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61.
We studied the actin cytoskeleton state in Asterias amurensis oocytes within 30 min after the 1-methyladenine-induced maturation until the germinal vesicle breakdown. The total amount of actin remained unchanged during oocyte maturation. In immature oocytes, the major part of actin is not a part of filaments, but in the presence of 1-methyladenine massive actin polymerization began already within 20 min. Electron immunocytochemistry methods demonstrated joint localization of actin and alpha-protein in the cytoplasm. They were redistributed from the cortex to the cytoplasm in the presence of 1-methyladenine. A possible involvement of actin cytoskeleton in transmembrane transduction of the hormonal signal at the postreceptor stages is discussed. 相似文献
62.
CHRISTOPHER R. TRACY KEITH A. CHRISTIAN NICOLE BURNIP BEAU J. AUSTIN ALYSSA CORNALL SEBASTIAN IGLESIAS STEPHEN J. REYNOLDS THOMAS TIXIER CAMILLE LE NOËNE 《Austral ecology》2013,38(4):476-483
Amphibians are typically intolerant of high temperatures and dehydrating conditions, and small species are particularly susceptible to desiccation. The rockhole frog, Litoria meiriana (Hylidae), is diurnal and is often observed on rocks in the sun near streams in tropical Australia. These hot, desiccating conditions are avoided by most frog species. We measured the microclimate in the areas used by frogs and the activity, body temperatures and hydric state of free‐ranging individuals of this small frog. We also used plaster models to further explore the dynamic nature of hydric state by combining estimates of water loss and water uptake with behavioural observations of activity and microhabitat selection. Both direct measures and estimates of dynamic hydric state indicated that free‐ranging frogs generally maintained a hydric state above 95% of full hydration, but occasionally, particularly during the afternoon, frogs allowed their hydric state to fall as low as 85%. Body temperatures of frogs remained below the critical thermal maximum (CTmax) even when the frogs were in the sun, because this species has no cutaneous resistance to evaporative water loss and so they cool by evaporation. However, during the hotter part of the day, on dry sunny substrates, the hydric state of the frogs could fall to near lethal hydration states (approximately 70% of full hydration) within a short period (approximately 20 min). Thus, the threat of desiccation appears to be more limiting than the threat of overheating. These diurnal frogs rely on frequent bouts of rehydration to support their ability to venture onto hot, dry rocks during the day. 相似文献
63.
W. I. J. DIELEMAN S. LUYSSAERT A. REY P. DE ANGELIS C. V. M. BARTON M. S. J. BROADMEADOW S. B. BROADMEADOW K. S. CHIGWEREWE M. CROOKSHANKS E. DUFRÊNE P. G. JARVIS A. KASURINEN S. KELLOMÄKI V. LE DANTEC M. LIBERLOO M. MAREK B. MEDLYN R. POKORNÝ G. SCARASCIA‐MUGNOZZA V. M. TEMPERTON D. TINGEY O. URBAN R. CEULEMANS I. A. JANSSENS 《Plant, cell & environment》2010,33(12):2001-2011
Under elevated atmospheric CO2 concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO2 effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta‐analysis to test the hypotheses that: (1) elevated atmospheric CO2 stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO2 induces a C allocation shift towards below‐ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO2. Soil N concentration strongly interacted with CO2 fumigation: the effect of elevated CO2 on fine root biomass and –production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO2 are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses. 相似文献
64.
Voskamp KE; Noorman N; Mastebroek HA; Van Schoot NE; Den Otter CJ 《Chemical senses》1998,23(5):521-530
Spike trains from individual antennal olfactory cells of tsetse flies
(Glossina spp.) obtained during steady-state conditions (spontaneous as
well as during stimulation with 1-octen-3-ol) and dynamic stimulation with
repetitive pulses of 1-octen-3-ol were investigated by studying the spike
frequency and the temporal structure of the trains. In general, stimulation
changes the intensity of the spike activity but leaves the underlying
stochastic structure unaffected. This structure turns out to be a renewal
process. The only independently varying parameter in this process is the
mean interspike interval length, suggesting that olfactory cells of tsetse
flies may transmit information via a frequency coding. In spike records
with high firing rates, however, the stationary records had significant
negative first- order serial correlation coefficients and were non-renewal.
Some cells in this study were capable of precisely encoding the onset of
the odour pulses at frequencies up to at least 3 Hz. Cells with a rapid
return to pre-stimulus activity at the end of stimulation responded more
adequately to pulsed stimuli than cells with a long increased spike
frequency. While short-firing cells process information via a frequency
code, long-firing cells responded with two distinctive phases: a phasic,
non-renewal response and a tonic, renewal response which may function as a
memory of previous stimulations.
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