RESUMO
Circadian rhythms have formed the subject of many researches in man during bed rest or usual routine, but have been little studied during continuous and sustained physical exercise. This study deals with the influence of time of day on biological markers in competitive cyclists during continuous physical exercise versus continuous rest. Ultra-distance cyclists were studied over a 24 h period (13:00 to 13:00 h the next day) in the laboratory. The subjects were requested to maintain a constant speed (set at 65% - 70% of their maximal aerobic speed obtained during a preliminary test) on their own bicycles which were equipped with home trainers. Workload, core temperature and heart rate were monitored continuously. The same measures were also recorded while the athletes were resting awake until 13:00 h the next day. Results show that in both situations, core temperature and heart rate exhibited significant circadian variations (p < 0.001). Furthermore, during exercise, an accentuation of amplitude and mean of every rhythm (p < 0.05) with a phase lag (p < 0.05) were observed. Despite a strenuous and continuous physical exercise requiring special physiological adaptations, the rhythmic variations observed at rest persisted, which highlighted the influence of biological clocks.
Assuntos
Temperatura Corporal/fisiologia , Ritmo Circadiano/fisiologia , Frequência Cardíaca/fisiologia , Resistência Física/fisiologia , Adulto , Análise de Variância , Ciclismo/fisiologia , Exercício Físico , Humanos , Masculino , DescansoRESUMO
This study deals with the influence of time of day on neuromuscular efficiency in competitive cyclists during continuous exercise versus continuous rest. Knee extension torque was measured in ultradistance cyclists over a 24h period (13:00 to 13:00 the next day) in the laboratory. The subjects were requested to maintain a constant speed (set at 70% of their maximal aerobic speed obtained during a preliminary test) on their own bicycles, which were equipped with cyclosimulators. Every 4h, torque developed and myoelectric activity were estimated during maximal isometric voluntary contractions of knee extensors using an isokinetic dynamometer. Mesenteric temperature was monitored by telemetry. The same measures were also recorded while the subjects were resting awake until 13:00 the next day. During activity, torque changed within the 24h period (p < .005), with an acrophase at 19:10 and an amplitude of 7.8% around the mean of 70.7%. At rest, a circadian rhythm was observed in knee extensor torque (p < .05), with an acrophase at 19:30 and an amplitude of 6% around the mean of 92.3%. Despite the standardized conditions, the results showed that isometric maximal strength varied with time of day during both a submaximal exercise and at rest without prior exercise. The sine waves representing these two rhythms were correlated significantly. Although at rest the diurnal rhythm followed muscular activity (i.e., neurophysiological factors), during exercise, this rhythm was thought to stem more from fluctuations in the contractile state of muscle.
Assuntos
Ritmo Circadiano/fisiologia , Exercício Físico/fisiologia , Contração Isométrica/fisiologia , Adulto , Ciclismo/fisiologia , Temperatura Corporal/fisiologia , Estudos Cross-Over , Humanos , Masculino , Fadiga Muscular/fisiologia , Descanso/fisiologiaRESUMO
The influence of time of day on muscular performance was studied. From part of the results of two different studies (EAS et EPS), the effects of sleep deprivation were appreciated. Seven times over the 24-h period, developed torque and myoelectric activity were estimated during maximal isometric voluntary contractions using an isokinetic dynamometer: elbow flexion for EAS in standardised sleep, and knee extension for EPS in complete sleep deprivation. The results showed nycthemeral changes in torque in both conditions (p < 0.005), with maximal values recorded at the beginning of night. Although during sleep deprivation (EPS) the rhythm followed neurophysiological factors, during EAS, this rhythm was accounted for by the variations in the contractile state of muscle.
Assuntos
Ritmo Circadiano/fisiologia , Contração Isométrica/fisiologia , Músculo Esquelético/fisiologia , Privação do Sono/fisiopatologia , Sono/fisiologia , Esportes/fisiologia , Adulto , Humanos , Masculino , TorqueRESUMO
The characterisation of an Arabidopsis thaliana cytochrome P450-encoding cDNA clone, B72, preferentially expressed during the hypersensitive response (HR) provoked by the bacterial pathogen Pseudomonas syringae pathovar maculicola, is reported. The B72 cDNA clone corresponded to the CYP76C2 gene, which belongs to a small multigene family comprising four genes. HR-triggering bacteria harbouring different avirulence genes induced the accumulation of transcripts of this P450 gene. CYP76C2 gene expression was moreover associated with various processes leading to cell death such as leaf senescence, ageing of cell cultures, wounding as well as with treatment with the necrotising heavy metal salt, lead nitrate.
Assuntos
Arabidopsis/enzimologia , Arabidopsis/genética , Sistema Enzimático do Citocromo P-450/genética , Regulação da Expressão Gênica de Plantas , Pseudomonas/fisiologia , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/microbiologia , Clonagem Molecular , Regulação da Expressão Gênica no Desenvolvimento , Regulação Enzimológica da Expressão Gênica , Genes de Plantas , Família Multigênica , Folhas de Planta , Pseudomonas/genética , Pseudomonas/patogenicidade , VirulênciaRESUMO
The Ralstonia solanacearum hrp gene cluster is organized in five transcriptional units. Expression of transcriptional units 2, 3 and 4 is induced in minimal medium and depends on the hrp regulatory gene hrpB, which belongs to unit 1. This regulatory gene also controls the expression of genes, such as popA, located to the left of the hrp cluster. Here, we show that, upon co-culture with Arabidopsis thaliana and tomato cell suspensions, the expression of the hrp transcriptional units 1, 2, 3 and 4 is induced 10- to 20-fold more than in minimal medium. This induction is not triggered by diffusible signals but requires the presence of plant cells. Moreover, we show that this specific plant cell induction of hrp genes is controlled by a gene, called prhA (plant regulator of hrp genes), located next to popA. This gene codes for a putative protein of 770 amino acids, which shows similarities with TonB-dependent outer membrane siderophore receptors. Expression of prhA and hrp genes is not regulated by iron status, and we postulate that iron is not the signal sensed by PrhA. In prhA mutants, the induction of hrpB and other hrp genes is abolished in co-culture with Arabidopsis cells, partially reduced in co-culture with tomato cells and not modified in minimal medium. prhA mutants are hypo-aggressive on Arabidopsis (accessions Col-0 and Col-5) but remain fully pathogenic on tomato plants, suggesting that the co-culture assays mimic the in planta conditions. A model suggesting that PrhA is a receptor for plant specific signals at the top of a novel hrp regulatory pathway is discussed.
Assuntos
Proteínas de Arabidopsis , Proteínas da Membrana Bacteriana Externa , Proteínas de Bactérias/genética , Proteínas de Ligação a DNA , Regulação Bacteriana da Expressão Gênica , Genes Bacterianos , Bacilos e Cocos Aeróbios Gram-Negativos/genética , Proteínas de Homeodomínio/metabolismo , Família Multigênica , Proteínas Repressoras/genética , Fatores de Transcrição , Sequência de Aminoácidos , Arabidopsis , Proteínas de Bactérias/metabolismo , Sequência de Bases , Células Cultivadas , Técnicas de Cocultura , Meios de Cultura , DNA Bacteriano , Bacilos e Cocos Aeróbios Gram-Negativos/metabolismo , Proteínas de Homeodomínio/genética , Ferro/farmacologia , Solanum lycopersicum , Dados de Sequência Molecular , Receptores de Superfície Celular/química , Proteínas Repressoras/metabolismo , Homologia de Sequência de Aminoácidos , Transcrição GênicaRESUMO
The changes in gene expression associated with the reinitiation of cell division and subsequent progression through the cell cycle in Arabidopsis thaliana cell-suspension cultures were investigated. Partial synchronization of cells was achieved by a technique combining phosphate starvation and a transient treatment with the DNA replication inhibitor aphidicolin. Six cDNAs corresponding to genes highly induced in proliferating cells and showing cell-cycle-regulated expression were obtained by the mRNA differential display technique. Full-length cDNA clones (cH2BAt and cH2AvAt) corresponding to two of the display products were subsequently isolated. The cH2BAt clone codes for a novel histone H2B protein, whereas the cH2AvAt cDNA corresponds to a gene encoding a new member of the highly conserved histone H2A.F/Z subfamily of chromosomal proteins. Further studies indicated that H2AvAt mRNA expression is tightly correlated with cell proliferation in cell-suspension cultures, and that closely related analogs of the encoded protein exist in Arabidopsis. The implications of the conservation of histone H2A.F/Z variants in plants are discussed.
Assuntos
Arabidopsis/citologia , Arabidopsis/genética , Ciclo Celular/genética , Regulação da Expressão Gênica de Plantas , Histonas/biossíntese , Transcrição Gênica , Sequência de Aminoácidos , Animais , Afidicolina/farmacologia , Arabidopsis/fisiologia , Divisão Celular/genética , Células Cultivadas , Clonagem Molecular , Sequência Conservada , Replicação do DNA/efeitos dos fármacos , DNA Complementar , Drosophila , Histonas/química , Histonas/genética , Humanos , Dados de Sequência Molecular , RNA Mensageiro/biossíntese , Alinhamento de Sequência , Homologia de Sequência de AminoácidosRESUMO
In an Arabidopsis thaliana T87-C3 cell-suspension culture, entry into the growth-arrest phase is rapidly followed by a loss of cell viability. Three cDNA clones, SRG1, SRG2, and SRG3, corresponding to genes with transcripts that accumulate during these late phases, were isolated by the mRNA differential display method. Amino acid sequence analysis shows that the putative SRG1 protein is a new member of the Fe(II)/ascorbate oxidase superfamily, and that SRG2 codes for a protein with significant homology to beta-glucosidases. Significantly, all three SRG genes are expressed in senescing organs of Arbidopsis plants. Two previously characterized genes, SAG2 and SAG4, induced during natural senescence in Arabidopsis, were also found to be expressed in cell-suspension cultures and have expression kinetics similar to those observed for the SRG1 gene. Taken together these finding suggest that certain molecular events are common to both plant senescence and growth arrest in arabidopsis cell suspensions. Both internucleosomal cleavage of nDNA and an apparent compaction of chromatin, two characteristic features of programmed cell death in animal cells, have been observed in Arabidopsis cell cultures at a stage corresponding to loss of cell viability.
Assuntos
Envelhecimento/genética , Proteínas de Arabidopsis , Arabidopsis/genética , Proteínas de Ciclo Celular , Ciclo Celular/genética , Genes de Plantas , Proteínas de Plantas/genética , Sequência de Aminoácidos , Arabidopsis/citologia , Arabidopsis/crescimento & desenvolvimento , Ascorbato Oxidase/genética , Biomarcadores , Sobrevivência Celular , Células Cultivadas , Celulases , Cromatina/patologia , Clonagem Molecular , Fragmentação do DNA , DNA Complementar/genética , Dados de Sequência Molecular , Família Multigênica , RNA Mensageiro/genética , RNA de Plantas/genética , Análise de Sequência de DNA , Homologia de Sequência de Aminoácidos , beta-Glucosidase/genéticaRESUMO
The recently described mRNA differential display method provides an attractive tool for the isolation of genes showing regulated expression in a variety of systems. A key step in this technique consists of the isolation of PCR-synthesized radioactive cDNAs corresponding to differentially expressed mRNAs. Here, we show that the purified cDNAs remain contaminated with unrelated cDNA sequences that may lead to the artifactual isolation of false positives in the subsequent steps of the method. A powerful assay for the detection and elimination of this contaminating material, allowing the specific isolation of clones corresponding to the regulated genes identified by the differential display, is provided.