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71.
Leaves of Kalanchoë daigremontiana Hamet et Perr. at a photon flux density (PFD) above 220 mol·m–2s–1 (400–700 nm) or at leaf temperatures above 27.0 °C showed a rapid loss of rhythmicity, and a more or less pronounced damping-out of the endogenous circadian rhythm of CO2 exchange under continuous illumination. This rhythm was reinitiated after reduction of the PFD by 90–120 mol·m–2·s–1 or reduction of leaf temperature by 3.5–11.0 °C under otherwise unchanged external conditions. The reduction in the magnitude of the external control parameter of the Crassulacean acid metabolism (CAM) rhythm (i.e. PFD or leaf temperature) set the phase of the new rhythm. The maxima of CO2 uptake occurred about 5, 28, 51, 75 h after the reduction. Simulations with a CAM model under comparable conditions showed a similar behaviour. The influence of temperature on the endogenous CAM rhythm observed in K. daigremontiana in vivo could be simulated by incorporating into the model temperature-dependent switch modes for passive efflux of malate from the vacuole to the cytoplasm. Thus, the model indicates that tonoplast function plays an important role in regulation of the endogenous CAM rhythm in K. daigremontiana.Abbreviations CAM
Crassulacean acid metabolism
- PAR
photosynthetically active radiation
- PFD
photon flux density
This work was supported by a grant to F.B. and U.L. from Teilprojekt B5 in the Sonderforschungsbereich 199 of the Deutsche Forschungsgemeinschaft (Bonn, Germany) and by a grant to T. E. E. G. from the Sudienstiftung des deutschen Volkes (Bonn, Germany). Erika Ball is thanked for processing of time-course data for the analysis of Fourier spectra. 相似文献
72.
Antisense oligonucleotide containing an internal, non-nucleotide-based linker promote site-specific cleavage of RNA. 总被引:3,自引:3,他引:0 下载免费PDF全文
M A Reynolds T A Beck P B Say D A Schwartz B P Dwyer W J Daily M M Vaghefi M D Metzler R E Klem L J Arnold 《Nucleic acids research》1996,24(4):760-765
We have designed and synthesized a series of novel antisense methylphosphonate oligonucleotide (MPO) cleaving agents that promote site-specific cleavage on a complementary RNA target. These MPOs contain a non- nucleotide-based linking moiety near the middle of the sequence in place of one of the nucleotide bases. The region surrounding the unpaired base on the RNA strand (i.e. the one directly opposite the non-nucleotide-linker) is sensitive to hydrolytic cleavage catalyzed by ethylenediamine hydrochloride. Furthermore, the regions of the RNA comprising hydrogen bonded domains are resistant to cleavage compared with single-stranded RNA alone. Several catalytic moieties capable of supporting acid/base hydrolysis were coupled to the non-nucleotide-based linker via simple aqueous coupling chemistries. When tethered to the MPO in this manner these moieties are shown to catalyze site-specific cleavage on the RNA target without any additional catalyst. 相似文献
73.
Membrane inlet mass spectrometry has been used for the characterization of halogenated organic compounds produced by the fungus Bjerkandera adusta. Using this technique we obtained electron impact-, chemical ionization-, electron capture negative chemical ionization-mass spectra and tandem mass spectra directly from the growth medium. Through this direct analysis of the samples we identified novel bioconversion products and confirmed recently published data on the production of both chlorinated and brominated methoxybenzaldehyde metabolites. Growth profiles of the culture grown on a defined medium showed that the production of secondary metabolites starts after approximately 6 days and reaches maximal concentrations of 25-250 muM after 15-20 days. Although delayed, the production of secondary metabolites paralleled a depletion of glucose from the medium and stopped shortly after all glucose had been consumed. Experiments in which fluoro- and bromo-labeled 4-methoxybenzaldehydes were added to the medium at day 8 showed biotransformation of these compounds into chloro-3-fluoro-4-methoxy-benzaldehyde and chloro-3-bromo-4-methoxybenzaldehyde, respectively. No dichlorinated products were observed, suggesting that halogenation takes place only at the meta position on the 4-methoxybenzaldehydes. These experiments are the first to bring direct evidence of a halogenation mechanism, where the enzymatic attack takes place directly on the 4-methoxybenzaldehyde intermediates. (c) John Wiley & Sons, Inc. 相似文献
74.
Ole Kirk Morten Wü rtz Christensen Frederik Beck Ture Damhus 《Biocatalysis and Biotransformation》1995,12(2):91-97
In the development of an efficient synthesis of 1-O-decanoyl-2,3,4,6-tetra-O-acetyl-β-D-glucose (β-2) several lipase-based approaches have been explored. Among five immobilized Upases tested, the lipase from Candida antarctica proved particularly efficient for catalyzing selective hydrolysis in the 1-position of 1,2,3,4,6-penta-O-acetyl-β-D-glucose (β-1). Using triethylamine as catalyst, the hydrolysis product 2,3,4,6-tetra-O-acetyl-D-glucose (3) can be esterified with decanoyl chloride to form β-2 selectively, thereby providing an efficient chemo-enzymatic synthesis starting from readily available raw materials. Attempts to produce β-2 from β-1 by lipase-catalyzed interesterification or to esterify 3 with decanoic acid using a lipase as catalyst were unsuccessful. The latter finding was explained by the hemiacetal OH group of glucose being unable to act as nucleophile in the lysis of the lipase acyl-enzyme intermediate. Furthermore, β-2 was found to bee a too bulky substrate to fit into the active site of any of the lipases tested. 相似文献
75.
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78.
John S. Beck Anne E. Kwitek Phillip H. Cogen Andrew K. Metzger Geoffrey M. Duyk Val C. Sheffield 《Human genetics》1993,91(1):25-30
p53 is a tumor suppressor gene located on 17p, a region of the human genome frequently deleted in tumors. Mutation of the p53 gene is an important step leading to development of many forms of human cancer. To simplify the analysis of tumors for p53 point mutations, we describe a GC-clamped denaturing gradient gel assay for detecting single-base substitutions within highly conserved regions of the p53 gene. This assay alows for efficient screening of tumors for single-base substitutions within the p53 gene and can be used to facilitate sequence analysis of p53 point mutations. 相似文献
79.
Four genes specifically expressed during gametogenesis of Chlamydomonas reinhardtii have been cloned and their expression patterns analyzed. mRNAs encoded by these gamete-specific genes (gas) were absent or present only at very low levels in vegetative cells and mature zygotes. In young zygotes 2 h after gamete fusion, the mRNAs of three gas genes still persisted. The gas mRNAs accumulated during gametic differentiation. The temporal patterns of accumulation of individual mRNAs differed; some started to increase early during gametogenesis, others accumulated in the late phase. The accumulation of one of the late mRNAs (gas28) was stricly light-dependent. To illustrate the utility of the genes cloned in the analysis of sexual differentiation in Chlamydomonas reinhardtii we show that in a gametogenesis-defective mutant, the expression of late genes is prevented while that of early genes is normal. 相似文献
80.
Holger Stephan Stefan Freund Werner Beck Günther Jung Jean-Marie Meyer Günther Winkelmann 《Biometals》1993,6(2):93-100
Novel linear hydroxamate/hydroxycarboxylate siderophores from strains of Pseudomonas cepacia were isolated and named ornibactins. The ornibactins represent modified tetrapeptide siderophores, possessing the sequence l-Orn1(N
-OH, N
-acyl)-d-threo-Asp(-OH)-l-Ser-l-Orn4(N
-OH, N
-formyl)-1,4-diaminobutane. The N
-acyl groups of Orn1(N
-OH, N
-acyl) may vary and represent the three acids 3-hydroxybutanoic acid, 3-hydroxyhexanoic acid and 3-hydroxyoctanoic acid, leading to a mixture of three different ornibactins, designated according to their acyl chain length as ornibactin-C4, ornibactin-C6 and ornibactin-C8. Each of the siderophores is accompanied by a small amount of a more hydrophilic component with a 16 a.m.u. higher mass. The structure elucidation was based on results from gas chromatography amino acid analysis, electrospray mass spectrometry, and one- and two-dimensional nuclear magnetic resonance techniques. 相似文献