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1.
It is suggested that photophobic responses caused by a sudden step-down in light intensity require the presence of cations in the blue-green alga, Phormidium uncinatum.Drastic removal of cations abolishes the phobic response, which recovers after addition of Ca2+ ions. Calcium can be substituted for partially by other cations with an effectivity following the sequence Ca>Mg>Na>Ba>Co=0. During the photophobic response there is a 25% increase in 45Ca binding by the cells related to a step-down in light intensity. Three seconds after a light-dark transition there is a sharp increase in the binding of labelled calcium, followed by a subsequent release.Flushing the filaments with high cation concentrations, esp. calcium causes a reversal of movement in the absence of a light stimulus similar to a photophobic reversal. This stimulus could trigger the same sequence of events in the transduction chain bypassing the primary photoresponse.Abbreviations EDTA Ethylene diaminetetraacetic acid - EGTA ethylene glycol-bis (2-aminoethylether) N,N tetraacetic acid  相似文献   

2.
Negative phototactic orientation, step-up photophobic responses and light-induced action potentials have been studied in the ciliate Stentor coeruleus. A resolved action spectrum, based on fluence rate-response curves, is consistent with stentorin as the photoreceptor. Calcium flux blockers prolong the response time for ciliary stop and reversal and inhibit step-up photophobic responses. Drugs believed to affect the membrane-bound calcium pump likewise inhibit phobic responses. On the other hand, α-phosphatidic acid promotes Ca2+-influx and enhances the photophobic sensitivity of the organism, thus providing an unambiguous evidence for the role of Ca2+ influx. A change in the response time decreases the degree of phototactic orientation, indicating that negative phototaxis in this organism is brought about by subsequent phobic responses of individual rows of cilia as the associated photoreceptor granules experience an increase in light intensity when the organism rotates during forward locomotion in lateral light.  相似文献   

3.
SYNOPSIS. The effect of temperature on photoaccumulation and photophobic response of Volvox aureus were studied. The algae exhibited positive photoaccumulation at room temperature and negative at low temperature. When stimulated with light of intermediate intensiy (~ 5 × 103 lux), the phobic response of the algae consisted of a decrease in the frequency or the cessation of flagellar movement in the anterior cells. At room temperature, an increase in light intensity elicited the phobic response, whereas at low temperature a decrease in light intensity was the effective stimulus. The phobic response lasted only a few seconds. The positive and negative photoaccumulations of the algae could be explained by the brief cessation of flagellar movement in the anterior cells, elicited by an increase of stimulus light at room temperature or a decrease of stimulus at low temperature.  相似文献   

4.
Calcium ion (Ca2+) is one of the very important ubiquitous intracellular second messenger molecules involved in many signal transduction pathways in plants. The cytosolic free Ca2+ concentration ([Ca2+]cyt) have been found to increased in response to many physiological stimuli such as light, touch, pathogenic elicitor, plant hormones and abiotic stresses including high salinity, cold and drought. This Ca2+ spikes normally result from two opposing reactions, Ca2+ influx through channels or Ca2+ efflux through pumps. The removal of Ca2+ from the cytosol against its electrochemical gradient to either the apoplast or to intracellular organelles requires energized ‘active’ transport. Ca2+-ATPases and H+/Ca2+ antiporters are the key proteins catalyzing this movement. The increased level of Ca2+ is recognised by some Ca2+-sensors or calcium-binding proteins, which can activate many calcium dependent protein kinases. These kinases regulate the function of many genes including stress responsive genes, resulted in the phenotypic response of stress tolerance. Calcium signaling is also involved in the regulation of cell cycle progression in response to abiotic stress. The regulation of gene expression by cellular calcium is also crucial for plant defense against various stresses. However, the number of genes known to respond to specific transient calcium signals is limited. This review article describes several aspects of calcium signaling such as Ca2+ requiremant and its role in plants, Ca2+ transporters, Ca2+-ATPases, H+/ Ca2+-antiporter, Ca2+-signature, Ca2+-memory and various Ca2+-binding proteins (with and without EF hand).Key Words: Calcium binding proteins, Ca2+ channel, Ca2+-dependent protein kinases, Ca2+/H+ antiport, calcium memory, calcium sensors, calcium signatures, Ca2+-transporters, EF hand motifs, plant signal transduction  相似文献   

5.
The motility and step-down photophobic responses of Euglena are influenced by inorganic and organic anions. Persistent motility (with Ca2+, Mg2+ and K+ present) is supported with chloride or sulfate but not with acetate, nitrate or propionate as the only added anions. Cells in media containing acetate displayed a cell aggregation (clumping) behavior that was both red light sensitive and, under some conditions, was accompanied by suppression of the step-down photophobic response. Addition of sodium salts (Cl-, SO 4 2- , acetate or propionate) to cells in Cl- or SO 4 2- based media had differential effects on the duration of the step-down photophobic responses induced by blue light removal: anions alter the response. In addition, cells in all Cl- containing media showed constant photophobic response duration following repeated stimulation. Cells in some SO4 2- containing media, however, showed response summation to repeated stimulation. This latter effect was reversible and was overcome by the addition of chloride anions.  相似文献   

6.
Pittman JK 《Cell calcium》2011,50(2):139-146
Calcium transporters that mediate the removal of Ca2+ from the cytosol and into internal stores provide a critical role in regulating Ca2+ signals following stimulus induction and in preventing calcium toxicity. The vacuole is a major calcium store in many organisms, particularly plants and fungi. Two main pathways facilitate the accumulation of Ca2+ into vacuoles, Ca2+-ATPases and Ca2+/H+ exchangers. Here I review the biochemical and regulatory features of these transporters that have been characterised in yeast and plants. These Ca2+ transport mechanisms are compared with those being identified from other vacuolated organisms including algae and protozoa. Studies suggest that Ca2+ uptake into vacuoles and other related acidic Ca2+ stores occurs by conserved mechanisms which developed early in evolution.  相似文献   

7.
Kenneth R. Robinson 《Planta》1996,198(3):378-384
The initially apolar zygotes of the brown algae,Fucus andPelvetia, form their main axes during the hours following fertilization and each cell expresses its axis by germinating at one location. The germinating region is destined to become the rhizoid and the rest of the zygote gives rise to the thallus. In response to unilateral blue light, the zygotes organize their developmental axes so that the rhizoids emerge on the shaded side, away from the light source. In the research reported here, the signaltransduction elements involved in the photopolarization ofPelvetia fastigiata De Toni zygotes have been investigated. It was found that exposure of zygotes to 90or 150-min pulses of unilateral light in the absence of extracellular Ca2+ completely eliminated photopolarization; that is, the cells formed their rhizoid-thallus axes randomly with respect to the light direction, while controls similarly exposed to light in normal (10 mM) Ca2+ were well polarized. When the cells were incubated in Ca2+-free sea water for an hour before being given the light pulse (while still in Ca2+-free sea water), they exhibited an unusual negative polarization: they formed their rhizoids on the hemisphere nearer the light source. Organic and inorganic calcium-channel blockers reduced or abolished photopolarization when present during light pulses. Reducing external Ca2+ to one-tenth of normal has the paradoxical effect of increasing calcium influx intoPelvetia zygotes. When zygotes were given light pulses in reduced extracellular calcium, the degree of photopolarization was increased substantially. These data are consistent with the idea that the formation of an intracellular gradient of [Ca2+] is an essential part of the polarization process. The fungus-derived calmodulin antagonist, ophiobolin A, blocked or greatly delayed germination when present continuously at a concentration of 100–300 nM. However, when present at 300 nM during a brief light pulse, it markedly increased the sensitivity of the cells to light. These results suggest that calmodulin may be the mediator of intracellular [Ca2+] gradients in the photopolarization process.  相似文献   

8.
Markus Braun  Peter Richter 《Planta》1999,209(4):414-423
The localization of cytoplasmic free calcium and a dihydropyridine (DHP) receptor, a putative calcium channel, was recorded during the opposite graviresponses of tip-growing Chara rhizoids and Chara protonemata by using the calcium indicator Calcium Crimson and a fluorescently labeled dihydropyridine (FL-DHP). In upward (negatively gravitropically) growing protonemata and downward (positively gravitropically) growing rhizoids, a steep Ca2+ gradient and DHP receptors were found to be symmetrically localized in the tip. However, the localization of the Ca2+ gradient and DHP receptors differed considerably during the gravitropic responses upon horizontal positioning of the two cell types. During the graviresponse of rhizoids, a continuous bowing downward by differential flank growth, the Ca2+ gradient and DHP receptors remained symmetrically localized in the tip at the centre of growth. However, after tilting protonemata into a horizontal position, there was a drastic displacement of the Ca2+ gradient and FL-DHP to the upper flank of the apical dome. This displacement occurred after the apical intrusion and sedimentation of the statoliths but clearly before the change in the growth direction became evident. In protonemata, the reorientation of the growth direction started with the appearence of a bulge on that site of the upper flank which was predicted by the asymmetrically displaced Ca2+ gradient. With the upward shift of the cell tip, which is suggested to result from a statolith-induced displacement of the growth centre, the Ca2+ gradient and DHP receptors became symmetrically relocalized in the apical dome. No major asymmetrical rearrangement was observed during the following phase of gravitropic curvature which is characterized by slower rates of bending. Labeling with FL-DHP was completely inhibited by a non-fluorescently labeled dihydropyridine. From these results it is suggested that FL-DHP labels calcium channels in rhizoids and protonemata. In rhizoids, positive gravitropic curvature is caused by differential growth limited to the opposite subapical flanks of the apical dome, a process which does not involve displacement of the growth centre, the calcium gradient or calcium channels. In protonemata, however, it is proposed that a statolith-induced asymmetrical relocalization of calcium channels and the Ca2+ gradient precedes, and might mediate, the rearrangement of the centre of growth, most likely by the displacement of the Spitzenk?rper, to the upper flank, which results in the negative gravitropic reorientation of the growth direction. Received: 13 February 1999 / Accepted: 25 June 1999  相似文献   

9.
10.
Theoretical analysis of peculiarities of reception of weak extremely low-frequency periodic signals by calcium-dependent intracellular regulatory systems was performed on the reduced “minimal” model for calcium oscillations suggested by Goldbeter et al. (Proc. Natl. Acad. Sci. USA 87, 1461–1465, 1990). The model considered the following calcium-dependent processes: the rise in intracellular free calcium concentration ([Ca2+]i) due to calcium ionophore A23187 action on a cell, activation of the Ca2+ entry through calcium channels in the plasma membrane by the initial rise in [Ca2+]i, and the Ca2+ release from intracellular stores by the calcium-induced calcium release mechanism. Calcium channels of plasma membrane were chosen as a target for the modulating signal and an additive noise influence in the model. An increase in [Ca2+]i under the influence of the modulating signal was demonstrated to depend not only on the amplitude and frequency of this signal, but also on the phase of the signal with respect to a momentary chemical stimulation of the cell. Such an effect was found only at high strengths of chemical stimulation and with a particular sequence of delivery of the chemical and electromagnetic stimuli. An increase in noise intensity led to magnification of the mean level of [Ca2+]i in a narrow frequency range by the mechanism of stochastic resonance. Under the influence of a modulating periodic signal, the gradual increase in strength of chemical stimulation induced a system transition from regular to chaotic behavior, and then to induced periodic oscillations. A boundary of the transition from chaotic to periodic oscillations corresponded to a “threshold” of sensitivity of calcium-dependent intracellular signaling systems on [Ca2+]i to the influence of the modulating signal. Results of the theoretical analysis led us to conclude that the narrow-band response of a system to an external electromagnetic signal is determined purely by nonlinear properties of the system.  相似文献   

11.
Flagellar activity in the biflagellate chlorophyte Chlamydomonas reinhardtii is selectively inhibited by Ni2+ or by treatment with Ca2+-chelating agents. Inhibitions of swimming speed, geotaxis, phototaxis, and pattern swimming result from qualitative and quantitative losses in the activity of individual flagella and in the coordination of activity beween the 2 flagella of each cell. Addition of Ca2+ (a) prevents inhibition and (b) restores normal flagellar activity in inhibited cells. Mg2+ is partially effective in reversal of inhibition. Other ions do not cause similar inhibition or reversal of nickel inhibition. The characteristics of inhibition and reversal suggest that the prmary target for nickel is a component of the flagellar apparatus, and that this component uses Ca2+ to perform its normal function in the regulation of flagellar activity. A 2nd target for nickel is a Carequiring process specific to phototaxis (and not involved in the photophobic response).  相似文献   

12.
Robert V  Triffaux E  Savignac M  Pelletier L 《Biochimie》2011,93(12):2087-2094
Calcium signalling is essential for most of the biological T-cell activities, including in Th2 lymphocytes, a T-cell subset that produce interleukin 4, 5 and 13 and which is involved in allergic diseases. T-cell receptor engagement induces the production of inositol trisphosphate that binds to its receptor, releasing intracellular Ca2+ stores. STIM in the endo (sarco) plasmic reticulum (ER/SR) is a Ca2+ sensor that perceives the depletion of intracellular Ca2+ stores, localizes near the cell membrane and allows the activation of ORAI, the main calcium channels at the cell membrane. However, other calcium channels at the membrane of intracellular compartments and at the cell membrane can also contribute to the TCR-driven intracellular Ca2+ rise. Among them, voltage-dependent calcium (Cav1) channels have been reported in several types of T-lymphocytes, although how they are gated in these non-excitable cells remains unsolved. We have shown that Cav1 channel expression was selectively up regulated in Th2 lymphocytes. In this review, we will discuss about the diversity of the Ca2+ channels responsible for Ca2+ homeostasis in the different cell subsets and the interactions between these molecules, which can account for the variety of the calcium responses depending upon the functions of effector T-cells.  相似文献   

13.
A strong stimulus adjusting the circadian clock to the prevailing light-dark cycle is light. However, the circadian clock is reset by light only at specific times of the day. The mechanisms mediating such gating of light input to the CNS are not well understood. There is evidence that Ca2+ ions play an important role in intracellular signaling mechanisms, including signaling cascades stimulated by light. Therefore, Ca2+ is hypothesized to play a role in the light-mediated resetting of the circadian clock. Calbindin-D28k (CB; gene symbol: Calb1) is a Ca2+ binding protein implicated in Ca2+ homeostasis and sensing. The absence of this protein influences Ca2+ buffering capacity of a cell, alters spatio-temporal aspects of intracellular Ca2+ signaling, and hence might alter transmission of light information to the circadian clock in neurons of the suprachiasmatic nuclei (SCN). We tested mice lacking a functional Calb1 gene (Calb1?/?) and found an increased phase-delay response to light applied at circadian time (CT) 14 in these animals. This is accompanied by elevated induction of Per2 gene expression in the SCN. Period length and circadian rhythmicity were comparable between Calb1?/? and wild-type animals. Our findings indicate an involvement of CB in the signaling pathway that modulates the behavioral and molecular response to light. (Author correspondence: )  相似文献   

14.
Sensory cells adjust their sensitivity to incoming signals, such as odor or light, in response to changes in background stimulation, thereby extending the range over which they operate. For instance, rod photoreceptors are extremely sensitive in darkness, so that they are able to detect individual photons, but remain responsive to visual stimuli under conditions of bright ambient light, which would be expected to saturate their response given the high gain of the rod transduction cascade in darkness. These photoreceptors regulate their sensitivity to light rapidly and reversibly in response to changes in ambient illumination, thereby avoiding saturation. Calcium ions (Ca2+) play a major role in mediating the rapid, subsecond adaptation to light, and the Ca2+-binding proteins GCAP1 and GCAP2 (or guanylyl cyclase–activating proteins [GCAPs]) have been identified as important mediators of the photoreceptor response to changes in intracellular Ca2+. However, mouse rods lacking both GCAP1 and GCAP2 (GCAP−/−) still show substantial light adaptation. Here, we determined the Ca2+ dependency of this residual light adaptation and, by combining pharmacological, genetic, and electrophysiological tools, showed that an unknown Ca2+-dependent mechanism contributes to light adaptation in GCAP−/− mouse rods. We found that mimicking the light-induced decrease in intracellular [Ca2+] accelerated recovery of the response to visual stimuli and caused a fourfold decrease of sensitivity in GCAP−/− rods. About half of this Ca2+-dependent regulation of sensitivity could be attributed to the recoverin-mediated pathway, whereas half of it was caused by the unknown mechanism. Furthermore, our data demonstrate that the feedback mechanisms regulating the sensitivity of mammalian rods on the second and subsecond time scales are all Ca2+ dependent and that, unlike salamander rods, Ca2+-independent background-induced acceleration of flash response kinetics is rather weak in mouse rods.  相似文献   

15.
Semaphorin 3A (Sema3A) is a secreted protein involved in axon path-finding during nervous system development. Calcium signaling plays an important role during axonal growth in response to different guidance cues; however it remains unclear whether this is also the case for Sema3A. In this study we used intracellular calcium imaging to figure out whether Sema3A-induced growth cone collapse is a Ca2+ dependent process. Intracellular Ca2+ imaging results using Fura-2 AM showed Ca2+ increase in E15 mice dorsal root ganglia neurons upon Sema3A treatment. Consequently we analyzed Sema3A effect on growth cones after blocking or modifying intracellular and extracellular Ca2+ channels that are expressed in E15 mouse embryos. Our results demonstrate that Sema3A increased growth cone collapse rate is blocked by the non-selective R- and T- type Ca2+ channel blocker NiCl2 and by the selective R-type Ca2+ channel blocker SNX482. These Ca2+ channel blockers consistently decreased the Sema3A-induced intracellular Ca2+ concentration elevation. Overall, our results demonstrate that Sema3A-induced growth cone collapses are intimately related with increase in intracellular calcium concentration mediated by R-type calcium channels.  相似文献   

16.
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 Ca2+ showed that this cell was bounded by a thin layer of medium that was depleted in K+ and Ca2+ and exhibited a lower pH than the bulk solution. Both the K+ and Ca2+ 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+, Ca2+, 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.  相似文献   

17.
Calcium regulation in melanocytes affects numerous biological pathways including protecting the redox balance in the cell and regulating the supply of substrate, l ‐tyrosine, for melanogenesis. The pigment contained in the melanocytes, melanin, has been implicated in maintaining calcium homeostasis in the cell and is known to be involved with calcium ion regulation in the inner ear. Herein, the association constant for Ca2+ binding to Sepia melanin is determined by isothermal titration calorimetry to be 3.3 (±0.2) × 103/M. This value is comparable with other well‐established intracellular calcium‐binding proteins that serve to buffer calcium concentrations, lending further support to the hypothesis that melanosomes serve as intracellular mediators of calcium homeostasis in melanocytes. Using this binding constant and the data from a fluorescent Ca2+ displacement assay, the pKa of the carboxyl group coordinated to Ca2+ is determined to be 3.1 ± 0.1.  相似文献   

18.
Rat submandibular glands were digested with crude collagenase, and the intracellular calcium concentration of the cellular suspension was measured using fura-2. In the absence of extracellular magnesium and calcium ([Ca2+]o), ATP had no effect; the response to ATP peaked at 1–2.5 mM [Ca2+]o and was inhibited at 5 mM. One millimolar (mM) extracellular ATP did not increase the leak of LDH or fura-2; 10 m?M Coomassie brilliant blue G specifically inhibited the effect of ATP on [Ca2+]in. Depleting intracellular calcium pools with thapsigargin did not affect the response to ATP. Using a Ca2+-free/Ca2+ reintroduction protocol, it was shown that ATP and thapsigargin increase the uptake of extracellular calcium. The effect of the two agonists was synergistic. Removal of extracellular sodium inhibited the effect of carbachol on [Ca2+]in and the calcium uptake but potentiated the response to ATP. These results suggest that, after binding to purinergic receptors, extracellular ATP4- increases [Ca2+]in. ATP4- does not mobilize thapsigargin-sensitive intracellular calcium pools (among which is the IP3-sensitive calcium pool) but stimulates the uptake of extracellular calcium by a mechanism inhibited by extracellular sodium, probably by opening a nonselective cation channel. © 1994 Wiley-Liss, Inc.  相似文献   

19.
Calcium signaling system in plants   总被引:4,自引:0,他引:4  
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20.
Nitric oxide (NO) and calcium channel blockers are two agents that can affect gastrointestinal motility. The goal of this work was to study the rabbit intestinal smooth muscle contraction response to (1) sodium nitroprusside (SNP), the NO donor, and its potential mechanism of action, and (2) nifedipine, the l-type Ca2+ channel blocker; to clarify the degree of participation by extra- and intracellular Ca2+ in smooth muscle contraction. We used standard isometric tension and intracellular micro-electrode recordings. To record the activity of the longitudinal smooth muscle of the ileum, segments of 1.5?cm length of the ileum were suspended vertically in organ baths of Krebs solution. The mechanical activity of the isolated ileal longitudinal muscle was recorded. Different substances were added, and the changes produced on spontaneous contraction were recorded. We found that SNP produced significant decrease, while nitric oxide synthase inhibitor produced significant increase in the amplitude of spontaneous contractions. Both apamin, the Ca2+-dependent K+ channel blocker, and methylene blue, the inhibitor of soluble guanylate cyclase, alone, partially decreased relaxation induced by SNP. Addition of both methylene blue and apamine together abolished the inhibitory effect produced by SNP on spontaneous contractions. Nifedipine produced significant decrease in the amplitude of spontaneous contractions. In conclusion, in longitudinal muscle of rabbit ileum, calcium channels blocker are potent inhibitors of spontaneous activity. However, both extracellular and intracellular Ca2+ participates in the spontaneous contractions. NO also has inhibitory effect on spontaneous activity, and this effect is mediated by cGMP generation system and Ca2+-dependent K+ channels.  相似文献   

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