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41.
Almond plants (Amygdalus communis L.) of the Garrigues variety were grown in the field drip irrigated and rainfed. Leaf water potential (Ψ) and leaf conductance
(g1) were determined throughout one growing season. Pre-dawn measurement for Ψ in the irrigated treatment was consistent through
the growing season, whereas in the rainfed treatment it decreased gradually. Ψ values at midday (Ψ minimum) was closely dependent
on atmospheric evaporative demand, and their recovery was quicker in the wet treatment than in the dry. The g1 values were higher in the wet than dry treatments, decreasing in both cases by leaf ageing. Maximum values for g1 were reached when evaporative demand was highest in the day. The relationship between Ψ and g1 revealed a decrease in the hysteresis throughout the growing season, being most marked in the dry treatment. The results
highlight the close dependence of Ψ and g1 on evaporative demand, leaf ageing and irrigtion treatment during the growing season. 相似文献
42.
Almond plants (Amygdalus communis L. cv. Garrigues) were grown in the field under drip irrigated and non irrigated conditions. Leaf water potential () and leaf conductance (g1) were determined at three different times of the growing season (spring, summer and autumn). The relationships between and g1 in both treatments showed a continuous decrease of g1 as decreased in spring and summer. Data from the autumn presented a threshold value of (approx. –2.7 MPa in dry treatment, and approx. –1.4 MPa in wet treatment) below which leaf conductance remained constant. 相似文献
43.
Giuseppe Cassano Michele Maffia Sebastiano Vilella Carlo Storelli 《The Journal of membrane biology》1988,101(1):225-236
Summary The Na-dependent transport of a number of organic molecules (d-glucose,l-proline,l-alanine,l-phenylalanine) in brush-border membrane vesicles isolated from the intestine of the eel (Anguilla anguilla) was monitored by recording the fluorescence quenching of the voltage-sensitive cyanine dye 3,3-diethylthiacarbocyanine iodide (DiS-C2(5)). The experimental approach consisted of: a) generating an inside-negative membrane potential mimicking in vivo conditions: b) measuring the rate of membrane potential decay (i.e., the rate of fluorescence quenching decay) due to Na-neutral substrate cotransport. Rates of membrane potential decay showed saturation on substrate concentration andK
app values (the substrate concentration giving 50% of the maximal rate) were estimated for Na-dependent transport ofd-glucose (0,099mm),l-alanine (0.516mm),l-proline (0.118mm) andl-phenylalanine (2.04mm). The influence of an inside-negative membrane potential on the affinity of the transporter for glucose and for sodium is discussed. 相似文献
44.
Mark Tester 《The Journal of membrane biology》1988,105(1):77-85
Summary The outer membranes of plant cells contain channels which are highly selective for K+. In the giant-celled green algaChara corallina, K+ currents in the plasmalemma were measured during the action potential and when the cell was depolarized to the K+ equilibrium potential in high external K+ concentrations. Currents in both conditions were reduced by externally added tetraethylammonium (TEA+), Ba2+, Na+ and Cs+. In contrast to inhibition by TEA+, the latter three ions inhibited inward K+ current in a voltage-dependent manner, and reduced inward current more than outward. Ba2+ and Na+ also appeared to inhibit outward current in a strongly voltage-dependent manner. The blockade by Cs+ is studied in more detail in the following paper. TEA+ inhibited both inward and outward currents in a largely voltage-independent manner, with an apparentK
D
of about 0.7 to 1.1mm, increasing with increasing external K+. All inhibitors reduced current towards a similar linear leak, suggesting an insensitivity of the background leak inChara to these various K+ channel inhibitors. The selectivity of the channel to various monovalent cations varied depending on the method of measurement, suggesting that ion movement through the K+-selective channel may not be independent. 相似文献
45.
Summary A systematic study was made of the action of 4-acetamido-4-isothiocyanostilbene-2,2-disulfonic acid (SITS) and 4,4-diisothiocyanostilbene-2,2-disulfonic acid (DIDS) on active Ca2+ transport of human erythrocytes. Pumping activity was estimated in inside-out vesicles (IOV's) by means of Ca2+-selective electrodes or use of tracer45Ca2+. The stilbenes exhibited an approximately equal inhibitory potency and their action could be overcome by carbonyl cyanidep-trifluoromethoxyphenylhydrazone (FCCP) at low but not at high stilbene concentrations. In the absence of DIDS. Ca2+ transport was not affected upon addition of valinomycin, but it was appreciably reduced when vesicles were preincubated with low DIDS concentrations. Such an effect was strictly dependent on the external K+ concentration and it was abolished when valinomycin was added together with FCCP. Similar results were obtained using IOV's prepared from intact cells which had been previously exposed to the stilbene. The findings clearly demonstrate the presence in human red cells of a partially electrogenic Ca2+ pump, exchanging one Ca2+ ion for one proton. 相似文献
46.
Sacco C. de Vries Hilbert Booij Peter Meyerink Gert Huisman H. Dayton Wilde Terry L. Thomas Ab van Kammen 《Planta》1988,176(2):196-204
Embryogenic suspension cultures of domesticated carrot (Daucus carota L.) are characterized by the presence of proembryogenic masses (PEMs) from which somatic embryos develop under conditions of low cell density in the absence of phytohormones. A culture system, referred to as starting cultures, was developed that allowed analysis of the emergence of PEMs in newly initiated hypocotyl-derived suspension cultures. Embryogenic potential, reflected by the number of FEMs present, slowly increased in starting cultures over a period of six weeks. Addition of excreted, high-molecular-weight, heat-labile cell factors from an established embryogenic culture considerably accelerated the acquisition of embryogenic potential in starting cultures. Analysis of [35S]methionine-labeled proteins excreted into the medium revealed distinct changes concomitant with the acquisition of embryogenic potential in these cultures. Analysis of the pattern of gene expression by in-vitro translation of total cellular mRNA from starting cultures with different embryogenic potential and subsequent separation of the [35S]methionine-labeled products by two-dimensional polyacrylamide gel electrophoresis demonstrated a small number of abundant in-vitro-translation products to be present in somatic embryos and in embryogenic cells but absent in nonembryogenic cells. Several other in-vitro-translation products were present in explants, non-embryogenic and embryogenic cells but were absent in somatic embryos. Hybridization of an embryoregulated complementary-DNA sequence, Dc3, to RNA extracted from starting cultures showed that the corresponding gene is expressed in somatic embryos and PEMs but not in non-embryogenic cells.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- cDNA
complementary DNA
- PAGE
polyacrylamide gel electrophoresis
- PEM
proembryogenic mass 相似文献
47.
Roman G. Efremov Dmitry I. Gulyaev Gerard Vergoten Nikolai N. Modyanov 《Journal of Protein Chemistry》1992,11(6):665-675
A new computer-aided molecular modeling approach based on the concept of three-dimensional (3D) molecular hydrophobicity potential has been developed to calculate the spatial organization of intramembrane domains in proteins. The method has been tested by calculating the arrangement of membrane-spanning segments in the photoreaction center ofRhodopseudomonas viridis and comparing the results obtained with those derived from the X-ray data. We have applied this computational procedure to the analysis of interhelical packing in membrane moiety of Na+, K+-ATPase. The work consists of three parts. In Part I, 3D distributions of electrostatic and molecular hydrophobicity potentials on the surfaces of transmembrane helical peptides were computed and visualized. The hydrophobic and electrostatic properties of helices are discussed from the point of view of their possible arrangement within the protein molecule. Interlocation of helical segments connected with short extramembrane loops found by means of optimization of their hydrophobic/hydrophilic contacts is considered in Part II. The most probable 3D model of packing of helical peptides in the membrane domain of Na+, K+-ATPase is discussed in the final part of the work. 相似文献
48.
The protonmotive force in several sulfate-reducing bacteria has been determined by means of radiolabelled membrane-permeant probes (tetraphenyl-phosphonium cation, TPP+, for , and benzoate for pH). In six of ten freshwater strains tested only the pH gradient could be determine, while the membrane potential was not accessible due to nonspecific binding of TPP+. The protonmotive force of the other four strains was between –110 and –155 mV, composed of a membrane potential of –80 to –140 mV and a pH gradient between 0.25 and 0.8 (inside alkaline) at pHout=7. In Desulfobulbus propionicus the pH gradient decreased with rising external pH values. This decrease, however, was compensated by an increasing membrane potential. Sulfate, which can be highly accumulated by the cells, did not affect the protonmotive force, if added in concentrations of up to 4 mM. The highest sulfate accumulation observed (2500-fold), which occurred at external sulfate concentrations below 5 M, could be explained by a symport of three protons per sulfate, if equilibrium with the protonmotive force was assumed. At higher sulfate concentrations the accumulation decreased and suggested an electroneutral symport of two protons per sulfate. At sulfate concentrations above 500 M, the cells stopped sulfate uptake before reaching an equilibrium with the protonmotive force.Abbreviations CCCP
carbonyl cyanide m-chlorophenylhydrazone
- MOPS
morpholinopropanesulfonic acid
- TPP+
tetraphenylphosphonium cation
- EDTA
ethylenediaminetetraacetic acid
- pH
transmembrane pH gradient (pHin-pHout)
-
transmembrane electrical potential difference 相似文献
49.
Alexander I. Roitbak Elijah V. Ocherashvili Peter R. Laming Tamara A. Roitbak 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1992,170(3):327-333
Summary In 17 frogs (Rana esculenta var ridibunda) immobilised with succinyl choline the optic tectal surface was stimulated by trains of electrical pulses or by a flash to the contralateral eye. Sustained potential shifts (SPSs) and changes in extracellular potassium concentration ( [K+]0) were simultaneously recorded.In response to electrical stimulation SPSs of maximal amplitudes (1.19±0.1 mV) were recorded between 50 and 200 m in depth and maximal [K+]0 (0.69 ±0.08 mM) between 100 and 350 m. The changes of SPS and [K+]0 showed a close similarity in experiments with changes in voltage, pulse duration and frequency of stimuli within a train. The induced SPS had a duration of 28±1.54 s, the [K+]0 of 32±1.23 s.The flash stimulus induced an SPS and [K+]0 of maximal amplitudes between 50 and 200 m in depth with values of 0.57±0.1 mV and 0.29±0.03 mM respectively. An additional wave with a latency of ca 1 s and a duration of ca 3 s arose on the background of the SPS to a flash stimulus, associated with an additional increase in [K+]0.It is considered that the accumulation of K+ in extra-cellular space, with neuronal activity, results in depolarization of radial processes of ependymal glia. This is reflected in the neuropil of the upper layers of the optic tectum as an SPS.We would like to dedicate this article to the memory of Alexander Roitbak who died as a result of a tragic accident while this paper was in press. He will be remembered fondly especially for his contributions to understanding of the functions of Neuroglia. E.V.O., P.R.L., T.A.R. 相似文献
50.
In our previous study vesamicol, an inhibitor of the acetylcholine transporter of the cholinergic vesicles, inhibited veratridine-evoked external Ca2+-dependent acetylcholine release from striatal slices but did not influence acetylcholine release observed in Ca2+-free medium (4). Here we examined if the effect of veratridine on membrane potential, Ca2+ uptake, and intracellular Ca2+ concentration of synaptosomes was altered by vesamicol in parallel with the inhibition of acetylcholine release. The depolarizing effect of 10 M veratridine (from 67±2.3 mV resting membrane potential to 50.7±2.5 mV) was not significantly influenced by vesamicol (1–20 M). Vesamicol (1–20 M) had no effect on either the overall curve of the veratridine-evoked45Ca2+ uptake or the amount of Ca2+ taken up by synaptosomes. Veratridine caused a rise in intrasynaptosomal Ca2+ concentration as measured by Fura2 fluorescence, and the same increase both in characteristics and in magnitude was observed in the presence of vesamicol (20 M). The K+-evoked (40 mM) increase of Ca2+ uptake and of intracellular calcium concentration were also unaltered by vesamicol. In high concentration (50 M) vesamicol inhibited both the fall in membrane potential and the elevated Ca2+ uptake by veratridine, indicating a possible nonspecific effect on potential-dependent Na+ channels at this concentration. Vesamicol, in lower concentration (20 M) when neither of the above parameters was changed, completely prevented veratridine-evoked increase of [14C]acetylcholine release. This was observed only when vesamicol was present in the media throughout the experiment after loading the preparation with [14C]choline. The results suggest that vesamicol does not interfere with veratridine-induced changes in isolated nerve terminals other than with the release of acetylcholine, thus further supporting the involvement of a vesamicol-sensitive vesicular transmitter pool in Ca2+-dependent veratridine-elicited acetylcholine release. 相似文献