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排序方式: 共有515条查询结果,搜索用时 31 毫秒
31.
In vitro induction of tetraploidy in mulberry (Morus alba L.) 总被引:6,自引:0,他引:6
A high frequency of tetraploidy was induced in mulberry (Morus alba L.) through apical bud treatment under in vitro conditions. Apical buds from in vitro-grown plants were treated with three different concentrations (0.05, 0.1 and 0.2%)
of colchicine in MS medium for 24 h. Tetraploidy at a frequency of 39.4±4.8% was obtained using 0.1% colchicine, whereas the
frequency of tetraploidy was significantly reduced to 16.7±2.3% when 0.2% colchicine was used. Morphological, histological
and cytological evidence indicated a phenotypic and genomic similarity of in vitro- with ex vitro-induced tetraploids. Rooting
of tetraploids was on basal medium containing 2.6 μm NAA. The recovery of tetraploids was 80.8% more efficient using the in vitro method instead of the ex vitro method. The use
of the same colchicine medium for up to 4 weeks with additional explants was found to be equally effective for the induction
of tetraploidy.
Received: 6 January 1997 / Revision received: 6 October 1997 / Accepted: 12 December 1997 相似文献
32.
Wen-Yi Chen Dileep K. Pulukkunat I-Ming Cho Hsin-Yue Tsai Venkat Gopalan 《Nucleic acids research》2010,38(22):8316-8327
RNase P catalyzes the Mg2+-dependent 5′-maturation of precursor tRNAs. Biochemical studies on the bacterial holoenzyme, composed of one catalytic RNase P RNA (RPR) and one RNase P protein (RPP), have helped understand the pleiotropic roles (including substrate/Mg2+ binding) by which a protein could facilitate RNA catalysis. As a model for uncovering the functional coordination among multiple proteins that aid an RNA catalyst, we use archaeal RNase P, which comprises one catalytic RPR and at least four RPPs. Exploiting our previous finding that these archaeal RPPs function as two binary RPP complexes (POP5•RPP30 and RPP21•RPP29), we prepared recombinant RPP pairs from three archaea and established interchangeability of subunits through homologous/heterologous assemblies. Our finding that archaeal POP5•RPP30 reconstituted with bacterial and organellar RPRs suggests functional overlap of this binary complex with the bacterial RPP and highlights their shared recognition of a phylogenetically-conserved RPR catalytic core, whose minimal attributes we further defined through deletion mutagenesis. Moreover, single-turnover kinetic studies revealed that while POP5•RPP30 is solely responsible for enhancing the RPR’s rate of precursor tRNA cleavage (by 60-fold), RPP21•RPP29 contributes to increased substrate affinity (by 16-fold). Collectively, these studies provide new perspectives on the functioning and evolution of an ancient, catalytic ribonucleoprotein. 相似文献
33.
Dev Chandran Kolli Bhaktavatsala Reddy Shahana Pallichera Vijayan Parthasarthy Sugumar Gudavalli Sudha Rani Ponsekaran Santha Kumar Lingala Rajendra Villuppanoor Alwar Srinivasan 《Indian journal of microbiology》2010,50(3):266-274
Peste des Petits Ruminants (PPR) is a highly contagious animal disease caused by the Peste des Petits Ruminants virus (PPRV) belonging to the genus morbillivirus and family Paramyxoviridae. The disease results in high morbidity and mortality
in goats, sheep and in some small wild ruminants. The presence of large number of small ruminants reared in endemic areas
makes PPR a notorious disease threatening the livelihood of poor farmers. Conventional vaccination using a live, attenuated
vaccine gives adequate protection but cannot be used in case of eradication of the disease due to difficulty in differentiation
of infected animals from the vaccinated ones. 相似文献
34.
R. K. Sharma M. S. Negi S. Sharma P. Bhardwaj R. Kumar E. Bhattachrya S. B. Tripathi D. Vijayan A. R. Baruah S. C. Das B. Bera R. Rajkumar J. Thomas R. K. Sud N. Muraleedharan M. Hazarika M. Lakshmikumaran S. N. Raina P. S. Ahuja 《Biochemical genetics》2010,48(7-8):549-564
India has a large repository of important tea accessions and, therefore, plays a major role in improving production and quality of tea across the world. Using seven AFLP primer combinations, we analyzed 123 commercially important tea accessions representing major populations in India. The overall genetic similarity recorded was 51%. No significant differences were recorded in average genetic similarity among tea populations cultivated in various geographic regions (northwest 0.60, northeast and south both 0.59). UPGMA cluster analysis grouped the tea accessions according to geographic locations, with a bias toward China or Assam/Cambod types. Cluster analysis results were congruent with principal component analysis. Further, analysis of molecular variance detected a high level of genetic variation (85%) within and limited genetic variation (15%) among the populations, suggesting their origin from a similar genetic pool. 相似文献
35.
Selvaraj M Roy S Singh NS Sangeetha R Varshney U Vijayan M 《Journal of molecular biology》2007,372(1):186-193
Peptidyl-tRNA hydrolase cleaves the ester bond between tRNA and the attached peptide in peptidyl-tRNA in order to avoid the toxicity resulting from its accumulation and to free the tRNA available for further rounds in protein synthesis. The structure of the enzyme from Mycobacterium tuberculosis has been determined in three crystal forms. This structure and the structure of the enzyme from Escherichia coli in its crystal differ substantially on account of the binding of the C terminus of the E. coli enzyme to the peptide-binding site of a neighboring molecule in the crystal. A detailed examination of this difference led to an elucidation of the plasticity of the binding site of the enzyme. The peptide-binding site of the enzyme is a cleft between the body of the molecule and a polypeptide stretch involving a loop and a helix. This stretch is in the open conformation when the enzyme is in the free state as in the crystals of M. tuberculosis peptidyl-tRNA hydrolase. Furthermore, there is no physical continuity between the tRNA and the peptide-binding sites. The molecule in the E. coli crystal mimics the peptide-bound enzyme molecule. The peptide stretch referred to earlier now closes on the bound peptide. Concurrently, a channel connecting the tRNA and the peptide-binding site opens primarily through the concerted movement of two residues. Thus, the crystal structure of M. tuberculosis peptidyl-tRNA hydrolase when compared with the crystal structure of the E. coli enzyme, leads to a model of structural changes associated with enzyme action on the basis of the plasticity of the molecule. 相似文献
36.
Athanasiou A Clarke AB Turner AE Kumaran NM Vakilpour S Smith PA Bagiokou D Bradshaw TD Westwell AD Fang L Lobo DN Constantinescu CS Calabrese V Loesch A Alexander SP Clothier RH Kendall DA Bates TE 《Biochemical and biophysical research communications》2007,364(1):131-137
Time-lapse microscopy of human lung cancer (H460) cells showed that the endogenous cannabinoid anandamide (AEA), the phyto-cannabinoid Δ-9-tetrahydrocannabinol (THC) and a synthetic cannabinoid HU 210 all caused morphological changes characteristic of apoptosis. Janus green assays of H460 cell viability showed that AEA and THC caused significant increases in OD 595 nm at lower concentrations (10-50 μM) and significant decreases at 100 μM, whilst HU 210 caused significant decreases at all concentrations. In rat heart mitochondria, all three ligands caused significant decreases in oxygen consumption and mitochondrial membrane potential. THC and HU 210 caused significant increases in mitochondrial hydrogen peroxide production, whereas AEA was without significant effect. All three ligands induced biphasic changes in either mitochondrial complex I activity and/or mitochondrial complex II-III activity. These data demonstrate that AEA, THC, and HU 210 are all able to cause changes in integrated mitochondrial function, directly, in the absence of cannabinoid receptors. 相似文献
37.
Kim SJ Zhang X Xu X Chen A Gonzalez JB Koul S Vijayan K Crystal GJ Vatner SF Hintze TH 《American journal of physiology. Heart and circulatory physiology》2007,292(5):H2152-H2158
Nitric oxide (NO) derived from endothelial NO synthase (NOS) (eNOS) has been identified as a trigger for the second window of protection (SWOP), but its role as a mediator during the SWOP is a matter of debate. Eighteen mongrel dogs were chronically instrumented to measure left ventricular function, coronary blood flow, and wall thickening. Myocardial preconditioning was induced by 10 min coronary artery occlusion. After 24 h of reperfusion (during the SWOP), the hearts were excised. Coronary microvessels were isolated and incubated in presence of 1) the endothelium-dependent agonists carbachol and bradykinin, 2) the calcium ionophore A23187, and 3) the angiotensin-converting enzyme (ACE) inhibitors enalaprilat and ramiprilat. Nitrite, a metabolite of NO, was measured. Under baseline conditions, nitrite production in microvessels from SWOP was 30% higher than that from normal (96 +/- 4 vs. 74 +/- 3 pmol/mg, P < 0.01, respectively). Nitrite production in response to carbachol, bradykinin, and A23187 was also enhanced in microvessels from SWOP (P < 0.05). These enhanced responses were abolished by N(G)-nitro-l-arginine methyl ester (l-NAME) or the endothelial receptor-specific antagonists atropine and HOE-140. The level of eNOS protein in the SWOP myocardium was twofold higher than that in the non-SWOP myocardium. Nitrite production in response to the ACE inhibitors was greater in microvessels from SWOP. These effects were blocked by l-NAME, HOE-140, or dichloroisocoumarin (which inhibits kinin formation). We found that a brief ischemic episode induced delayed, enhanced NO production in coronary microvessels and an upregulation of eNOS protein. These findings suggest that eNOS is a mediator during the SWOP. The ability of ACE inhibitors to enhance NO release during the SWOP points to an additional clinical application for these drugs. 相似文献
38.
In present studies, the new optical sensing platform based on optical planar waveguide (OPWG) for sucrose estimation was reported. An evanescent-wave biosensor was designed by using novel agarose–guar gum (AG) biopolymer composite sol–gel with entrapped enzymes (acid invertase (INV) and glucose oxidase (GOD)). Partially purified watermelon invertase isolated from Citrullus vulgaris fruit (specific activity 832 units mg−1) in combination with GOD was physically entrapped in AG sol–gel and cladded on the surface of optical planar waveguide. Na+–K+ ion-exchanged glass optical waveguides were prepared and employed for the fabrication of sucrose biosensor. By addressing the enzyme modified waveguide structure with, the optogeometric properties of adsorbed enzyme layer (12 μm) at the sensor solid–liquid interface were studied. The OPWG sensor with short response time (110 s) was characterized using the 0.2 M acetate buffer, pH 5.5. The fabricated sucrose sensor showed concentration dependent linear response in the range 1 × 10−10 to 1 × 10−6 M of sucrose. Lower limit of detection of this novel AG–INV–GOD cladded OPWG sensor was found to be 2.5 × 10−11 M sucrose, which indicates that the developed biosensor has higher sensitivity towards sucrose as compared to earlier reported sensors using various transducer systems. Biochips when stored at room temperature, showed high stability for 81 days with 80% retention of original sensitivity. These sucrose sensing biochips showed good operational efficiency for 10 cycles. The proper confinement of acid invertase and glucose oxidase in hydrogel composite was confirmed by scanning electron microscopy (SEM) images. The constructed OPWG sensor is versatile, easy to fabricate and can be used for sucrose measurements with very high sensitivity. 相似文献
39.
Vijayan S 《MedGenMed : Medscape general medicine》2007,9(4):41
The World Health Organization (WHO) can be considered the primary agency of the United Nations that promotes global public health. This article provides a general overview of WHO by exploring the history, current, and future practices of the organization, and by addressing its major roles and functions in the present day. BACKGROUND: Srimathy Vijayan is a fourth-year medical student at the University of East Anglia, Norwich, United Kingdom. She interned at the WHO headquarters in Geneva during the summer of 2007. 相似文献
40.