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1.
膜联蛋白是一类同源的水溶性多功能蛋白,可以在依赖和不依赖Ca 2+的环境下与内膜和质膜结合或形成跨膜结构,存在于部分原核生物以及全部的真核生物中,在大多数高等生物中以多基因家族形式存在。植物膜联蛋白在结构上通常只有第1和第4个重复单元是保守的;在功能上可以与细胞骨架结合,具有过氧化物酶活性、核酸水解酶活性和离子通道功能,参与响应盐、干旱、高低温、重金属、损伤等非生物胁迫以及真菌、病虫害等生物胁迫。膜联蛋白基因在植物体的大部分器官及整个生育期均有表达,并且表达量随着植株发育和内外环境的改变而变化,在植物的抗逆性反应中起重要作用。该文对近年来国内外有关植物膜联蛋白的结构和功能,尤其是其在植物逆境生理方面的相关研究进行综述,以期为植物膜联蛋白的深入研究和植物抗逆研究提供思路。 相似文献
2.
Cotton plant is one of the most important economic crops in the world which supplies natural fiber for textile industry. The crucial traits of cotton fiber quality are fiber length and strength, which are mostly determined by the fiber elongation stage. Annexins are assumed to be involved in regulating fiber elongation, but direct evidences remain elusive. Recently, we have investigated the activities of fiber-specific expressed annexins AnGb5/6 and their interacted proteins in cotton. AnGb5 and 6 can interact reciprocally to generate a protein macro-raft in cell membrane. This macro-raft is probably a stabilized scaffold for Actin1 organization. The actin assembling direction and density are correlated with AnGb6 gene expression and fiber expanding rate among three fiber length genotypes. These results suggest that annexins may act as the adaptor that linked fiber cell membrane to actin assembling. Due to the strong Ca 2+ and lipid binding ability of annexins, these results also indicate that annexins complex may function as an intermediate to receive Ca 2+ or lipid signals during fiber elongation. 相似文献
3.
Abstract The role of calcium during the synthesis, secretion and molecular organization of the primary cell-wall polysaccharides is the topic of this review. With the exception of callose synthase, the in vitro activity of all polysaccharide synthases is not controlled by Ca 2+ ions. However, changes in the intracellular Ca 2+ level could control the rate of exocytotic fusion of the secretory vesicles containing cell-wall matrix polysaccharides. In particular, the ability of Ca 2+ to regulate the fusion of secretory vesicles with the plasma membrane is due to a class of Ca 2+-dependent phospholipid-binding proteins known as annexins. The ionic interactions between calcium and the negatively charged homogalacturonan domains of the pectins are important not only for the mechanical properties of the wall but also for the gel-properties of these complex biopolymers. 相似文献
4.
AbstractAnnexins are physiologically important proteins that play a role in calcium buffering but also influence membrane structure, participate in Ca 2+-dependent membrane repair events and in remodelling of the cytoskeleton. Thirty years ago several peptides isolated from lung perfusates, peritoneal leukocytes, neutrophiles and renal cells were proven inhibitory to the activity of phospholipase A 2. Those peptides were found to derive from structurally related proteins: annexins AnxA1 and AnxA2. These findings raised the question whether annexins may participate in regulation of the production of lipid second messengers and, therefore, modulate numerous lipid mediated signaling pathways in the cell. Recent advances in the field of annexins made also with the use of knock-out animal models revealed that these proteins are indeed important constituents of specific signaling pathways. In this review we provide evidence supporting the hypothesis that annexins, as membrane-binding proteins and organizers of the membrane lateral heterogeneity, may participate in lipid mediated signaling pathways by affecting the distribution and activity of lipid metabolizing enzymes (most of the reports point to phospholipase A 2) and of protein kinases regulating activity of these enzymes. Moreover, some experimental data suggest that annexins may directly interact with lipid metabolizing enzymes and, in a calcium-dependent or independent manner, with some of their substrates and products. On the basis of these observations, many investigators suggest that annexins are capable of linking Ca 2+, redox and lipid signaling to coordinate vital cellular responses to the environmental stimuli. 相似文献
5.
We have examined the characteristics of Ca 2+-dependent phospholipid-binding proteins (annexins) in maize ( Zea mays L.) coleoptiles and tip-growing pollen tubes of Lilium longiflorum. In maize, there are three such proteins, p35, p33, and p23. Partial sequence analysis reveals that peptides from p35 and p33 have identity to members of the annexin family of animal proteins and to annexins from tomato. Interestingly, multiple sequence alignments reveal that the domain responsible for Ca 2+ binding in animal annexins is not conserved in these plant peptide sequences. Although p33 and p35 share the annexin characteristic of binding to membrane lipid, unlike annexins II and VI they do not associate with detergent-insoluble cytoskeletal proteins or with F-actin from either plants or animals. Immunoblotting with antiserum raised to p33/p35 from maize reveals that cross-reactive polypeptides of 33 to 35 kilodaltons are also present in protein extracts from pollen tubes of L. longiflorum. Immunolocalization at the light microscope level suggests that these proteins are predominantly confined to the nongranular zone at the tube tip, a region rich in secretory vesicles. Our hypothesis that plant annexins mediate exocytotic events is supported by the finding that p23, p33, and p35 bind to these secretory vesicles in a Ca 2+-dependent manner. 相似文献
6.
The annexins are a family of Ca 2+- and phospholipid-binding proteins, which interact with membranes upon increase of [Ca 2+] i or during cytoplasmic acidification. The transient nature of the membrane binding of annexins complicates the study of their influence on intracellular processes. To address the function of annexins at the plasma membrane (PM), we fused fluorescent protein-tagged annexins A6, A1, and A2 with H- and K-Ras membrane anchors. Stable PM localization of membrane-anchored annexin A6 significantly decreased the store-operated Ca 2+ entry (SOCE), but did not influence the rates of Ca 2+ extrusion. This attenuation was specific for annexin A6 because PM-anchored annexins A1 and A2 did not alter SOCE. Membrane association of annexin A6 was necessary for a measurable decrease of SOCE, because cytoplasmic annexin A6 had no effect on Ca 2+ entry as long as [Ca 2+] i was below the threshold of annexin A6-membrane translocation. However, when [Ca 2+] i reached the levels necessary for the Ca 2+-dependent PM association of ectopically expressed wild-type annexin A6, SOCE was also inhibited. Conversely, knockdown of the endogenous annexin A6 in HEK293 cells resulted in an elevated Ca 2+ entry. Constitutive PM localization of annexin A6 caused a rearrangement and accumulation of F-actin at the PM, indicating a stabilized cortical cytoskeleton. Consistent with these findings, disruption of the actin cytoskeleton using latrunculin A abolished the inhibitory effect of PM-anchored annexin A6 on SOCE. In agreement with the inhibitory effect of annexin A6 on SOCE, constitutive PM localization of annexin A6 inhibited cell proliferation. Taken together, our results implicate annexin A6 in the actin-dependent regulation of Ca 2+ entry, with consequences for the rates of cell proliferation.Calcium entry into cells either through voltage- or receptor-operated channels, or following the depletion of intracellular stores is a major factor in maintaining intracellular Ca 2+ homeostasis. Resting [Ca 2+] i is low (∼100 n m compared with extracellular [Ca 2+] ex of 1.2 m m) and can be rapidly increased by inositol triphosphate-mediated release from the intracellular Ca 2+ stores (mostly endoplasmic reticulum (ER) 3), or by channel-mediated influx across the plasma membrane (PM). Store-operated calcium entry (SOCE) has been proposed as the main process controlling Ca 2+ entry in non-excitable cells ( 1), and the recent discovery of Orai1 and STIM provided the missing link between the Ca 2+-release activated current (I CRAC) and the ER Ca 2+ sensor ( 2– 4). Translocation of STIM within the ER, accumulation in punctae at the sites of contact with PM and activation of Ca 2+ channels have been proposed as a model of its regulation of Orai1 activity ( 5, 6). However, many details of the functional STIM-Orai1 protein complex and its regulation remain to be elucidated. The actin cytoskeleton plays a major role in the regulation of SOCE, possibly by influencing the function of ion channels or by interfering with the interaction between STIM and Orai1 ( 7– 9). However, the proteins connecting the actin cytoskeleton and SOCE activity at the PM have yet to be identified.The annexins are a multigene family of Ca 2+- and phospholipid-binding proteins, which have been implicated in many Ca 2+-regulated processes. Their C-terminal core is evolutionarily conserved and contains Ca 2+-binding sites, their N-terminal tails are unique and enable the protein to interact with distinct cytoplasmic partners. At low [Ca 2+] i, annexins are diffusely distributed throughout the cytosol, however, after stimulation resulting in the increase of [Ca 2+] i, annexins are targeted to distinct subcellular membrane locations, such as the PM, endosomes, or secretory vesicles ( 10). Annexins are involved in the processes of vesicle trafficking, cell division, apoptosis, calcium signaling, and growth regulation ( 11), and frequent changes in expression levels of annexins are observed in disease ( 12, 13). Previously, using biochemical methods and imaging of fluorescent protein-tagged annexins in live cells, we demonstrated that annexins A1, A2, A4, and A6 interacted with the PM as well as with internal membrane systems in a highly coordinated manner ( 10, 14). In addition, there is evidence of Ca 2+-independent membrane association of several annexins, including annexin A6 ( 15– 19); some of which point to the existence of pH-dependent binding mechanisms ( 20– 22). Given the fact that several annexins are present within any one cell, it is likely that they form a [Ca 2+] and pH sensing system, with a regulatory influence on other signaling pathways.The role of annexins as regulators of ion channel activity has been addressed previously ( 23– 25). In particular, annexin A6 has been implicated in regulation of the sarcoplasmic reticulum ryanodine-sensitive Ca 2+ channel ( 25), the neuronal K + and Ca 2+ channels ( 26), and the cardiac Na +/Ca 2+ exchanger ( 27). Cardiac-specific overexpression of annexin A6 resulted in lower basal [Ca 2+], a depression of [Ca 2+] i transients and impaired cardiomyocyte contractility ( 28). In contrast, the cardiomyocytes from the annexin A6 null-mutant mice showed increased contractility and accelerated Ca 2+ clearance ( 29). Consistent with its role in mediating the intracellular Ca 2+ signals, especially Ca 2+ influx, ectopic overexpression of annexin A6 in A431 cells, which lack endogenous annexin A6, resulted in inhibition of EGF-dependent Ca 2+ entry ( 30).The difficulty of investigating the influence of annexins on signaling events occurring at the PM lies in the transient and reversible nature of their Ca 2+ and pH-dependent lipid binding. Although the intracellular Ca 2+ increase following receptor activation or Ca 2+ influx promotes the association of the Ca 2+-sensitive annexins A2 and A6 with the PM, the proteins quickly resume their cytoplasmic localization upon restoration of the basal [Ca 2+] i ( 14). Therefore, to investigate the effects of membrane-associated annexins on Ca 2+ homeostasis and the cell signaling machinery, we aimed to develop a model system allowing for a constitutive membrane association of annexins. Here we used the PM-anchoring sequences of the H- and K-Ras proteins to target annexins A6 and A1 to the PM independently of [Ca 2+]. The Ras GTPases are resident at the inner leaflet of the PM and function as molecular switches ( 31). The C-terminal 9 amino acids of H- and N-Ras and the C-terminal 14 amino acids of K-Ras comprise the signal sequences for membrane anchoring of Ras isoforms ( 32). Although the palmitoylation and farnesylation of the C terminus of H-Ras (tH) serves as a targeting signal for predominantly cholesterol-rich membrane microdomains at the PM (lipid rafts/caveolae) ( 33), the polybasic group and the lipid anchor of K-Ras (tK) ensures the association of K-Ras with cholesterol-poor PM membrane domains. Importantly, these minimal C-terminal amino acid sequences are sufficient to target heterologous proteins, for example GFP, to different microdomains at the PM and influence their trafficking ( 34).In the present study we fused annexins A6, A2, and A1 with fluorescent proteins and introduced the PM-anchoring sequences of either H-Ras (annexin-tH) or K-Ras (annexin-tK) at the C termini of the fusion constructs. We demonstrate that the constitutive PM localization of annexin A6 results in down-regulation of store-operated Ca 2+ entry. Expression of membrane-anchored annexin A6 causes an accumulation of the cortical F-actin, and cytoskeletal destabilization with latrunculin A abolishes the inhibitory effect of PM-anchored annexin A6 on SOCE. Taken together, our results implicate annexin A6 in the maintenance of intracellular Ca 2+ homeostasis via actin-dependent regulation of Ca 2+ entry. 相似文献
7.
In vitro phosphorylation of several membrane polypeptides and soluble polypeptides from corn ( Zea mays var. Patriot) coleoptiles was promoted by adding Ca 2+. Ca 2+-promoted phosphorylation of the membrane polypeptides was further increased in the presence of calmodulin. Both Ca 2+-stimulated and Ca 2+- and calmodulin-stimulated phosphorylations of membrane polypeptides were inhibited by chlorpromazine, a calmodulin antagonist. Ca 2+-stimulated phosphorylation of soluble polypeptides increased with increasing Ca 2+ concentration. The calmodulin antagonists chlorpromazine and trifluoperazine inhibited the Ca 2+-promoted phosphorylation of soluble polypeptides. Added calmodulin promoted the Ca 2+-dependent phosphorylation of a 98 kilodaltons polypeptide. Both Ca 2+-dependent and Ca 2+-independent phosphorylations required Mg 2+ at an optimal concentration of 5 to 10 millimolar. Cyclic AMP was found to have no stimulatory effect on protein phosphorylation. Sodium molybdate, an inhibitor of protein phosphatase, increased the net phosphorylation of several polypeptides. Rapid loss of radioactivity from the phosphorylated polypeptides following incubation in unlabeled ATP indicated the presence of phosphoprotein phosphatase activity. 相似文献
8.
There is evidence that Ca 2+ can regulate vesicle-mediated secretion in plant cells, but the mechanism for this is not known. One possibility is that Ca 2+ -dependent phospholipid-binding proteins (annexins) couple the Ca 2+ stimulus to the exocytotic response. Using a protocol developed for the isolation of animal annexins we have identified proteins in maize ( Zea mays L.) coleoptiles that have similar characteristics to annexins. The predominant polypeptide species run as a doublet of relative molecular mass (M r) 33000–35000 on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE); another less-abundant protein of M r 23000 is also present. In the presence of Ca 2+ these proteins bind to liposomes composed of acidic phospholipids. Calcium-sensitivity of binding differs for each protein and is also influenced by the pH of the buffer used for the liposome-binding assay. Antiserum raised to the 33 to 35-kDa doublet purified on SDS-PAGE recognises the doublet in crude extracts from maize and proteins of similar M r in Tradescantia virginiana and tobacco Nicotiana tabacum L. The antiserum also recognises p68 (Annexin VI) from chicken gizzard extracts, indicating homology between animal annexins and the maize proteins. For the maize proteins to be involved in the regulation of exocytosis, binding to phospholipids would be expected to occur at physiological levels of Ca 2+. The characteristics of the maize annexin-like proteins are described and attention drawn to the marked effect of pH in lowering the requirement for Ca 2+ for phospholipid binding.Abbreviations DEAE
diethylaminoethyl
- EGTA
ethylene glycol-bis (-aminoethyiether)-N,N,N,N-tetraacetic acid
- kDa
kilodalton(s)
- M r
relative molecular mass
- SDS-PAGE
sodium dodecyl sulphate-polyacrylamide gel electrophoresis
This work was funded by the Agricultural and Food Research Council. Our thanks also to Professor P. Lowry and Dr R. Woods, Department of Biochemistry, University of Reading for facilities and advice for antiserum production, and C. Boustead, Department of Biochemistry, University of Leeds for advice on immunoblotting and phospholipid-binding assays. 相似文献
9.
Plant annexins are Ca 2+-dependent phospholipid-binding proteins and are encoded by multigene families. They are implicated in the regulation of plant
development as well as protection from drought and other stresses. They are well characterized in Arabidopsis, however no such characterization of rice annexin gene family has been reported thus far. With the availability of the rice
genome sequence information, we have identified ten members of the rice annexin gene family. At the protein level, they share
16–64% identity with predicted molecular masses ranging from 32 to 40 kDa. Phylogenetic analysis of rice annexins together
with annexins from other monocots led to their classification into five different orthologous groups and share similar motif
patterns in their protein sequences. Expression analysis by real-time RT-PCR revealed differential temporal and spatial regulation
of these genes. The rice annexin genes are also found to be regulated in seedling stage by various abiotic stressors including
salinity, drought, heat and cold. Additionally, in silico analysis of the putative upstream sequences was analyzed for the
presence of stress-responsive cis-elements. These results provide a basis for further functional characterization of specific rice annexin genes at the tissue/developmental
level and in response to abiotic stresses. 相似文献
10.
The Rem, Rem2, Rad, and Gem/Kir (RGK) GTPases, comprise a subfamily of small Ras-related GTP-binding proteins, and have been shown to potently inhibit high voltage-activated Ca 2+ channel current following overexpression. Although the molecular mechanisms underlying RGK-mediated Ca 2+ channel regulation remains controversial, recent studies suggest that RGK proteins inhibit Ca 2+ channel currents at the plasma membrane in part by interactions with accessory channel β subunits. In this paper, we extend our understanding of the molecular determinants required for RGK-mediated channel regulation by demonstrating a direct interaction between Rem and the proximal C-terminus of Ca V1.2 (PCT), including the CB/IQ domain known to contribute to Ca 2+/calmodulin (CaM)-mediated channel regulation. The Rem2 and Rad GTPases display similar patterns of PCT binding, suggesting that the Ca V1.2 C-terminus represents a common binding partner for all RGK proteins. In vitro Rem:PCT binding is disrupted by Ca 2+/CaM, and this effect is not due to Ca 2+/CaM binding to the Rem C-terminus. In addition, co-overexpression of CaM partially relieves Rem-mediated L-type Ca 2+ channel inhibition and slows the kinetics of Ca 2+-dependent channel inactivation. Taken together, these results suggest that the association of Rem with the PCT represents a crucial molecular determinant in RGK-mediated Ca 2+ channel regulation and that the physiological function of the RGK GTPases must be re-evaluated. Rather than serving as endogenous inhibitors of Ca 2+ channel activity, these studies indicate that RGK proteins may play a more nuanced role, regulating Ca 2+ currents via modulation of Ca 2+/CaM-mediated channel inactivation kinetics. 相似文献
11.
Two membrane fractions, one enriched in sarcoplasmic reticulum and the other enriched in sarcolemma, were isolated from the myocardium of young (3–4-months-old) and aged (24–25-months old) rats. ATP-supported Ca 2+ binding and accumulating activities as well as (Mg 2+ + Ca 2+)-ATPase activities of these membrane fractions were studied in an effort to determine the influence of age on the Ca 2+ pump function of the two myocardial membrane systems. Sarcoplasmic reticulum from aged hearts showed significantly reduced (approx. 50%) rates of ATP-supported (oxalate-facilitated) Ca 2+ accumulation compared to sarcoplasmic reticulum from young hearts; the amount of Ca 2+ accumulated by this membrane of aged heart at steady state was also lower. On the other hand, sarcolemma from aged hearts displayed 2-fold higher rates of ATP-supported Ca 2+ accumulation compared to sarcolemma from young hearts; at steady state, sarcolemma from aged hearts accumulated significantly higher amounts of Ca 2+ than did sarcolemma from young hearts. Similar age-related differences were also observed in the ATP-dependent Ca 2+ binding activities of the two membranes, determined in the absence of oxalate. The divergent age-associated changes in Ca 2+ binding and accumulating activities of sarcoplasmic reticulum and sarcolemma were seen at varying Ca 2+ concentrations (0.24–39.1 μM).With either membrane, kinetic analysis showed 2-fold age-related differences in the V values for ATP-supported Ca 2+ accumulation ( V (nmol Ca 2+/mg protein per min): sarcoplasmic reticulum — young, 119 ± 8; aged, 59 ± 5; sarcolemma — young, 11 ± 2; aged, 21 ± 3); the concentrations of Ca 2+ required for half-maximal velocities did not differ significantly with age ( K0.5 for Ca 2+ (μM): sarcoplasmic reticulum — young, 2.5 ± 0.20; aged, 2.9 ± 0.25; sarcolemma — yount, 2.7 ± 0.25; aged, 3.2 ± 0.30). Kinetic parameters of ATP-dependent Ca 2+ binding also indicated that the velocity of Ca 2+ binding but not the concentration of Ca 2+ required for half-maximal binding was altered due to aging. At identical Ca 2+ concentrations, the combined Ca 2+ accumulating activity of sarcoplasmic reticulum and sarcolemma from aged hearts was significantly lower (38–47%) than the combined Ca 2+ accumulating activity of the two membranes from young hearts. No significant age-related differences were observed in the ATP-independent (passive) Ca 2+ binding (or accumulation) by sarcoplasmic reticulum and sarcolemma, the (Mg 2+ + Ca 2+)-ATPase activities of these membranes, their polypeptide composition or relative purity. These results indicate that differential alterations occur in the ATP-supported Ca 2+ pump activities of sarcoplasmic reticulum and sarcolemma in aging myocardium and such alterations may be due to age-associated changes in the efficacy of coupling ATP hydrolysis to Ca 2+ transport. Further, the age-related increment in the Ca 2+ pump activity of sarcolemma is inadequate to fully compensate for the diminished Ca 2+ pump activity of sarcoplasmic reticulum. It is, therefore, suggested that deterioration of the Ca 2+ pump function of sarcoplasmic reticulum may contribute to the increased relaxation time observed in aging heart. 相似文献
12.
Summary The haemolysin protein (HlyA) of Escherichia coli contains 11 tandemly repeated sequences consisting of 9 amino acids each between amino acids 739 and 849 of HlyA. We removed, by oligonucleotide-directed mutagenesis, different single repeats and combinations of several repeats. The resulting mutant proteins were perfectly stable in E. coli and were secreted with the same efficiency as the wild-type HlyA. HlyA proteins which had lost a single repeat only were still haemolytically active (in the presence of HlyC) but required elevated levels of Ca 2+ for activity, as compared to the wild-type haemolysin. Removal of three or more repeats led to the complete loss of the haemolytic activity even in the presence of high Ca 2+ concentrations. The mutant haemolysins were unable to compete with the wild-type haemolysin for binding to erythrocytes at low Ca 2+ concentrations but could still generate ion-permeable channels in artificial lipid bilayer membranes formed of plant asolectin, even in the complete absence of Ca 2+. These data indicate that the repeat domain of haemolysin is responsible for Ca 2+-dependent binding of haemolysin to the erythrocyte membrane. A model for the possible functional role of Ca 2+ in haemolysis is presented. 相似文献
13.
Calcium (Ca 2+) signals are essential transducers and regulators in many adaptive and developmental processes in plants. Protective responses of plants to a variety of environmental stress factors are mediated by transient changes of Ca 2+ concentration in plant cells. Ca 2+ ions are quickly transported by channel proteins present on the plasma membrane. During responses to external stimuli, various signal molecules are transported directly from extracellular to intracellular compartments via Ca 2+ channel proteins. Three types of Ca 2+ channels have been identified in plant cell membranes: voltage-dependent Ca 2+-permeable channels (VDCCs), which is sorted to depolarization-activated Ca 2+-permeable channels (DACCs) and hyperpolarization-activated Ca 2+-permeable channels (HACCs), voltage-independent Ca 2+-permeable channels (VICCs). They make functions in the abiotic stress such as TPCs, CNGCs, MS channels, annexins which distribute in the organelles, plasma membrane, mitochondria, cytosol, intracelluar membrane. This review summarizes recent advances in our knowledge of many types of Ca 2+ channels and Ca 2+ signals involved in abiotic stress resistance and responses in plant cells. 相似文献
14.
In cells of Zea mays (root hairs, coleoptiles) and Riccia fluitans (rhizoids, thalli) intracellular Ca 2+ and pH have been measured with double-barrelled microelectrodes. Free Ca 2+ activities of 109–187 nM ( Riccia rhizoids), 94–160 nM ( Riccia thalli), 145–231 nM ( Zea root hairs), 84–143 nM ( Zea coleoptiles) were found, and therefore identified as cytoplasmic. In a few cases ( Riccia rhizoids), free Ca 2+ was in the lower millimolar range (2.3±0.8 mM). A change in external Ca 2+ from 0.1 to 10 mM caused an initial and short transient increase in cytoplasmic free Ca 2+ which finally levelled off at about 0.2 pCa unit below the control, whereas in the presence of cyanide the Ca 2+ activity returned to the control level. It is suggested that this behaviour is indicative of active cellular Ca 2+ regulation, and since it is energy-dependent, may involve a Ca 2+-ATPase. Acidification of the cytoplasmic pH and alkalinization of the vacuolar pH lead to a simultaneous increase in cytoplasmic free Ca 2+, while alkalinization of pH c decreased the Ca 2+ activity. Since this is true for such remote organisms as Riccia and Zea, it may be concluded that regulation of cytoplasmic pH and free Ca 2+ are interrelated. It is further concluded that double-barrelled microelectrodes are useful tools for investigations of intracellular ion activities in plant cells.Symbols and abbreviations m, m
membrane potential difference, changes thereof
- PVC
polyvinylchloride 相似文献
15.
Background information. Spermatozoa show several changes in flagellar waveform, such as upon fertilization. Ca 2+ has been shown to play critical roles in modulating the waveforms of sperm flagella. However, a Ca 2+‐binding protein in sperm flagella that regulates axonemal dyneins has not been fully characterized. Results. We identified a novel neuronal calcium sensor family protein, named calaxin (Ca 2+‐binding axonemal protein), in sperm flagella of the ascidian Ciona intestinalis. Calaxin has three EF‐hand Ca 2+‐binding motifs, and its orthologues are present in metazoan species, but not in yeast, green algae or plant. Immunolocalization revealed that calaxin is localized near the outer arm of the sperm flagellar axonemes. Moreover, it is distributed in adult tissues bearing epithelial cilia. An in vitro binding experiment indicated that calaxin binds to outer arm dynein. A cross‐linking experiment showed that calaxin binds to β‐tubulin in situ. Overlay experiments further indicated that calaxin binds the β‐dynein heavy chain of outer arm dynein in the presence of Ca 2+. Conclusions. These results suggest that calaxin is a potential Ca 2+‐dependent modulator of outer arm dynein in metazoan cilia and flagella. 相似文献
16.
About 20% of all irrigated land is adversely affected by salinity hazards and therefore understanding plant defense mechanisms against salinity will have great impact on plant productivity. In the last decades, comprehension of salinity resistance at molecular level has been achieved through the identification of key genes encoding biomarker proteins underpinning salinity tolerance. Implication of the vacuolar transport systems in plant salinity tolerance is one example of these central mechanisms rendering tolerance to saline stress. One important organelle in plant cells is the central vacuole that plays pivotal multiple roles in cell functioning under normal and stress conditions. This review thus attempts to address different lines of evidence supporting the role of the vacuolar membrane transport systems in plant salinity tolerance. Vacuolar transport systems include Na+(K+)/H+ antiporters, V-ATPase, V-PPase, Ca2+/H+ exchangers, Ca2+-ATPase, ion channels, aquaporins, and ABC transporters. They contribute essentially in retaining a high cytosolic K+/Na+ ratio, K+ level, sequestrating Na+ and Cl? into vacuoles, as well as regulation of other salinity responsive pathways. However, little is known about the regulation and functions of some of the vacuolar transporters under salinity stress and therefore need more exploration and focus. Numerous studies demonstrated that the activities of the vacuolar transporters are upregulated in response to salinity stress, confirming their central roles in salinity tolerance mechanism. The second line of evidence is that manipulation of one of the genes encoding the vacuolar transport proteins results in some successful improvement of plant salinity tolerance. Therefore, transgene pyramiding of more than one gene for developing genotypes with better and strong salinity tolerance and productivity should gain more attention in future research. In addition, we should move step further and verify the experimental data obtained from either a greenhouse or controlled environment into field trials in order to support our claims. 相似文献
17.
The toxicity of Cd 2+in vivo during the early phases of radish ( Raphanus sativus L.) seed germination and the in vitro Cd 2+ effect on radish calmodulin (CaM) were studied. Cd 2+ was taken up in the embryo axes of radish seeds; the increase in fresh weight of embryo axes after 24 h of incubation was inhibited significantly in the presence of 10 mmol m ?3 Cd 2+ in the external medium, when the Cd 2+ content in the embryo axes was c. 1.1 μmol g ?1 FW. The reabsorption of K +, which characterizes germination, was inhibited by Cd 2+, suggesting that Cd 2+ affected metabolic reactivation. The slight effect of Cd 2+ on the transmembrane electric potential of the cortical cells of the embryo axes excluded a generalized toxicity of Cd 2+ at the plasma membrane level. After 24 h of incubation, Cd 2+ induced no increase in total acid-soluble thiols and Cd 2+-binding peptides able to reduce Cd 2+ toxicity. Ca 2+ added to the incubation medium partially reversed the Cd 2+-induced inhibition of the increase in fresh weight of embryo axes and concomitantly reduced Cd 2+ uptake. Equilibrium dialysis experiments indicated that Cd 2+ bound to CaM and competed with Ca 2+ in this binding. Cd 2+ inhibited the activation of Ca 2+-CaM-dependent calf-brain phosphodiesterase, inhibiting the Ca 2+-CaM active complex. Cd 2+ reduced the binding of CaM to the Ca 2+-CaM binding enzymes present in the soluble fraction of the embryo axes of radish seeds. The possibility that Cd 2+ toxicity in radish seed germination is mediated by the action of Cd 2+ on Ca 2+-CaM is discussed in relation to the in vivo and in vitro effects of Cd 2+. 相似文献
18.
The Na +/Ca 2+ exchanger provides a major Ca 2+ extrusion pathway in excitable cells and plays a key role in the control of intracellular Ca 2+ concentrations. In Canis familiaris, Na +/Ca 2+ exchanger (NCX) activity is regulated by the binding of Ca 2+ to two cytosolic Ca 2+‐binding domains, CBD1 and CBD2, such that Ca 2+‐binding activates the exchanger. Despite its physiological importance, little is known about the exchanger's global structure, and the mechanism of allosteric Ca 2+‐regulation remains unclear. It was found previously that for NCX in the absence of Ca 2+ the two domains CBD1 and CBD2 of the cytosolic loop are flexibly linked, while after Ca 2+‐binding they adopt a rigid arrangement that is slightly tilted. A realistic model for the mechanism of the exchanger's allosteric regulation should not only address this property, but also it should explain the distinctive behavior of Drosophila melanogaster's sodium/calcium exchanger, CALX, for which Ca 2+‐binding to CBD1 inhibits Ca 2+ exchange. Here, NMR spin relaxation and residual dipolar couplings were used to show that Ca 2+ modulates CBD1 and CBD2 interdomain flexibility of CALX in an analogous way as for NCX. A mechanistic model for the allosteric Ca 2+ regulation of the Na +/Ca 2+ exchanger is proposed. In this model, the intracellular loop acts as an entropic spring whose strength is modulated by Ca 2+‐binding to CBD1 controlling ion transport across the plasma membrane. Proteins 2016; 84:580–590. © 2016 Wiley Periodicals, Inc. 相似文献
19.
The capacity of symbiosomes from yellow lupin root nodules for active Ca 2+uptake and the sensitivity of their nitrogenase activity to a disturbance of the symbiotic Ca partition were investigated. The experiments carried out on the isolated symbiosomes and the peribacteroid membrane (PBM) vesicles, using Ca 2+indicators arsenazo III and chlorotetracycline, and the cytochemical Ca visualization with potassium pyroantimonate (PA) provided evidence that an Mg-ATP-energized pump, most likely Mg 2+-dependent Ca 2+-ATPase catalyzing the active transport of Ca 2+from the cytosol of the plant cell into the symbiosomes across the PBM, functions on this membrane. Depleting the symbiosomes of Ca both in vivoand in vitroby treating the intact nodules of yellow lupin root or the purified symbiosomes isolated from the latter with EGTA and Ca 2+-ionophore A23187 substantially decreased their nitrogenase activity. The inhibitory effect of calcium deficit in the symbiosomes was not reversed by the addition of calcium to the incubation medium containing the plant tissues under study and was even enhanced under these conditions. The nitrogenase activity of the isolated symbiosomes not experiencing calcium deficit was also inhibited by the addition of relatively high concentrations of exogenous calcium to the incubation medium. These results seem to give evidence that the calcium status of nodule symbiosomes from yellow lupin roots controls their nitrogenase activity. The data obtained suggest that both Ca 2+transport on PBM and the low passive permeability of this membrane for the given cation play the key role in such a control. 相似文献
20.
Summary The control by nucleotides of the Ca 2+-activated channel which regulates the nonspecific permeability of the mitochondrial inner membrane has been investigated quantitatively. The cooperative binding of two molecules of ADP to the internal (matrix) side of the channel causes a mixed-type inhibition of channel activity. ATP, AMP, cAMP and GDP are all ineffective. NADH shows a pattern of inhibition similar to that of ADP, though the apparent K
I is higher by a factor of 200. NADPH relieves the inhibition by NADH. NAD + also inhibits, but its affinity is a factor of 10 less than that of NADH. When ADP and NADH are added together, they act synergistically to inhibit the Ca 2+-activated channel. It is concluded that the concept of the modification of enzyme activity by the allosteric binding of nucleotides, which is well established for soluble enzyme systems, also has application to the regulation of channels that control membrane permeability. 相似文献
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