Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 20 de 20
Filter
Add more filters










Publication year range
1.
Science ; 299(5615): 2071-4, 2003 Mar 28.
Article in English | MEDLINE | ID: mdl-12663927

ABSTRACT

The complete genome sequence of Enterococcus faecalis V583, a vancomycin-resistant clinical isolate, revealed that more than a quarter of the genome consists of probable mobile or foreign DNA. One of the predicted mobile elements is a previously unknown vanB vancomycin-resistance conjugative transposon. Three plasmids were identified, including two pheromone-sensing conjugative plasmids, one encoding a previously undescribed pheromone inhibitor. The apparent propensity for the incorporation of mobile elements probably contributed to the rapid acquisition and dissemination of drug resistance in the enterococci.


Subject(s)
Biological Evolution , Enterococcus faecalis/genetics , Genome, Bacterial , Interspersed Repetitive Sequences , Sequence Analysis, DNA , Vancomycin Resistance/genetics , Adhesins, Bacterial/genetics , Bacterial Adhesion , Bacterial Proteins/genetics , Carrier Proteins/genetics , Carrier Proteins/metabolism , Chromosomes, Bacterial/genetics , Conjugation, Genetic , Conserved Sequence , DNA Transposable Elements , Digestive System/microbiology , Drug Resistance, Multiple, Bacterial , Enterococcus faecalis/drug effects , Enterococcus faecalis/pathogenicity , Enterococcus faecalis/physiology , Gene Transfer, Horizontal , Gram-Positive Bacterial Infections/microbiology , Humans , Lysogeny , Open Reading Frames , Oxidative Stress , Plasmids , Synteny , Virulence/genetics , Virulence Factors/genetics
2.
Emerg Infect Dis ; 6(5): 505-12, 2000.
Article in English | MEDLINE | ID: mdl-10998382

ABSTRACT

The sequences of close to 30 microbial genomes have been completed during the past 5 years, and the sequences of more than 100 genomes should be completed in the next 2 to 4 years. Soon, completed microbial genome sequences will represent a collection of >200,000 predicted coding sequences. While analysis of a single genome provides tremendous biological insights on any given organism, comparative analysis of multiple genomes provides substantially more information on the physiology and evolution of microbial species and expands our ability to better assign putative function to predicted coding sequences.


Subject(s)
Bacteria/genetics , Evolution, Molecular , Genome, Archaeal , Genome, Bacterial , Genomics/methods , Bacteria/pathogenicity , Carrier Proteins/genetics , Humans , Sequence Analysis
3.
Science ; 287(5459): 1809-15, 2000 Mar 10.
Article in English | MEDLINE | ID: mdl-10710307

ABSTRACT

The 2,272,351-base pair genome of Neisseria meningitidis strain MC58 (serogroup B), a causative agent of meningitis and septicemia, contains 2158 predicted coding regions, 1158 (53.7%) of which were assigned a biological role. Three major islands of horizontal DNA transfer were identified; two of these contain genes encoding proteins involved in pathogenicity, and the third island contains coding sequences only for hypothetical proteins. Insights into the commensal and virulence behavior of N. meningitidis can be gleaned from the genome, in which sequences for structural proteins of the pilus are clustered and several coding regions unique to serogroup B capsular polysaccharide synthesis can be identified. Finally, N. meningitidis contains more genes that undergo phase variation than any pathogen studied to date, a mechanism that controls their expression and contributes to the evasion of the host immune system.


Subject(s)
Genome, Bacterial , Neisseria meningitidis/genetics , Neisseria meningitidis/pathogenicity , Sequence Analysis, DNA , Antigenic Variation , Antigens, Bacterial/immunology , Bacteremia/microbiology , Bacterial Capsules/genetics , Bacterial Proteins/genetics , Bacterial Proteins/physiology , DNA Transposable Elements , Evolution, Molecular , Fimbriae, Bacterial/genetics , Humans , Meningitis, Meningococcal/microbiology , Meningococcal Infections/microbiology , Molecular Sequence Data , Mutation , Neisseria meningitidis/classification , Neisseria meningitidis/physiology , Open Reading Frames , Operon , Phylogeny , Recombination, Genetic , Serotyping , Transformation, Bacterial , Virulence/genetics
4.
Science ; 286(5444): 1571-7, 1999 Nov 19.
Article in English | MEDLINE | ID: mdl-10567266

ABSTRACT

The complete genome sequence of the radiation-resistant bacterium Deinococcus radiodurans R1 is composed of two chromosomes (2,648,638 and 412,348 base pairs), a megaplasmid (177,466 base pairs), and a small plasmid (45,704 base pairs), yielding a total genome of 3,284, 156 base pairs. Multiple components distributed on the chromosomes and megaplasmid that contribute to the ability of D. radiodurans to survive under conditions of starvation, oxidative stress, and high amounts of DNA damage were identified. Deinococcus radiodurans represents an organism in which all systems for DNA repair, DNA damage export, desiccation and starvation recovery, and genetic redundancy are present in one cell.


Subject(s)
Genome, Bacterial , Gram-Positive Cocci/genetics , Physical Chromosome Mapping , Sequence Analysis, DNA , Bacterial Proteins/biosynthesis , Bacterial Proteins/chemistry , Bacterial Proteins/genetics , Catalase/genetics , Chromosomes, Bacterial/genetics , DNA Damage , DNA Repair/genetics , DNA, Bacterial/genetics , Energy Metabolism , Genes, Bacterial , Gram-Positive Cocci/chemistry , Gram-Positive Cocci/classification , Gram-Positive Cocci/radiation effects , Molecular Sequence Data , Open Reading Frames , Oxidative Stress , Plasmids , Radiation Tolerance , Repetitive Sequences, Nucleic Acid , Superoxide Dismutase/genetics , Thermus/chemistry , Thermus/genetics , Ultraviolet Rays
5.
Proc Natl Acad Sci U S A ; 96(13): 7581-6, 1999 Jun 22.
Article in English | MEDLINE | ID: mdl-10377458

ABSTRACT

The potassium-channel gene, AKT3, has recently been isolated from an Arabidopsis thaliana cDNA library. By using the whole-mount and in situ hybridization techniques, we found AKT3 predominantly expressed in the phloem. To study the physiological role of this channel type, AKT3 was heterologously expressed in Xenopus oocytes, and the electrical properties were examined with voltage-clamp techniques. Unlike the plant inward-rectifying guard cell K+ channels KAT1 and KST1, the AKT3 channels were only weakly regulated by the membrane potential. Furthermore, AKT3 was blocked by physiological concentrations of external Ca2+ and showed an inverted pH regulation. Extracellular acidification decreased the macroscopic AKT3 currents by reducing the single-channel conductance. Because assimilate transport in the vascular tissue coincides with both H+ and K+ fluxes, AKT3 K+ channels may be involved in K+ transport accompanying phloem loading and unloading processes.


Subject(s)
Arabidopsis/physiology , Potassium Channels/physiology , Electrophysiology , Genes, Plant , Ion Channel Gating , Plant Proteins/physiology , Protons
6.
Nature ; 399(6734): 323-9, 1999 May 27.
Article in English | MEDLINE | ID: mdl-10360571

ABSTRACT

The 1,860,725-base-pair genome of Thermotoga maritima MSB8 contains 1,877 predicted coding regions, 1,014 (54%) of which have functional assignments and 863 (46%) of which are of unknown function. Genome analysis reveals numerous pathways involved in degradation of sugars and plant polysaccharides, and 108 genes that have orthologues only in the genomes of other thermophilic Eubacteria and Archaea. Of the Eubacteria sequenced to date, T. maritima has the highest percentage (24%) of genes that are most similar to archaeal genes. Eighty-one archaeal-like genes are clustered in 15 regions of the T. maritima genome that range in size from 4 to 20 kilobases. Conservation of gene order between T. maritima and Archaea in many of the clustered regions suggests that lateral gene transfer may have occurred between thermophilic Eubacteria and Archaea.


Subject(s)
Archaea/genetics , Genome, Bacterial , Recombination, Genetic , Thermotoga maritima/genetics , Bacterial Proteins/metabolism , DNA, Bacterial , Genes, Archaeal , Molecular Sequence Data , Multigene Family , Open Reading Frames , Phylogeny , Protein Biosynthesis , Sequence Analysis, DNA , Thermotoga maritima/classification , Thermotoga maritima/physiology , Transcription, Genetic , Transformation, Bacterial
7.
Nature ; 402(6763): 761-8, 1999 Dec 16.
Article in English | MEDLINE | ID: mdl-10617197

ABSTRACT

Arabidopsis thaliana (Arabidopsis) is unique among plant model organisms in having a small genome (130-140 Mb), excellent physical and genetic maps, and little repetitive DNA. Here we report the sequence of chromosome 2 from the Columbia ecotype in two gap-free assemblies (contigs) of 3.6 and 16 megabases (Mb). The latter represents the longest published stretch of uninterrupted DNA sequence assembled from any organism to date. Chromosome 2 represents 15% of the genome and encodes 4,037 genes, 49% of which have no predicted function. Roughly 250 tandem gene duplications were found in addition to large-scale duplications of about 0.5 and 4.5 Mb between chromosomes 2 and 1 and between chromosomes 2 and 4, respectively. Sequencing of nearly 2 Mb within the genetically defined centromere revealed a low density of recognizable genes, and a high density and diverse range of vestigial and presumably inactive mobile elements. More unexpected is what appears to be a recent insertion of a continuous stretch of 75% of the mitochondrial genome into chromosome 2.


Subject(s)
Arabidopsis/genetics , Chromosome Mapping , DNA, Plant , Genes, Plant , Cell Nucleus/genetics , Centromere , Evolution, Molecular , Gene Duplication , Genes, Plant/physiology , Mitochondria/genetics , Molecular Sequence Data , Plant Proteins/genetics , Plant Proteins/physiology , Sequence Analysis, DNA
8.
Science ; 281(5375): 375-88, 1998 Jul 17.
Article in English | MEDLINE | ID: mdl-9665876

ABSTRACT

The complete genome sequence of Treponema pallidum was determined and shown to be 1,138,006 base pairs containing 1041 predicted coding sequences (open reading frames). Systems for DNA replication, transcription, translation, and repair are intact, but catabolic and biosynthetic activities are minimized. The number of identifiable transporters is small, and no phosphoenolpyruvate:phosphotransferase carbohydrate transporters were found. Potential virulence factors include a family of 12 potential membrane proteins and several putative hemolysins. Comparison of the T. pallidum genome sequence with that of another pathogenic spirochete, Borrelia burgdorferi, the agent of Lyme disease, identified unique and common genes and substantiates the considerable diversity observed among pathogenic spirochetes.


Subject(s)
Genome, Bacterial , Sequence Analysis, DNA , Treponema pallidum/genetics , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Base Sequence , Borrelia burgdorferi Group/genetics , Carrier Proteins/genetics , Carrier Proteins/metabolism , DNA Repair/genetics , DNA Replication/genetics , DNA Restriction Enzymes/genetics , Energy Metabolism/genetics , Genes, Bacterial , Genes, Regulator , Heat-Shock Response/genetics , Lipoproteins/genetics , Membrane Proteins/genetics , Molecular Sequence Data , Movement , Open Reading Frames , Oxygen Consumption/genetics , Protein Biosynthesis , Recombination, Genetic , Replication Origin , Transcription, Genetic , Treponema pallidum/metabolism , Treponema pallidum/pathogenicity
9.
Curr Opin Plant Biol ; 1(2): 136-41, 1998 Apr.
Article in English | MEDLINE | ID: mdl-10066574

ABSTRACT

The large number of ESTs generated for Arabidopsis and rice in recent years now act as an important complement to whole genome sequencing projects. The Arabidopsis Genome Initiative has begun a coordinated effort to sequence the entire genome and, as a result, increasing numbers of large sequence entries can be found in the public databases. In addition, the mitochondrial genome of Arabidopsis has been completely sequenced. Genome sequencing studies and the public sequence databases have begun to influence the direction of diverse areas of research from physiology to evolution.


Subject(s)
DNA, Plant/chemistry , Expressed Sequence Tags , Genome, Plant , Base Sequence , Molecular Sequence Data , Multigene Family , Sequence Analysis, DNA
10.
Nature ; 390(6660): 580-6, 1997 Dec 11.
Article in English | MEDLINE | ID: mdl-9403685

ABSTRACT

The genome of the bacterium Borrelia burgdorferi B31, the aetiologic agent of Lyme disease, contains a linear chromosome of 910,725 base pairs and at least 17 linear and circular plasmids with a combined size of more than 533,000 base pairs. The chromosome contains 853 genes encoding a basic set of proteins for DNA replication, transcription, translation, solute transport and energy metabolism, but, like Mycoplasma genitalium, it contains no genes for cellular biosynthetic reactions. Because B. burgdorferi and M. genitalium are distantly related eubacteria, we suggest that their limited metabolic capacities reflect convergent evolution by gene loss from more metabolically competent progenitors. Of 430 genes on 11 plasmids, most have no known biological function; 39% of plasmid genes are paralogues that form 47 gene families. The biological significance of the multiple plasmid-encoded genes is not clear, although they may be involved in antigenic variation or immune evasion.


Subject(s)
Borrelia burgdorferi Group/genetics , Genome, Bacterial , Biological Transport , Chemotaxis , Chromosomes, Bacterial , DNA Repair , DNA, Bacterial/biosynthesis , DNA, Bacterial/genetics , Energy Metabolism , Gene Expression Regulation, Bacterial , Lyme Disease/microbiology , Membrane Proteins/genetics , Molecular Sequence Data , Plasmids , Protein Biosynthesis , Recombination, Genetic , Replication Origin , Telomere , Transcription, Genetic
11.
Nature ; 390(6658): 364-70, 1997 Nov 27.
Article in English | MEDLINE | ID: mdl-9389475

ABSTRACT

Archaeoglobus fulgidus is the first sulphur-metabolizing organism to have its genome sequence determined. Its genome of 2,178,400 base pairs contains 2,436 open reading frames (ORFs). The information processing systems and the biosynthetic pathways for essential components (nucleotides, amino acids and cofactors) have extensive correlation with their counterparts in the archaeon Methanococcus jannaschii. The genomes of these two Archaea indicate dramatic differences in the way these organisms sense their environment, perform regulatory and transport functions, and gain energy. In contrast to M. jannaschii, A. fulgidus has fewer restriction-modification systems, and none of its genes appears to contain inteins. A quarter (651 ORFs) of the A. fulgidus genome encodes functionally uncharacterized yet conserved proteins, two-thirds of which are shared with M. jannaschii (428 ORFs). Another quarter of the genome encodes new proteins indicating substantial archaeal gene diversity.


Subject(s)
Archaeoglobus fulgidus/genetics , Genes, Archaeal , Genome , Archaeoglobus fulgidus/metabolism , Archaeoglobus fulgidus/physiology , Base Sequence , Cell Division , DNA, Bacterial/genetics , Energy Metabolism , Gene Expression Regulation, Bacterial , Molecular Sequence Data , Protein Biosynthesis , Transcription, Genetic
12.
Nature ; 388(6642): 539-47, 1997 Aug 07.
Article in English | MEDLINE | ID: mdl-9252185

ABSTRACT

Helicobacter pylori, strain 26695, has a circular genome of 1,667,867 base pairs and 1,590 predicted coding sequences. Sequence analysis indicates that H. pylori has well-developed systems for motility, for scavenging iron, and for DNA restriction and modification. Many putative adhesins, lipoproteins and other outer membrane proteins were identified, underscoring the potential complexity of host-pathogen interaction. Based on the large number of sequence-related genes encoding outer membrane proteins and the presence of homopolymeric tracts and dinucleotide repeats in coding sequences, H. pylori, like several other mucosal pathogens, probably uses recombination and slipped-strand mispairing within repeats as mechanisms for antigenic variation and adaptive evolution. Consistent with its restricted niche, H. pylori has a few regulatory networks, and a limited metabolic repertoire and biosynthetic capacity. Its survival in acid conditions depends, in part, on its ability to establish a positive inside-membrane potential in low pH.


Subject(s)
Genome, Bacterial , Helicobacter pylori/genetics , Antigenic Variation , Bacterial Adhesion , Bacterial Proteins/metabolism , Base Sequence , Biological Evolution , Cell Division , DNA Repair , DNA, Bacterial/genetics , Gene Expression Regulation, Bacterial , Helicobacter pylori/metabolism , Helicobacter pylori/pathogenicity , Hydrogen-Ion Concentration , Molecular Sequence Data , Protein Biosynthesis , Recombination, Genetic , Transcription, Genetic , Virulence
14.
FEBS Lett ; 378(1): 19-26, 1996 Jan 02.
Article in English | MEDLINE | ID: mdl-8549795

ABSTRACT

A degenerate oligonucleotide corresponding to the K+ channel signature sequence (TMTTVGYGD) was used to isolate the genomic and cDNA forms of a new channel gene, AKT3, from Arabidopsis thaliana. The deduced protein sequence has a predicted membrane topography similar to Shaker-like K+ channels. Three distinct modules comprise the carboxyl-terminal half: a nucleotide-binding motif, an ankyrin repeat domain, and a polyglutamate track. Xenopus oocytes injected with cRNA exhibited an inward-rectifying K+ current, demonstrating that the AKT3 polypeptide is a functional transport protein. Two other Arabidopsis K+ transporters (AKT1 and KAT1) share 60% homology with AKT3; together these proteins constitute a family of plant inward-rectifying K+ channels.


Subject(s)
Arabidopsis/genetics , DNA, Plant/isolation & purification , Potassium Channels/genetics , Amino Acid Sequence , Animals , Base Sequence , Binding Sites , Blotting, Southern , DNA, Complementary/chemistry , DNA, Complementary/isolation & purification , DNA, Plant/chemistry , DNA, Plant/metabolism , Female , Gene Expression , Introns , Molecular Sequence Data , Oocytes/metabolism , Potassium Channels/chemistry , Potassium Channels/metabolism , Repetitive Sequences, Nucleic Acid , Sequence Alignment , Transfection , Xenopus laevis
15.
Nature ; 376(6542): 690-5, 1995 Aug 24.
Article in English | MEDLINE | ID: mdl-7651518

ABSTRACT

Potassium channels catalyse the permeation of K+ ions across cellular membranes and are identified by a common structural motif, a highly conserved signature sequence of eight amino acids in the P domain of each channel's pore-forming alpha-subunit. Here we describe a novel K+ channel (TOK1) from Saccharomyces cerevisiae that contains two P domains within one continuous polypeptide. Xenopus laevis oocytes expressing the channel exhibit a unique, outwardly rectifying, K(+)-selective current. The channel is permeable to outward flow of ions at membrane potentials above the K+ equilibrium potential; its conduction-voltage relationship is thus sensitive to extracellular K+ ion concentration. In excised membrane patches, external divalent cations block the channel in a voltage-dependent manner, and their removal in this configuration allows inward channel current. These attributes are similar to those described for inwardly rectifying K+ channels, but in the opposite direction, a previously unrecognized channel behaviour. Our results identify a new class of K+ channel which is distinctive in both its primary structure and functional properties. Structural homologues of the channel are present in the genome of Caenorhabditis elegans.


Subject(s)
Potassium Channels/metabolism , Saccharomyces cerevisiae Proteins , Saccharomyces cerevisiae/metabolism , Amino Acid Sequence , Animals , Base Sequence , Caenorhabditis elegans , Cells, Cultured , DNA Primers , Drosophila , Molecular Sequence Data , Oocytes , Patch-Clamp Techniques , Potassium/metabolism , Potassium Channels/chemistry , Potassium Channels/genetics , Protein Conformation , Recombinant Proteins , Sequence Homology, Amino Acid , Sodium/metabolism , Xenopus laevis
16.
J Membr Biol ; 119(3): 277-88, 1991 Feb.
Article in English | MEDLINE | ID: mdl-1647462

ABSTRACT

The voltage- and time-dependent K+ current, IK+ out, elicited by depolarization of corn protoplasts, was inhibited by the addition of calcium channel antagonists (nitrendipine, nifedipine, verapamil, methoxyverapamil, bepridil, but not La3+) to the extracellular medium. These results suggested that the influx of external Ca2+ was necessary for K+ current activation. The IC50, concentration of inhibitor that caused 50% reduction of the current, for nitrendipine was 1 microM at a test potential of +60 mV following a 20-min incubation period. In order to test whether intracellular Ca2+ actuated the K+ current, we altered either the Ca2+ buffering capacity or the free Ca2+ concentration of the intracellular medium (pipette filling solution). By these means, IK+out could be varied over a 10-fold range. Increasing the free Ca2+ concentration from 40 to 400 nM also shifted the activation of the K+ current toward more negative potentials. Maintaining cytoplasmic Ca2+ at 500 nM with 40 nM EGTA resulted in a more rapid activation of the K+ current. Thus the normal rate of activation of this current may reflect changes in cytoplasmic Ca2+ on depolarization. Increasing intracellular Ca2+ to 500 nM or 1 microM also led to inactivation of the K+ current within a few minutes. It is concluded that IK+out is regulated by cytosolic Ca2+, which is in turn controlled by Ca2+ influx through dihydropyridine-, and phenylalkylamine-sensitive channels.


Subject(s)
Calcium Channel Blockers/pharmacology , Calcium/metabolism , Plants/metabolism , Potassium/metabolism , Biological Transport, Active , Calcium Channels/metabolism , Cells, Cultured , Cytosol/physiology , Dihydropyridines/chemistry , Isotopes , Lanthanum , Membrane Potentials , Protoplasts/metabolism , Zea mays
17.
FEBS Lett ; 274(1-2): 115-8, 1990 Nov 12.
Article in English | MEDLINE | ID: mdl-1701395

ABSTRACT

We investigated the sensitivity of the Ca2(+)-dependent K+ current, IK(Ca), present in corn protoplasts, to different K+ channel blockers. IK(Ca) was inhibited by external Cs+ (10 mM), Ba2+ (10 mM), and quinine (0.5 mM): reagents which block many types of outward-rectifying K+ channels. In contrast 4-aminopyridine (5 mM), an inhibitor of delayed rectifier or inactivating K+ currents, had no effect. Neither of the peptide toxins, apamin or charybdotoxin, specific for Ca2(+)-dependent K+ channels in animal cells, inhibited currents when used in the nanomolar concentration range. However, higher levels of charybdotoxin (10 microM) caused marked reduction of IK(Ca).


Subject(s)
Barium Compounds , Calcium/pharmacology , Chlorides , Potassium Channels/physiology , Zea mays/physiology , Barium/pharmacology , Cesium/pharmacology , Charybdotoxin , Membrane Potentials/drug effects , Plant Physiological Phenomena , Potassium Channels/drug effects , Protoplasts/physiology , Quinine/pharmacology , Scorpion Venoms/pharmacology
18.
Plant Physiol ; 89(4): 1184-92, 1989 Apr.
Article in English | MEDLINE | ID: mdl-16666682

ABSTRACT

Protoplasts obtained from corn (Zea mays) suspension cells were studied using the whole cell patch-clamp technique. One time-independent current, as well as two time-dependent currents were identified. All three currents were reduced by tetraethylammonium (9 millimolar), a K(+) channel blocker. The time-independent current had a nearly linear current-voltage relationship and its reversal potential, defined as the voltage at which there is zero current, was highly dependent on the extracellular potassium concentration. One of the two time-dependent currents was activated, with rapid kinetics, by membrane hyperpolarization to potentials more negative than -100 millivolts. The second time-dependent current was activated with a sigmoidal time course by membrane depolarization to potentials more positive than -60 millivolts. It exhibited no inactivation and was carried primarily by potassium ions. These characteristics suggest that this latter current is caused by the voltage-dependent opening of delayed-rectifier K(+) channels. These three currents, which are not generated by the plasmalemma H(+)-ATPase, are likely to assist in the regulation of the cellular K(+) fluxes and membrane potential.

19.
Plant Physiol ; 87(1): 69-77, 1988 May.
Article in English | MEDLINE | ID: mdl-16666129

ABSTRACT

Fern (Onoclea sensibilis L.) gametophytes exposed to blue light are induced to undergo a morphological transition from a tip-growing filament to a planar prothallus. Extracellular measurements of electric currents and localized ion activities around the apical cell of 8 to 10 day-old gametophytes were made with a vibrating probe and ion selective electrodes. In darkness, we observed exit current densities of an average of 75 nanoamperes per square centimeter near the tip and 2 to 15 nanoamperes per square centimeter along the lateral walls of this cell. Measurements with ion selective electrodes for H(+), K(+), and Ca(2+) showed that this cell was bounded by a thin layer of medium that was depleted in K(+) and Ca(2+) and exhibited a lower pH than the bulk solution. Both the K(+) and Ca(2+) depletion zones and the zone of higher acidity were particularly pronounced at the tip end of the cell; the pH at 2 micrometers from the tip was nearly 0.5 units more acid than the bulk medium at pH 6. Disruption of steady state, external gradients with media that contained lower concentrations of H(+), K(+), Ca(2+), or Cl(-) produced certain differences in the rates of restoration of particular ion zones, raising the possibility that some of the ion migrations are interdependent. Within 15 minutes after irradiation with blue light, current leaving the tip declined to levels which were indistinguishable from those leaving the lateral walls and there was a rapid lowering in the rates of tip acidification and K(+) depletion near the tip. The rapid dissipation of both the longitudinally aligned electrical field and the tip-localized asymmetries in external cation distribution in blue light suggest that loss of electrical polarity in this tip growing cell may be an initial step in the chain of events which govern changes in cell shape.

SELECTION OF CITATIONS
SEARCH DETAIL
...