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排序方式: 共有47条查询结果,搜索用时 15 毫秒
1.
Reglucosylation of the Benzoxazinoid DIMBOA with Inversion of Stereochemical Configuration is a Detoxification Strategy in Lepidopteran Herbivores 总被引:1,自引:0,他引:1
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Felipe C. Wouters Dr. Michael Reichelt Dr. Gaétan Glauser Eugen Bauer Dr. Matthias Erb Prof. Jonathan Gershenzon Dr. Daniel G. Vassão 《Angewandte Chemie (International ed. in English)》2014,53(42):11320-11324
Benzoxazinoids are chemical defenses against herbivores and are produced by many members of the grass family. These compounds are stored as stable glucosides in plant cells and require the activity of glucosidases to release the corresponding toxic aglucones. In maize leaves, the most abundant benzoxazinoid is (2R)‐DIMBOA‐Glc, which is converted into the toxic DIMBOA upon herbivory. The ways in which three Spodoptera species metabolize this toxin were investigated. (2S)‐DIMBOA‐Glc, an epimer of the initial plant compound, was observed in the insect frass, and the associated glucosyltransferase activity was detected in the insect gut tissue. The epimeric glucoside produced by the insect was found to be no longer reactive towards plant glucosidases and thus cannot be converted into a toxin. Stereoselective reglucosylation thus represents a detoxification strategy in Spodoptera species that might help to explain their success as agricultural pests on benzoxazinoid‐containing crops. 相似文献
2.
E.M. Gershenzon M.E. Gershenzon G.N. Goltsman A.D. Semyonov A.V. Sergeev 《Solid State Communications》1984,50(3):207-212
The effect of heating electrons with respect to phonons in a thin superconducting film driven into the resistive state by the current and the external magnetic field has been observed and investigated. This effect caused by the electromagnetic radiation is manifested in the increased resistance of the film and is not selective over the frequency range from 1010 to 1015 Hz. That the effect is frequency independent under the conditions of strong electron scattering caused by static defects is explained by the decisive role of electron -electron collisions in forming the distribution function. The characteristic time of resistance change, obtained experimentally, corresponds to the relaxation time of the order parameter near the superconducting transition and to the relaxation time of the nonelastic electron-phonon interaction at lower temperatures and in lower magnetic fields. 相似文献
3.
Szöke E Máday E Gershenzon J Allen JL Lemberkovics E 《Journal of chromatographic science》2004,42(5):229-233
Gas chromatography (GC) and GC-mass spectrometry are used to identify a new sesqiterpene, beta-eudesmol, which seems to be a characteristic essential oil component of the intact and in vitro organized root of chamomile [Chamomilla recutita (L.) Rauschert]. It is identified on three types of stationary phases by GC. The confirmation of identity is carried out by comparison of mass spectra with those reported in the literature and measured from a reference compound. The percentage evaluation of the oil component is made by area normalization, on the basis of three parallel measurements. Among the cultivated and wild chamomile species examined, the wild species from the areas of Szeghalom contain the highest quantity of beta-eudesmol (9.25% in the total essential oil). 相似文献
4.
A. A. Verevkin N. G. Ptitsina K. V. Smirnov G. N. Gol’tsman E. M. Gershenzon K. S. Ingvesson 《JETP Letters》1996,64(5):404-409
The temperature dependence of the energy relaxation time τe (T) of a two-dimensional electron gas at an AlGaAs/GaAs heterointerface is measured under quasiequilibrium conditions in the
region of the transition from scattering by acoustic phonons to scattering with the participation of optical phonons. The
temperature interval of constant τe, where scattering by the deformation potential predominates, is determined. In the preceding, low-temperature region, where
piezoacoustic and deformation-potential-induced scattering processes coexist, τ e decreases slowly with increasing temperature. Optical phonons start to participate in the scattering processes at T∼25 K (the characteristic phonon lifetime was equal to τLOτ4.5 ps). The energy losses calculated from the τe data in a model with an effective nonequilibrium electron temperature agree with the published data obtained under strong
heating conditions.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 371–375 (10 September 1996) 相似文献
5.
A. V. Ivanov A. Yu. Zasypkin A. V. Stepanov Yu. M. Gershenzon 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(2):289-291
The paper describes a new source of surface organic radicals whose special feature is a low rate of the initiation of alkyl radicals in reactions of H atoms with the surface of alkanes. A special reactor design was used to accumulate radicals at room temperature and observe alkoxyl radicals RO by the EPR method. For this purpose, alkanes were deposited on aerosil and placed into an EPR cavity. Thanks to the large area of aerosil loads (~103 cm2), we were able to obtain a stable signal corresponding to a ~1017 total amount of alkoxyl radicals (the degree of surface coverage ~0.1%). When O2 was introduced into the reactor in concentrations of 1015–1016 cm?3, a sharp decrease in the signal from surface organic radicals was observed. The process was described as the first-order (RO) s + O2 → HO2 + ketone reaction with a 1.7 × 10?17 cm3 s?1 rate constant. 相似文献
6.
Ivanov AV Trakhtenberg S Bertram AK Gershenzon YM Molina MJ 《The journal of physical chemistry. A》2007,111(9):1632-1637
The diffusion of OH, HO2, and O3 in He, and of OH in air, has been investigated using a coated-wall flow tube reactor coupled to a chemical ionization mass spectrometry. The diffusion coefficients were determined from measurements of the loss of the reactive species to the flow tube wall as a function of pressure. On the basis of the experimental results, D(OH-He) = 662 +/- 33 Torr cm2 s-1, D(OH-air) = 165 +/- 20 Torr cm2 s-1, D(HO2-He) = 430 +/- 30 Torr cm2 s-1, and D(O3-He) = 410 +/- 25 Torr cm2 s-1 at 296 K. We show that the measured values for OH and HO2 are in better agreement with measured values of their polar analogues (H2O and H2O2) compared with measured values of their nonpolar analogues (O and O2). The measured value for OH in air is 25% smaller than that for O (the nonpolar analogue). The difference between the measured value for HO2 and O2 (the nonpolar analogue) in air is expected to be even larger. Also we show that calculations of the diffusion coefficients based on Lennard-Jones potentials are in excellent agreement with the measurements. This gives further confidence that these calculations can be used to estimate accurate diffusion coefficients for conditions where laboratory data currently do not exist. 相似文献
7.
SH Luo Y Liu J Hua XM Niu SX Jing X Zhao B Schneider J Gershenzon SH Li 《Organic letters》2012,14(16):4146-4149
The major pigment responsible for the dark brown nectar of the "bird's Coca cola tree", Leucosceptrum canum (Labiatae), was isolated and identified as a unique symmetric proline-quinone conjugate, 2,5-di-(N-(-)-prolyl)-para-benzoquinone (DPBQ). Behavioral experiments with both isolated and synthetic authentic samples indicated that DPBQ functions mainly as a color attractant to bird pollinators. 相似文献
8.
V.B. Rozenshtein Yu.M. Gershenzon S.D. Ilin O.P. Kishkovitch 《Chemical physics letters》1984,112(5):473-478
A combined EPR/LMR spectrometer and fast-flow system has been used to investigate the reactions HO2 + NO(k1), HO2 + OH(k2), HO2 + HO2(k3) at room temperature. The rate constants have been measured: k1 = (7.0 ± 0.6) × 10?12 cm3 s?1 (P = 7–10 Torr);k2 = (5.2 ± 1.2) × 10?11 cm3 s?1 (P = 8–10 Torr);k3 = (1.65 ± 0.3) × 10?12 cm3 s?1 (P = 2.1–24.9 Torr). The conclusion is drawn from analysis of the literature and the present work that k2 and k3 do not depend on pressure up to 1 atm. 相似文献
9.
10.
O-Methylated benzoxazinoids (BXs) and flavonoids are widespread defenses against herbivores and pathogens in the grasses (Poaceae). Recently, two flavonoid O-methyltransferases (FOMTs), ZmFOMT2 and ZmFOMT3, have been reported to produce phytoalexins in maize (Zea mays). ZmFOMT2 and ZmFOMT3 are closely related to the BX O-methyltransferases (OMTs) ZmBX10-12 and ZmBX14, suggesting a common evolutionary origin in the Poaceae. Here, we studied the evolution and enzymatic requirements of flavonoid and BX O-methylation activities in more detail. Using BLAST searches and phylogenetic analyses, we identified enzymes homologous to ZmFOMT2 and ZmFOMT3, ZmBX10-12, and ZmBX14 in several grasses, with the most closely related candidates found almost exclusively in species of the Panicoideae subfamily. Biochemical characterization of candidate enzymes from sorghum (Sorghum bicolor), sugar cane (Saccharum spp.), and teosinte (Zea nicaraguensis) revealed either flavonoid 5-O-methylation activity or DIMBOA-Glc 4-O-methylation activity. However, DIMBOA-Glc 4-OMTs from maize and teosinte also accepted flavonols as substrates and converted them to 3-O-methylated derivatives, suggesting an evolutionary relationship between these two activities. Homology modeling, sequence comparisons, and site-directed mutagenesis led to the identification of active site residues crucial for FOMT and BX OMT activity. However, the full conversion of ZmFOMT2 activity into BX OMT activity by switching these residues was not successful. Only trace O-methylation of BXs was observed, indicating that amino acids outside the active site cavity are also involved in determining the different substrate specificities. Altogether, the results of our study suggest that BX OMTs have evolved from the ubiquitous FOMTs in the PACMAD clade of the grasses through a complex series of amino acid changes. 相似文献