共查询到20条相似文献,搜索用时 31 毫秒
1.
Summary. The plant plasma membrane (PM) contains more than one b-type cytochrome. One of these proteins has a rather high redox potential (can be fully reduced by ascorbate) and is capable
of transporting electrons through the PM. Four genes encoding proteins with considerable homology to the sequences of cytochrome
b
561 proteins in the animal chromaffin granule membrane have recently been identified in the genome of Arabidopsis thaliana. In order to characterize the cytochrome b
561 located in the Arabidopsis PM, first PM vesicles were purified by aqueous polymer two-phase partitioning from the leaves
of 9-week-old A. thaliana. PM proteins were solubilized by nonionic detergent, and the fully ascorbate-reducible b-type cytochrome was partially purified by anion-exchange chromatography steps. Potentiometric redox titration of the fraction,
containing the fully ascorbate-reducible b-type cytochrome after the first anion-exchange chromatography step, revealed the presence of two hemes with redox potentials
of 135 mV and 180 mV, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the fractions containing
the fully ascorbate-reducible b-type cytochrome after the second anion-exchange chromatography step revealed the presence of a single polypeptide band at
about 120 kDa. However, heat treatment (15 min, 90 °C) before electrophoresis was able to split the 120 kDa band into two
bands with molecular masses of about 23 and 28 kDa. These values are lower than the apparent molecular mass for the fully
ascorbate-reducible b-type cytochrome purified from Phaseolus vulgaris hypocotyls (about 52 kDa) but are in good agreement with those characteristic for the cytochrome b
561 proteins purified from chromaffin granule membranes (about 28 kDa) and the four polypeptides predicted from the Arabidopsis
genome (24–31 kDa).
Received May 4, 2002; accepted July 26, 2002; published online May 21, 2003
RID="*"
ID="*" Correspondence and reprints: Institute of Biophysics, BRC, Hungarian Academy of Sciences, POB 521, 6701 Szeged, Hungary. 相似文献
2.
Biochemical entities involved in reactive oxygen species generation by human spermatozoa 总被引:3,自引:0,他引:3
Summary. Spermatozoa were the first cell type suggested to generate reactive oxygen species. However, a lack of standardization in
sperm preparation techniques and the obfuscating impact of contaminating cell types in human ejaculates have made it difficult
to confirm that mammalian germ cells do, in fact, make such reactive metabolites. By identifying, on a molecular level, those
entities involved in reactive oxygen species generation and demonstrating their presence in spermatozoa, the role of redox
chemistry in the control of sperm function can be elucidated. Two major proteins have apparently been identified in this context,
namely, NOX5, a calcium-activated NADPH oxidase, and nitric oxide synthase. Understanding the involvement of these enzymes
in sperm physiology is essential if we are to understand the causes of oxidative stress in the male germ line.
Received May 2, 2002; accepted July 26, 2002; published online May 21, 2003
RID="*"
ID="*" Correspondence and reprints: Discipline of Biological Sciences, University of Newcastle, Callaghan, NSW 2308, Australia. 相似文献
3.
Summary. Anaerobically light-grown cells of Rhodobacter capsulatus B100 are highly resistant to the toxic oxyanion tellurite (TeO3
2−; minimal inhibitory concentration, 250 μg/ml). This study examines, for the first time, some structural and biochemical features
of cells and plasma membrane fragments of this facultative phototroph grown in the presence of 50μg of K2TeO3 per ml. Through the use of transmission microscopy and X-ray microanalysis we show that several “needlelike” shaped granules
of elemental tellurium are accumulated into the cytosol near the intracytoplasmic membrane system. Flash-spectroscopy, oxygen
consumption measurements, and difference spectra analysis indicated that membrane vesicles (chromatophores) isolated from
tellurite-grown cells are able to catalyze both photosynthetic and respiratory electron transport activities, although they
are characterized by a low c-type cytochrome content (mostly soluble cytochrome c
2). This feature is paralleled by a low cytochrome c oxidase activity and with an NADH-dependent respiration which is catalyzed by a pathway leading to a quinol oxidase (Qox)
inhibited by high (millimolar) concentrations of cyanide (CN−). Conversely, membranes from R. capsulatus B100 cells grown in the absence of tellurite are characterized by a branched respiratory chain in which the cytochrome c oxidase pathway (blocked by CN− in the micromolar range) accounts for 35–40% of the total NADH-dependent oxygen consumption, while the remaining activity
is catalyzed by the quinol oxidase pathway. These data have been interpreted to show that tellurite resistance of R. capsulatus B100 is characterized by the presence of a modified plasma-membrane-associated electron transport system.
Received May 2, 2002; accepted July 26, 2002; published online May 21, 2003
RID="*"
ID="*" Correspondence and reprints: Department of Biology, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy. 相似文献
4.
Summary. Superoxide synthase and superoxide dismutase activity have been monitored in isolated maize (Zea mays) root plasma membranes spectrophotometrically by determination of nitro-blue tetrazolium and cytochrome c reduction, respectively. Superoxide production was induced by NADH and NADPH, with similar kinetics and approaching saturation
at 0.06 mM in the case of NADPH and 0.1 mM in the case of NADH, with rates of 18.6 ± 5.0 and 21.8 ± 7.2 nmol/min · mg of protein,
respectively. These activities exhibited a broad pH optimum between pH 6.5 and 7.5. Diphenylene iodonium inhibited about 25%
(10 μM DPI) and 40% (100 μM DPI) of this activity, imidazole inhibited about 20%, while KCN, a peroxidase inhibitor, did not
show any significant inhibition. Superoxide-dismutating activity was shown to occur in the same isolates and depended on the
quantity of plasma membrane protein present. Growth of plants on salicylic acid prior to membrane isolation induced a rise
in the activity of both of the enzymes by 20–35%, suggesting their coordinated action.
Received May 15, 2002; accepted September 30, 2002; published online May 21, 2003
RID="*" 相似文献
5.
We establish the existence of traveling front solutions and small amplitude traveling wave train solutions for a reaction-diffusion
system based on a predator-prey model with Holling type-II functional response. The traveling front solutions are equivalent
to heteroclinic orbits in R
4
and the small amplitude traveling wave train solutions are equivalent to small amplitude periodic orbits in R
4
. The methods used to prove the results are the shooting argument and the Hopf bifurcation theorem.
Received: 25 May 2001 / Revised version: 5 August 2002 / Published online: 19 November 2002
RID="*"
ID="*" Research was supported by the National Natural Science Foundations (NNSF) of China.
RID="*"
ID="*" Research was partially supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada. On leave
from the Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada.
Mathematics Subject Classification (2000): 34C35, 35K57
Key words or phrases: Traveling wave solution – Wazewski set – Shooting argument – Hopf bifurcation
Acknowledgements. We would like to thank the two referees for their careful reading and helpful comments. 相似文献
6.
Summary. Sphingomyelin is an abundant constituent of the plasma membranes of mammalian cells. Ceramide, its primary catabolic intermediate,
has emerged as an important lipid signaling molecule. Previous work carried out by our group has documented that plasma membrane
Mg2+-dependent neutral sphingomyelinase can be effectively inhibited by exogenous ubiquinol. In this work, we have tested whether
or not plasma-membrane-associated electron transport can also achieve this inhibition through endogenous ubiquinol. Our results
have shown that Mg2+-dependent neutral sphingomyelinase in isolated plasma membranes was inhibited by NAD(P)H under conditions where ubiquinone
is reduced to ubiquinol. This inhibition was potentiated in the presence of an extra amount of NAD(P)H:(quinone acceptor)
oxidoreductase 1 (EC 1.6.99.2). Depletion of plasma membranes from lipophilic antioxidants by solvent extraction abolished
the inhibition by reduced pyridine nucleotides without affecting the sensitivity of the neutral sphingomyelinase to exogenous
ubiquinol. Reconstitution of plasma membranes with ubiquinone restored the ability of NAD(P)H to inhibit the enzyme. Our results
support that the reduction of endogenous ubiquinone to ubiquinol by NAD(P)H-driven electron transport may regulate the activity
of the plasma membrane neutral sphingomyelinase.
Received May 20, 2002; accepted September 20, 2002; published online May 21, 2003
RID="**"
ID="**" Present address: Department of Biomedical Engineering, School of Medicine, University of Baltimore, Maryland, U.S.A.
RID="*"
ID="*" Correspondence and reprints: Departamento de Biología Celular, Fisiología e Inmunología, Facultad de Ciencias, Edificio
C-6, Campus Rabanales, Universidad de Córdoba, 14014 Córdoba, Spain. 相似文献
7.
We introduce inhomogeneous, substrate dependent cell division in a time discrete, nonlinear matrix model of size-structured
population growth in the chemostat, first introduced by Gage et al. [8] and later analysed by Smith [13]. We show that mass conservation is verified, and conclude that our system admits one
non zero globally stable equilibrium, which we express explicitly. Then we run numerical simulations of the system, and compare
the predictions of the model to data related to phytoplankton growth, whose obtention we discuss. We end with the identification
of several parameters of the system.
Received: 9 February 2000 / Revised version: 10 October 2001 / Published online: 23 August 2002
RID="*"
ID="*" Present address: Department of Mathematics and Statistics, University of Victoria, B.C., Canada. e-mail: jarino@math.uvic.ca
Key words or phrases: Chemostat – Structured population models – Discrete model – Inhomogeneous division size 相似文献
8.
Summary. Atomic models possessing the common structural features identified for the cytochrome b
561 (cyt b
561) protein family are presented. A detailed and extensive sequence analysis was performed in order to identify and characterize
protein sequences in this family of transmembrane electron transport proteins. According to transmembrane helix predictions,
all sequences contain 6 transmembrane helices of which 2–6 are located closely in the same regions of the 26 sequences in
the alignment. A mammalian (Homo sapiens) and a plant (Arabidopsis thaliana) sequence were selected to build 3-dimensional structures at atomic detail using molecular modeling tools. The main structural
constraints included the 2 pairs of heme-ligating His residues that are fully conserved in the family and the lipid-facing
sides of the helices, which were also very well conserved. The current paper proposes 3-dimensional structures which to our
knowledge are the first ones for any protein in the cyt b
561 family. The highly conserved His residues anchoring the two hemes on the cytoplasmic side and noncytoplasmic side of the
membrane are in all proteins located in the transmembrane helices 2, 4 and 3, 5, respectively. Several highly conserved amino
acids with aromatic side chain are identified between the two heme ligation sites. These residues may constitute a putative
transmembrane electron transport pathway. The present study demonstrates that the structural features in the cyt b
561 family are well conserved at both the sequence and the protein level. The central 4-helix core represents a transmembrane
electron transfer architecture that is highly conserved in eukaryotic species.
Received May 12, 2002; accepted September 20, 2002; published online May 21, 2003
RID="*"
ID="*" Correspondence and reprints: Institute of Biophysics, Biological Research Centre, P.O. Box 521, 6701 Szeged, Hungary.
E-mail: tpali@nucleus.szbk.u-szeged.hu 相似文献
9.
Able AJ 《Protoplasma》2003,221(1-2):137-143
Summary. The interactions between Hordeum vulgare (barley) and two fungal necrotrophs, Rhynchosporium secalis and Pyrenophora teres (causal agents of barley leaf scald and net blotch), were investigated in a detached-leaf system. An early oxidative burst
specific to epidermal cells was observed in both the susceptible and resistant responses to R. secalis, and later on, a second susceptible-specific burst was observed. Time points of the first and the second burst correlated
closely with pathogen contact to the plasma membrane and subsequent cell death, respectively. HO2
•/O2
− levels in resistant and susceptible responses to P. teres were limited in comparison. During later stages, HO2
•/O2
− was only detected in 2 to 3 epidermal cells immediately adjacent to phenolic browning and cell death observed during the
susceptible response. However, H2O2 was detected in the majority of mesophyll cells adjacent to the observed lesion caused by P. teres. In contrast to observations during challenge with R. secalis, no direct contact between P. teres and the plasma membrane at sites of reactive oxygen species production was evident. Preinfiltration of leaves with antioxidants
prior to challenge with either pathogen had no effect on resistance responses but did limit the growth of the pathogens and
inhibit the extent of cell death during susceptible responses. These results suggest a possible role for reactive oxygen species
in the induction of cell death during the challenge of a susceptible plant cell with a necrotrophic fungal leaf pathogen.
Received May 2, 2002; accepted July 26, 2002; published online May 21, 2003
RID="*"
ID="*" Correspondence and reprints: Department of Plant Science, Waite Campus PMB1, University of Adelaide, Glen Osmond, South
Australia 5064, Australia. 相似文献
10.
A mathematical model is developed with a highly controlled birth and death process for precursor cells. This model is both
biologically- and statistically-based. The controlled growth and differentiation (CGD) model limits the number of replications
allowed in the development of a tissue or organ and thus, more closely reflects the presence of a true stem cell population.
Leroux et al. (1996) presented a biologically-based dose-response model for developmental toxicology that was derived from a partial differential
equation for the generating function. This formulation limits further expansion into more realistic models of mammalian development.
The same formulae for the probability of a defect (a system of ordinary differential equations) can be derived through the
Kolmogorov forward equations due to the nature of this Markov process. This modified approach is easily amenable to the expansion
of more complicated models of the developmental process such as the one presented here. Comparisons between the Leroux et al. (1996) model and the controlled growth and differentiation (CGD) model as developed in this paper are also discussed.
Received: 8 June 2001 / Revised version: 15 June 2002 / Published online: 26 September 2002
Keywords or phrases: Teratology – Multistate process – Cellular kinetics – Numerical simulation 相似文献
11.
We examine a generalised SIR model for the infection dynamics of four competing disease strains. This model contains four
previously-studied models as special cases. The different strains interact indirectly by the mechanism of cross-immunity;
individuals in the host population may become immune to infection by a particular strain even if they have only been infected
with different but closely related strains. Several different models of cross-immunity are compared in the limit where the
death rate is much smaller than the rate of recovery from infection. In this limit an asymptotic analysis of the dynamics
of the models is possible, and we are able to compute the location and nature of the Takens–Bogdanov bifurcation associated
with the presence of oscillatory dynamics observed by previous authors.
Received: 5 December 2001 / Revised version: 5 May 2002 / Published online: 17 October 2002
Keywords or phrases: Infection – Pathogen – Epidemiology – Multiple strains – Cross-immunity – Oscillations – Dynamics – Bifurcations 相似文献
12.
We consider a two-dimensional model of cell-to-cell spread of HIV-1 in tissue cultures, assuming that infection is spread
directly from infected cells to healthy cells and neglecting the effects of free virus. The intracellular incubation period
is modeled by a gamma distribution and the model is a system of two differential equations with distributed delay, which includes
the differential equations model with a discrete delay and the ordinary differential equations model as special cases. We
study the stability in all three types of models. It is shown that the ODE model is globally stable while both delay models
exhibit Hopf bifurcations by using the (average) delay as a bifurcation parameter. The results indicate that, differing from
the cell-to-free virus spread models, the cell-to-cell spread models can produce infective oscillations in typical tissue
culture parameter regimes and the latently infected cells are instrumental in sustaining the infection. Our delayed cell-to-cell
models may be applicable to study other types of viral infections such as human T-cell leukaemia virus type 1 (HTLV-1).
Received: 18 November 2000 /
Published online: 28 February 2003
RID="*"
ID="*" Research was partially supported by the NSERC and MITACS of Canada and a start-up fund from the College of Arts and
Sciences at the University of Miami. On leave from Dalhousie University, Halifax, Nova Scotia, Canada.
Current address: Department of Mathematics, Clarke College, Dubuque, Iowa 52001, USA
Key words or phrases: HIV-1 – Cell-to-cell spread – Time delay – Stability – Hopf bifurcation – Periodicity 相似文献
13.
Ultrastructure of vascular cambial cell cytokinesis in pine seedlings preserved by cryofixation and substitution 总被引:4,自引:0,他引:4
Summary. Trees depend on the secondary vascular cambium to produce cells for new xylem and phloem. The fusiform cells of this lateral
meristem are long and narrow, presenting special challenges for arranging the mitotic spindle and phragmoplast. Fusiform cambial
cells of Pinus ponderosa and Pinus contorta were studied by cryofixation and cryosubstitution which preserved ultrastructure and phases of cytokinesis with a resolution
not previously attained. Membranous structures including the plasma membrane, tonoplast, and those of other organelles were
smooth and unbroken, indicating that they were preserved while the protoplasm was in a fully turgid state. Mitotic spindles
separated daughter chromosomes diagonally across the radial width of the cells. The cell plate was initiated at an angle to
the cell axis between the anaphase chromosomes by a microtubule array which organized vesicles at the phragmoplast midline.
Within the phragmoplast, vesicles initially joined across thin tubular projections and then amalgamated into a tubulo-vesicular
network. Axial expansion of the cell plate generated two opposing phragmoplasts connected by a thin, extended bridge of cell
plate and cytoplasm that was oriented along the cell axis. In the cytoplasmic bridge trailing each phragmoplast, the callose-rich
tubular network gradually consolidated into a fenestrated plate and then a complete cell wall. Where new membrane merged with
old, the parent plasmalemma appeared to be loosened from the cell wall and the membranes joined via a short tubulo-vesicular
network. These results have not been previously reported in cambial tissue, but the same phases of cytokinesis have been observed
in cryofixed root tips and suspension-cultured cells of tobacco.
Received February 11, 2002; accepted May 31, 2002; published online October 31, 2002
RID="*"
ID="*" Correspondence and reprints: Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver,
BC V6T 1Z4, Canada.
Abbreviations: CFS cryofixation and cryosubstitution; ER endoplasmic reticulum; HPF high-pressure freezing; PPB preprophase band. 相似文献
14.
Equations governing the transport of the gases oxygen and carbon dioxide inside the pulmonary capillaries are written down.
By analysing these equations it is predicted that there will be negligible limitation to the transport of oxygen when oxygen
concentration takes a normal physiological or higher value. For low values of oxygen concentration, there may be limitation
to oxygen transport. It is predicted further that the quantity of carbon dioxide excreted from blood into alveolar gas is
dependent on oxygen concentration, with low oxygen concentrations inhibiting the carbon dioxide transport process. The relatively
slow reaction involving carbon dioxide in plasma also inhibits the excretion of carbon dioxide. These predictions are verified
by solving the whole system of governing equations numerically.
Received: 1 May 2002 / Revised version: 20 October 2002 /
Published online: 19 March 2003
JPW was supported by a grant from the Engineering and Physical Sciences Research Council of Great Britain.
Key words or phrases: Pulmonary gas transport – Haemoglobin – Saturation 相似文献
15.
Summary. Recently, p210 was identified as a component of the flagellar basal apparatus in the green flagellate Spermatozopsis similis. In a search for potential homologues to p210, isolated cytoskeletons of several green flagellates were probed with a monoclonal
antibody, BAS4.13, against p210. In Western blots, cross-reacting bands in the molecular-mass range of 210 kDa were detected
only in the quadriflagellate Spermatozopsis exsultans. As described earlier for S. similis, the flagellar transition region was decorated in Chlamydomonas reinhardtii and several other green flagellates, whereas in the marine alga Dunaliella bioculata the antigen was present in the proximal part of the axoneme. Double immunofluorescence of D. bioculata with an antitubulin antibody further revealed dotlike signals at sites where the probasal bodies are located. Since most
of the antigen in D. bioculata was located in the axoneme, deflagellation offered a possibility to study the kinetics of its incorporation during flagellar
regeneration. The antigen was only detected after a flagellum reached a length of 3–4 μm and its integration into the growing
flagellar proceeded from proximal to distal. A similar delay in the incorporation of the antigen was also observed during
flagellar assembly on new basal bodies during cell division. Thus, the antigen of BAS4.13 was incorporated late and from proximal
to distal into the growing flagellum. We conclude that the pace and site by which individual proteins are integrated into
the flagellum differ greatly.
Received February 18, 2002; accepted May 17, 2002; published on line October 31, 2002
RID="*"
ID="*" Correspondence and reprints: Botanisches Institut, Universit?t zu K?ln, Gyrhofstrasse 15, 50931 K?ln, Federal Republic
of Germany 相似文献
16.
Summary. This study investigates the relationship between changes in plasma sodium and changes in amino acid levels in a patient with
post-traumatic sepsis and prolonged critical illness. Ninety-two consecutive measurements were performed at regular intervals
over a period of many weeks; these consisted in the determination of full amino-acidograms, plasma sodium and complementary
variables. A unique, highly significant inverse correlation between taurine and plasma sodium was found (r2 = 0.48, p < 0.001). All other amino acids were unrelated, or much more weakly related, to sodium. Taurine was also strongly
and directly related to phosphoethanolamine, glutamate and aspartate. Changes in sodium and in levels of these amino acids
explained up to 86% of the variability of taurine. Besides, levels of these amino acids maintained a high degree of co-variation,
remaining reciprocally related one to each other, directly, with r2 ranging between 0.33 and 0.59 (p < 0.001 for all). There were similar findings for β-alanine, which however was measured inconsistently. These data provide gross clinical evidence of a specific link binding
plasma sodium and taurine levels, and may be consistent with occurrence of opposite and interdependent shifts of sodium and
taurine between intravascular and extravascular space, to maintain osmoregulation. Co-variation of taurine with the other
amino acids may be related to the same phenomenon, and/or to similarities in transport systems and chemical structure, or
true metabolic interactions.
Received April 16, 2002 Accepted June 19, 2002 Published online November 14, 2002
RID="*"
ID="*" Presented at the 7th International Congress on Amino Acids and Proteins, Vienna (Austria), August 6–10, 2001.
Acknowledgements The authors acknowledge the kind assistance of Mr. Maurizio Cianfanelli, from the Catholic University School of Medicine,
Rome, Italy.
Authors' address: Dr. Carlo Chiarla, Via Augusto Tebaldi, 19, I-00168 Roma, Italy, E-mail: carlo.chiarla@rm.unicatt.it 相似文献
17.
Summary. The aim of this work was to study the activity of NAD(P)H:(quinone acceptor) oxidoreductase 1 (EC 1.6.99.2) in the regeneration
of lipophilic antioxidants, alpha-tocopherol, and reduced-coenzyme Q analogs. First, we tested whether or not two isoforms
of the NAD(P)H:(quinone acceptor) oxidoreductase 1 designated as “hydrophilic” and “hydrophobic” (H. J. Prochaska and P. Talalay,
Journal of Biological Chemistry 261: 1372–1378, 1986) show differential enzyme activities towards hydrophilic or hydrophobic
ubiquinone homologs. By chromatography on phenyl Sepharose, we purified the two isoforms from pig liver cytosol and measured
their reduction of several ubiquinone homologs of different side chain length. We also studied by electron paramagnetic resonance
the effect of NAD(P)H:(quinone acceptor) oxidoreductase 1 on steady-state levels of chromanoxyl radicals generated by linoleic
acid and lipooxygenase and confirmed the enzyme's ability to protect alpha-tocopherol against oxidation induced with H2O2-Fe2+. Our results demonstrated that the different hydrophobicities of the isoforms do not reflect different reactivities towards
ubiquinones of different side chain length. In addition, electron paramagnetic resonance studies showed that in systems containing
the reductase plus NADH, levels of chromanoxyl radicals were dramatically reduced. Morever, in the presence of oxidants, alpha-tocopherol
was preserved by NAD(P)H:(quinone acceptor) oxidoreductase 1, supporting our hypothesis that regeneration of alpha-tocopherol
may be one of the physiologic functions of this enzyme.
Received May 20, 2002; accepted September 20, 2002; published online May 21, 2003
RID="*"
ID="*" Correspondence and reprints: Departamento de Biología Celular, Fisiología e Inmunología, Facultad de Ciencias, Edificio
Severo Ochoa, Campus de Rabanales, Universidad de Córdoba, 14014 Córdoba, Spain. 相似文献
18.
We consider a partially coupled diffusive population model in which the state variables represent the densities of the immature
and mature population of a single species. The equation for the mature population can be considered on its own, and is a delay
differential equation with a delay-dependent coefficient. For the case when the immatures are immobile, we prove that travelling
wavefront solutions exist connecting the zero solution of the equation for the matures with the delay-dependent positive equilibrium
state. As a perturbation of this case we then consider the case of low immature diffusivity showing that the travelling front
solutions continue to persist. Our findings are contrasted with recent studies of the delayed Fisher equation. Travelling
fronts of the latter are known to lose monotonicity for sufficiently large delays. In contrast, travelling fronts of our equation
appear to remain monotone for all values of the delay.
Received: 1 November 2001 / Revised version: 10 May 2002 / Published online: 23 August 2002
Mathematics Subject Classification (2000): 35K57, 92D25
Key words or phrases: Age-structure – Time-delay – Travelling Fronts – Reaction-diffusion 相似文献
19.
Localization of sucrose synthase and callose in freeze-substituted secondary-wall-stage cotton fibers 总被引:2,自引:0,他引:2
Summary. Methods for cryogenic fixation, freeze substitution, and embedding were developed to preserve the cellular structure and
protein localization of secondary-wall-stage cotton (Gossypium hirsutum L.) fibers accurately for the first time. Perturbation by specimen handling was minimized by freezing fibers still attached
to a seed fragment within 2 min after removal of seeds from a boll still attached to the plant. These methods revealed native
ultrastructure, including numerous active Golgi bodies, multivesicular bodies, and proplastids. Immunolocalization in the
context of accurate structure was accomplished after freeze substitution in acetone only. Quantitation of immunolabeling identified
sucrose synthase both near the cortical microtubules and plasma membrane and in a proximal exoplasmic zone about 0.2 μm thick.
Immunolabeling also showed that callose (β-1,3-glucan) was codistributed with sucrose synthase within this exoplasmic zone.
Similar results were obtained from cultured cotton fibers. The distribution of sucrose synthase is consistent with its having
a dual role in cellulose and callose synthesis in secondary-wall-stage cotton fibers.
Received August 19, 2002; accepted November 12, 2002; published online June 13, 2003
RID="*"
ID="*" Correspondence and reprints: Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409-3131, U.S.A.
E-mail: candace.haigler@ttu.edu 相似文献
20.
Summary. In eudicot postmeiotic tetrads, apertures are usually joined in pairs in highly conserved areas. These appear to be located
at the last points of contact persisting at the end of cytokinesis between the cytoplasm of the future microspores. In order
to investigate the relationship between cytokinesis and aperture formation, aperture distribution within postmeiotic tetrads
and the progression of meiosis were studied in Nicotiana tabacum cv. Ambalema. This variety (inbred line) produces about 85% tricolporate pollen and 15% tetracolporate pollen grains. In
addition, about 7% of tetrads are composed of four equal-sized microspores and a supernumerary pseudomicrospore of small size
and an equal proportion of tetrads exhibit unpaired apertures (these apertures are not joined in pairs within tetrads). Observation
of cytokinesis indicates that both unpaired apertures and pseudomicrospores could result from the persistence of late communications
between microsporocytes. Observations of tetrads indicate that an increase in the number of elements that are separated during
cytokinesis is correlated with an increase in microspore aperture number. All data converge to support the hypothesis that
aperture site determination is partly controlled by the number of walls formed to separate the different elements of the tetrad.
Received May 22, 2002; accepted October 29, 2002; published online April 2, 2003
RID="*"
ID="*" Correspondence and reprints: Laboratoire de Ecologie, Systematique et Evolution, Batiment 362, Université Paris Sud,
91405 Orsay cedex, France. 相似文献