaves, and reduced the root activity and magnitude of bleeding sap of ginger roots. Under the same water contents, shading increased the root activity and the chlorophyll contents and stomatic size of upper cuticulae of ginger leaves, but decreased the stomatic density and size of their lower cuticulae. Water stress influenced the growth and yield of ginger significantly, but the effects of light intensity on ginger growth and yield were different under different water contents. Under normal water content, ginger grew better and yield was higher in natural sunlight, while under water stress, ginger grew better and yield was higher in shading.

Chlorophyll↗
PubMed2003

[Effect of RMP-7 and its derivatives on the transportation of liposome into the brain].

AIM: To study the action of RMP-7 and its derivative on transporting liposome across the blood brain barrier (BBB) into the brain. METHODS: RMP-7 and DSPE-PEG-NHS [[1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-n-[poly (ethylene-glycol)]-hydroxy succinamide]] were conjugated together in mild condition and MALDI-TOF-MS (Matrix-Assisted Laser Desorption-Ionization Time-of-Flight Mass Spectrometry) was used to determine their molecular ratio. An in vitro BBB model was established and used to determine in vitro bioactivity of RMP-7 and its derivative. The fluorescence of brain slices and the Evens Blue (EB) concentration in the brain, liver, spleen, lung and kidney of each group were used to evaluate the in vivo bioactivity of RMP-7 and its derivative on transporting liposome across the BBB. RESULTS: The average molecular weight (MW) of the reaction product was 4,900, while those of DSPE-PEG-NHS and RMP-7 were 3,224 and 1,098. The results demonstrated that RMP-7 was conjugated to DSPE-PEG-NHS at the molecular ratio of 1:1, so the product was DSPE-PEG-RMP-7. RMP-7 and DSPE-PEG-RMP-7 was shown to improve the transporting of peralcohol enzyme across the in vitro BBB model 2-3 times higher than the peralcohol enzyme only. DSPE-PEG-RMP-7 could facilitate the transporting of EB into brain more easily than RMP-7. CONCLUSION: Both RMP-7 and DSPE-PEG-RMP-7 could facilitate the transporting of liposome across the BBB, especially DSPE-PEG-RMP-7.

Animals↗
PubMed2002

The yields, branching ratios and angular distributions of 6-7 MeV photons produced in the 19F(p,alphagamma)16O reaction.

The yields and branching ratios of 6.13, 6.92 and 7.12 MeV photons produced in the 19F(p,álphagamma)16O reaction were measured for incident proton energies between 340.46 and 3490 keV. The experimental data were recorded and analysed to show photon features. The branching ratios of 6.13, 6.92 and 7.12 MeV gamma-rays are different for different incident proton energies. The maximum yield of 6-7 MeV gamma-rays was found at Ep = 2.63 MeV. The angular distributions for 6.13 and 7.12 MeV gamma-rays in the Ep = 340.46 keV resonance were also measured and show to be isotropic within experimental uncertainty.

Journal Article↗
PubMed2001

EUDOC: a computer program for identification of drug interaction sites in macromolecules and drug leads from chemical databases.

The completion of the Human Genome Project, the growing effort on proteomics, and the Structural Genomics Initiative have recently intensified the attention being paid to reliable computer docking programs able to identify molecules that can affect the function of a macromolecule through molecular complexation. We report herein an automated computer docking program, EUDOC, for prediction of ligand-receptor complexes from 3D receptor structures, including metalloproteins, and for identification of a subset enriched in drug leads from chemical databases. This program was evaluated from the standpoints of force field and sampling issues using 154 experimentally determined ligand-receptor complexes and four "real-life" applications of the EUDOC program. The results provide evidence for the reliability and accuracy of the EUDOC program. In addition, key principles underlying molecular recognition, and the effects of structural water molecules in the active site and different atomic charge models on docking results are discussed. Copyright 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1750-1771, 2001

Journal Article↗