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991.
992.
《Current biology : CB》2023,33(2):309-320.e5
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993.
A positive hydraulic signal in the form of a xylem pressure step was applied to the roots of intact seedlings of Cucumis sativus L. and Pisum sativum L. Surface electrodes at three positions along the epicotyl/hypocotyl recorded a propagating depolarization which appeared first in the basal, then the central and sometimes the apical electrode positions and fitted the characteristics of a slow wave potential (SWP). This depolarization differed between pea and cucumber. It was transient in cells of pea epicotyls but sustained in cucumber hypocotyls. It was not associated with a change in cell input resistance in pea epicotyls but preceded an increase in the input resistance of cucumber hypocotyl cells. With the increased xylem pressure the growth rate (GR) of cucumber hypocotyls and pea epicotyls underwent a transient increase, peaking after 5 min. If the depolarization reached the growing upper region, it preceded a sustained decrease in the GR of cucumber hypocotyls but only a transient decrease in the GR of pea epicotyls. A temperature jump in the root medium (heat treatment) induced a steep pressure spike in the xylem of the cucumber hypocotyl which showed similar electric and growth effects as the previously applied, non-injurious pressure steps. We suggest that the observed differences in the electric and growth responses between the species were caused by the closure of ion channels in depolarized cells of cucumber but not pea seedlings. 相似文献
994.
A. MEATS 《Physiological Entomology》1987,12(2):165-170
ABSTRACT. Survival time at subzero temperatures is related to both long-term thermal history and the rate at which the insects are cooled. Insects cooled at one degree per hour survive for up to 3 times as long at a given test temperature than do insects cooled at 1C/min. Survival times are significantly shorter than times taken to freeze. Survival time at an extreme high temperature is related to long-term thermal history but the rate of heating makes no difference. 相似文献
995.
Jrmy Monsimet Herv Colinet Olivier Devineau Denis Lafage Julien Ptillon 《Ecology and evolution》2021,11(7):3347
Most species encounter large variations in abiotic conditions along their distribution range. The physiological responses of most terrestrial ectotherms (such as insects and spiders) to clinal gradients of climate, and in particular gradients of temperature, can be the product of both phenotypic plasticity and local adaptation. This study aimed to determine how the biogeographic position of populations and the body size of individuals set the limits of cold (freezing) resistance of Dolomedes fimbriatus. We compared D. fimbriatus to its sister species Dolomedes plantarius under harsher climatic conditions in their distribution range. Using an ad hoc design, we sampled individuals from four populations of Dolomedes fimbriatus originating from contrasting climatic areas (temperate and continental climate) and one population of the sister species D. plantarius from continental climate, and compared their supercooling ability as an indicator of cold resistance. Results for D. fimbriatus indicated that spiders from northern (continental) populations had higher cold resistance than spiders from southern (temperate) populations. Larger spiders had a lower supercooling ability in northern populations. The red‐listed and rarest D. plantarius was slightly less cold tolerant than the more common D. fimbriatus, and this might be of importance in a context of climate change that could imply colder overwintering habitats in the north due to reduced snow cover protection. The lowest cold resistance might put D. plantarius at risk of extinction in the future, and this should be considered in conservation plan. 相似文献
996.
997.
Although individual neurons can be intrinsically oscillatory and can be network pacemakers, motor patterns are often generated in a more distributed manner. Synaptic connections with other neurons are important because they either modify the rhythm of the pacemaker cell or are essential for pattern generation in the first place. Computational studies of half-center oscillators have made much progress in describing how neurons make transitions between active and inactive phases in these simple networks. In addition to characterizing phase transitions, recent studies have described the synaptic mechanisms that are important for the initiation and maintenance of activity in half-center oscillators. 相似文献
998.
Didier Casane Patrick Laurenti 《BioEssays : news and reviews in molecular, cellular and developmental biology》2013,35(4):332-338
A series of recent studies on extant coelacanths has emphasised the slow rate of molecular and morphological evolution in these species. These studies were based on the assumption that a coelacanth is a ‘living fossil’ that has shown little morphological change since the Devonian, and they proposed a causal link between low molecular evolutionary rate and morphological stasis. Here, we have examined the available molecular and morphological data and show that: (i) low intra‐specific molecular diversity does not imply low mutation rate, (ii) studies not showing low substitution rates in coelacanth are often neglected, (iii) the morphological stability of coelacanths is not supported by paleontological evidence. We recall that intra‐species levels of molecular diversity, inter‐species genome divergence rates and morphological divergence rates are under different constraints and they are not necessarily correlated. Finally, we emphasise that concepts such as ‘living fossil’, ‘basal lineage’, or ‘primitive extant species’ do not make sense from a tree‐thinking perspective. Editor's suggested further reading in BioEssays Tree thinking for all biology: the problem with reading phylogenies as ladders of progress Abstract 相似文献
999.
《Cryobiology》2020
Protein sources used as supplements of IVF culture media are known to have several implications for the function and stability of embryo culture environment. In fact, they i) transport biologically active molecules ii) chelate heavy metals, iii) regulate media pH, iii) scavenge reactive oxygen species (ROS) and iv) attenuate osmotic stress to which cells are exposed in sub-optimal culture conditions. Instead, their specific relevance to the formulation of cryopreservation solutions used for gamete and embryo cryopreservation remains uncertain. In the present work, we tested the hypothesis that different protein supplements present in cryopreservation solutions, serum or plasma protein solution (PPS), or different concentrations of the same supplement (serum), are associated with different types and/or magnitude of cryopreservation-derived cell damage. To this end, using cryopreservation solutions containing serum or PPS, donated supernumerary human mature oocytes were frozen-thawed by slow freezing and compared with fresh controls. Ultrastructural markers of oocyte quality were adopted as objective measure to assess possible damage from cryopreservation. The study results indicate that the adoption of serum minimises cell damage induced by cryopreservation. Indeed, typical hallmarks of cryodamage in human oocytes, i.e. loss of cortical granules, zona pellucida hardening and above all vacuolization, were largely reduced in oocytes cryopreserved with solutions containing serum, especially if used a higher concentration. This suggest that oocyte cryopreservation still has significant margins of improvement that may derive also from composition of cryopreservation media. 相似文献
1000.
Studying the currents in perfused cells or fragments of their membranes with voltage-gated calcium channels and Ca2+-dependent ion channels, it is often expedient to use a buffer that binds Ca2+ slowly. For this purpose, we propose EDTA in excess Mg2+. Calculation of its kinetic characteristics shows that the characteristic time of Ca2+ binding can to be made to reach tens of milliseconds; in the cytoplasm this time does not exceed 1 ms even with a large calcium signal. 相似文献