The enzymatic incorporation of isopentenyl pyrophosphate into polyisoprene in rubber particles from Parthenium argentatum Gray     

C.R. Benedict  C.L. RosenfieldRachel Goss  Paul J. Greer  M.A. Foster 《Industrial Crops and Products》2012,35(1):172-177

Studies have indicated the presence of both a de novo biosynthesis of new polyisoprene chains and the elongation of pre-existing rubber-PP chains in rubber particles from Ficus elastica Roxb. and small rubber particles from Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg. In this paper, we have isolated rubber particles from the cortical parenchyma of Parthenium argentatum Gray with an adsorbed isopentenyl pyrophosphate isomerase that was competent to form polyisoprene to determine the presence of de novo biosynthesis of polyisoprene and the elongation of pre-existing rubber-PP. The gel filtrated rubber particles were supplied saturating concentrations of [¹⁴C]-isopentenyl pyrophosphate for 1 h and the resulting concentrations of [¹⁴C]-polyisoprene were isolated and analyzed with a Waters 150C Gel Permeation Chromatograph. The mol wt distribution of the [¹⁴C]-polyisoprene ranged from 10³ to 10⁶ Da with no formation of high mol wt chains equal to the polyisoprene in the mol wt distribution of natural rubber from P. argentatum. The mol wt distribution of [¹⁴C]-polyisoprene following 1 h of incubation of the reaction mixture was similar to the mol wt distribution formed by the bound rubber transferase in washed rubber particles of H. brasiliensis and the time-dependent formation of polyisoprene by washed rubber particles from P. argentatum. The data support the conclusion that the washed rubber particles from P. argentatum contain a bound rubber transferase that initiates the formation of new chains of polyisoprene from the dimethylallyl pyrophosphate initiator generated from the added isopentenyl pyrophosphate isomerase followed by the extensive polymerization of isopentenyl pyrophosphate to form a monomodal rubber polymer. There was no evidence in these washed rubber particles of a chain elongation of pre-existing rubber-PP.  相似文献   

The formation of rubber particles in developing cortical parenchyma of Parthenium argentatum plants exposed to the low temperatures of fall and winter of the Chihuahuan Desert     

C.R. Benedict  Rachel Goss  M.A. Foster  Paul J. Greer   《Industrial Crops and Products》2009,30(3):403-406

In this paper we have examined rubber particle formation in cortical parenchyma cells of guayule (Parthenium argentatum Gray) plants exposed to the low temperature of the fall and winter of the Chihuahuan Desert that stimulates rubber formation.Plants were transplanted to field plots in May in Ft. Stockton, TX. In September most of the cortical parenchyma in cross-sections 3 cm from the stem tips and from the base of the stems were mature, containing a central vacuole, tonoplast and a parietal cytosol with chloroplasts, mitochondria, peroxisomes and a few rubber particles. In 8-month-old plants examined in January many of the cortical parenchyma cells 3 cm from the stem tip were immature and completely filled with cytosol containing a high population of rubber particles. At this stage of development there was a thickened secondary cell wall but no central vacuole, tonoplast or parietal cytosol and all the rubber particles were formed in the central cytosol. In the cortical parenchyma in early stages of central vacuole development, by the coalescing of microvacuoles, the rubber particles were located in the developing central vacuole and in the cytosol being appressed toward the cell wall. In 8-month-old plants in January, the cortical parenchyma at the base of the stems was more mature than cells near the stem tips. These cells showed a later stage of development of a central vacuole from microvacuole fusing and contained a high population of mixed sizes of rubber particles and a thin layer of parietal cytosol containing chloroplasts, mitochondria and rubber particles with a partly developed tonoplast. There was clear evidence of the fusion of small rubber particles with other rubber particles that may represent a mechanism for the growth of rubber particles.  相似文献   

Growth hormone and ghrelin receptor genes are differentially expressed between genetically lean and fat selection lines of sheep   总被引：1，自引：0，他引：1  

French MC  Littlejohn RP  Greer GJ  Bain WE  McEwan JC  Tisdall DJ 《Journal of animal science》2006,84(2):324-331

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Short‐Term Antiandrogen Flutamide Treatment Causes Structural Alterations in Somatic Cells Associated with Premature Detachment of Spermatids in the Testis of Pubertal and Adult Guinea Pigs     

LR Maschio  RS Cordeiro  SR Taboga  RM Góes 《Reproduction in domestic animals》2010,45(3):516-524

In spite of widespread application of flutamide in the endocrine therapies of young and adult patients, the side effects of this antiandrogen on spermatogenesis and germ‐cell morphology remain unclear. This study evaluates the short‐term androgen blockage effect induced by the administration of flutamide to the testes of pubertal (30‐day old) and adult (65‐ and 135‐day old) guinea pigs, with an emphasis on ultrastructural alterations of main cell types. The testes removed after 10 days of treatment with either a non‐steroidal antiandrogen, flutamide (10 mg/kg of body weight) or a pharmacological vehicle alone were processed for histological, quantitative and ultrastructural analysis. In pubertal animals, flutamide androgenic blockage induces spermatogonial differentiation and accelerates testes maturation, causing degeneration and detachment of primary spermatocytes and round spermatids, which are subsequently found in great quantities in the epididymis caput. In post‐pubertal and adult guinea pigs, in addition to causing germ‐cell degeneration, especially in primary spermatocytes, and leading to the premature detachment of spherical spermatids, the antiandrogen treatment increased the relative volume of Leydig cells. In addition, ultrastructural evaluation indicated that irrespective of age antiandrogen treatment causes an increase in frequency of organelles involved with steroid hormone synthesis in the Leydig cells and a dramatic accumulation of myelin figures in their cytoplasm and, to a larger degree, in Sertoli cells. In conclusion, the transient exposition of the guinea pigs to flutamide, at all postnatal ages causes some degenerative lesions including severe premature detachment of spermatids and accumulation of myelin bodies in Leydig and Sertoli cells, compromising, at least temporarily, the spermatogenesis.  相似文献   

Chirality in synthetic agrochemicals: bioactivity and safety considerations     

N Kurihara  J Miyamoto  GD Paulson  B Zeeh  MW Skidmore  RM Hollingworth  HA Kuiper 《Pest management science》1999,55(2):219-219

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Penny ice cap cores, baffin island, canada, and the wisconsinan foxe dome connection: two states of hudson bay ice cover     

DA Fisher  RM Koerner  JC Bourgeois  G Zielinski  C Wake  CU Hammer  HB Clausen  N Gundestrup  S Johnsen  K Goto-Azuma  T Hondoh  E Blake  M Gerasimoff 《Science (New York, N.Y.)》1998,279(5351):692-695

Ice cores from Penny Ice Cap, Baffin Island, Canada, provide continuous Holocene records of oxygen isotopic composition (delta18O, proxy for temperature) and atmospheric impurities. A time scale was established with the use of altered seasonal variations, some volcanic horizons, and the age for the end of the Wisconsin ice age determined from the GRIP and GISP2 ice cores. There is pre-Holocene ice near the bed. The change in delta18O since the last glacial maximum (LGM) is at least 12.5 per mil, compared with an expected value of 7 per mil, suggesting that LGM ice originated at the much higher elevations of the then existing Foxe Dome and Foxe Ridge of the Laurentide Ice Sheet. The LGM delta18O values suggest thick ice frozen to the bed of Hudson Bay.  相似文献   

Strong regularities in world wide web surfing   总被引：5，自引：0，他引：5  

BA Huberman  PLT Pirolli  JE Pitkow  RM Lukose 《Science (New York, N.Y.)》1998,280(5360):95-97

One of the most common modes of accessing information in the World Wide Web is surfing from one document to another along hyperlinks. Several large empirical studies have revealed common patterns of surfing behavior. A model that assumes that users make a sequence of decisions to proceed to another page, continuing as long as the value of the current page exceeds some threshold, yields the probability distribution for the number of pages that a user visits within a given Web site. This model was verified by comparing its predictions with detailed measurements of surfing patterns. The model also explains the observed Zipf-like distributions in page hits observed at Web sites.  相似文献   

The structure of the upper atmosphere of mars: In situ accelerometer measurements from mars global surveyor   总被引：1，自引：0，他引：1  

GM Keating  SW Bougher  RW Zurek  RH Tolson  GJ Cancro  SN Noll  JS Parker  TJ Schellenberg  RW Shane  BL Wilkerson  JR Murphy  JL Hollingsworth  RM Haberle  M Joshi  JC Pearl  BJ Conrath  MD Smith  RT Clancy  RC Blanchard  RG Wilmoth  DF Rault  TZ Martin  DT Lyons  PB Esposito  MD Johnston  al et 《Science (New York, N.Y.)》1998,279(5357):1672-1676

The Mars Global Surveyor (MGS) z-axis accelerometer has obtained over 200 vertical structures of thermospheric density, temperature, and pressure, ranging from 110 to 170 kilometers, compared to only three previous such vertical structures. In November 1997, a regional dust storm in the Southern Hemisphere triggered an unexpectedly large thermospheric response at mid-northern latitudes, increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm. Throughout the MGS mission, thermospheric density bulges have been detected on opposite sides of the planet near 90 degreesE and 90 degreesW, in the vicinity of maximum terrain heights. This wave 2 pattern may be caused by topographically-forced planetary waves propagating up from the lower atmosphere.  相似文献   

Model structure for the inflammatory protein C5a   总被引：6，自引：0，他引：6  

J Greer 《Science (New York, N.Y.)》1985,228(4703):1055-1060

The complement cleavage product C5a is a potent stimulant of inflammatory processes; thus, inhibition of C5a activity is of therapeutic interest. The three-dimensional structure of the major portion of C5a was modeled from the homologous C3a crystal structure by comparative modeling techniques. The model shows that core residues of C5a are completely conserved, while external residues differ from C3a. Even though the amino-terminal 12 residues of C3a are disordered in the crystal, this sequence in C5a may form an amphipathic helix. The distribution of species sequence differences in the complete C5a structure suggests a possible receptor binding site.  相似文献   

Leukoencephalomalacia in horses     

RM CHRISTLEY  AP BEGG  DR HUTCHINS  DR HODGSON  WL BRYDEN 《Australian veterinary journal》1993,70(6):225-226

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