The Experts below are selected from a list of 18351 Experts worldwide ranked by ideXlab platform
Julian I Schroeder - One of the best experts on this subject based on the ideXlab platform.
-
calcium activated k channels and calcium induced calcium release by slow vacuolar ion channels in guard Cell Vacuoles implicated in the control of stomatal closure
The Plant Cell, 1994Co-Authors: John M Ward, Julian I SchroederAbstract:Stomatal closing requires the efflux of K+ from the large vacuolar organelle into the cytosol and across the plasma membrane of guard Cells. More than 90% of the K+ released from guard Cells during stomatal closure originates from the guard Cell Vacuole. However, the corresponding molecular mechanisms for the release of K+ from guard Cell Vacuoles have remained unknown. Rises in the cytoplasmic Ca2+ concentration have been shown to trigger ion efflux from guard Cells, resulting in stomatal closure. Here, we report a novel type of largely voltage-independent K+-selective ion channel in the vacuolar membrane of guard Cells that is activated by physiological increases in the cytoplasmic Ca2+ concentration. These vacuolar K+ (VK) channels had a single channel conductance of 70 pS with 100 mM KCI on both sides of the membrane and were highly selective for K+ over NH4+ and Rb+. Na+, Li+, and Cs+ were not measurably permeant. The Ca2+, voltage, and pH dependences, high selectivity for K+, and high density of VK channels in the vacuolar membrane of guard Cells suggest a central role for these K+ channels in the initiation and control of K+ release from the Vacuole to the cytoplasm required for stomatal closure. The activation of K+-selective VK channels can shift the vacuolar membrane to more positive potentials on the cytoplasmic side, sufficient to activate previously described slow vacuolar cation channels (SV-type). Analysis of the ionic selectivity of SV channels demonstrated a Ca2+ over K+ selectivity (permeability ratio for Ca2+ to K+ of ~3:1) of these channels in broad bean guard Cells and red beet Vacuoles, suggesting that SV channels play an important role in Ca2+-induced Ca2+ release from the Vacuole during stomatal closure. A model is presented suggesting that the interaction of VK and SV channel activities is crucial in regulating vacuolar K+ and Ca2+ release during stomatal closure. Furthermore, the possibility that the ubiquitous SV channels may represent a general mechanism for Ca2+-induced Ca2+ release from higher plant Vacuoles is discussed.
John M Ward - One of the best experts on this subject based on the ideXlab platform.
-
calcium activated k channels and calcium induced calcium release by slow vacuolar ion channels in guard Cell Vacuoles implicated in the control of stomatal closure
The Plant Cell, 1994Co-Authors: John M Ward, Julian I SchroederAbstract:Stomatal closing requires the efflux of K+ from the large vacuolar organelle into the cytosol and across the plasma membrane of guard Cells. More than 90% of the K+ released from guard Cells during stomatal closure originates from the guard Cell Vacuole. However, the corresponding molecular mechanisms for the release of K+ from guard Cell Vacuoles have remained unknown. Rises in the cytoplasmic Ca2+ concentration have been shown to trigger ion efflux from guard Cells, resulting in stomatal closure. Here, we report a novel type of largely voltage-independent K+-selective ion channel in the vacuolar membrane of guard Cells that is activated by physiological increases in the cytoplasmic Ca2+ concentration. These vacuolar K+ (VK) channels had a single channel conductance of 70 pS with 100 mM KCI on both sides of the membrane and were highly selective for K+ over NH4+ and Rb+. Na+, Li+, and Cs+ were not measurably permeant. The Ca2+, voltage, and pH dependences, high selectivity for K+, and high density of VK channels in the vacuolar membrane of guard Cells suggest a central role for these K+ channels in the initiation and control of K+ release from the Vacuole to the cytoplasm required for stomatal closure. The activation of K+-selective VK channels can shift the vacuolar membrane to more positive potentials on the cytoplasmic side, sufficient to activate previously described slow vacuolar cation channels (SV-type). Analysis of the ionic selectivity of SV channels demonstrated a Ca2+ over K+ selectivity (permeability ratio for Ca2+ to K+ of ~3:1) of these channels in broad bean guard Cells and red beet Vacuoles, suggesting that SV channels play an important role in Ca2+-induced Ca2+ release from the Vacuole during stomatal closure. A model is presented suggesting that the interaction of VK and SV channel activities is crucial in regulating vacuolar K+ and Ca2+ release during stomatal closure. Furthermore, the possibility that the ubiquitous SV channels may represent a general mechanism for Ca2+-induced Ca2+ release from higher plant Vacuoles is discussed.
Enid A C Macrobbie - One of the best experts on this subject based on the ideXlab platform.
-
evidence for a role for protein tyrosine phosphatase in the control of ion release from the guard Cell Vacuole in stomatal closure
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Enid A C MacrobbieAbstract:Protein tyrosine phosphatases (PTPases) exist in plants, but their role in plant signaling processes is unknown. One of the most important signaling networks in plants concerns the regulation of stomatal aperture, by which closure of stomatal pores restricts water loss in dry conditions, a process essential for plant survival. Closure is achieved by reduction in guard Cell volume as a consequence of net efflux of potassium salt at both plasmalemma and tonoplast. To test whether protein tyrosine phosphorylation has any role in guard Cell signaling processes, the effects on stomatal aperture and on guard Cell K(Rb) fluxes of a number of specific inhibitors of PTPases have been investigated. Stomatal closure induced by abscisic acid, high external Ca2+, hydrogen peroxide, and dark were all prevented by one such inhibitor, phenylarsine oxide, which added to closed stomata promoted reopening. Flux measurements with 86Rb+ identified the efflux across the tonoplast as the sensitive process, implying that protein tyrosine dephosphorylation must occur at or downstream of the Ca2+ signal responsible for triggering ion efflux from the Vacuole. There was no inhibition of efflux at the plasmalemma. A second inhibitor of PTPases, 3,4 dephosphatin, gave very similar effects, inhibiting closure induced by abscisic acid, high external Ca2+, and dark, and promoting reopening if added to closed stomata. Again, the efflux of K(Rb) at the tonoplast was the sensitive process. These results provide clear evidence for the involvement of PTPases in a major signaling network in plants.
Daniel Reisen - One of the best experts on this subject based on the ideXlab platform.
-
new insights into the tonoplast architecture of plant Vacuoles and vacuolar dynamics during osmotic stress
BMC Plant Biology, 2005Co-Authors: Francis Marty, Daniel Reisen, Nathalie LeborgnecastelAbstract:The vegetative plant Vacuole occupies >90% of the volume in mature plant Cells. Vacuoles play fundamental roles in adjusting Cellular homeostasis and allowing Cell growth. The composition of the Vacuole and the regulation of its volume depend on the coordinated activities of the transporters and channels localized in the membrane (named tonoplast) surrounding the Vacuole. While the tonoplast protein complexes are well studied, the tonoplast itself is less well described. To extend our knowledge of how the Vacuole folds inside the plant Cell, we present three-dimensional reconstructions of Vacuoles from tobacco suspension Cells expressing the tonoplast aquaporin fusion gene BobTIP26-1::gfp. 3-D reconstruction of the Cell Vacuole made possible an accurate analysis of large spanning folds of the vacuolar membrane under both normal and stressed conditions, and suggested interactions between surrounding plastids. Dynamic, high resolution 3-D pictures of the Vacuole in tobacco suspension Cells monitored under different growth conditions provide additional details about vacuolar architecture. The GFP-decorated Vacuole is a single continuous compartment transected by tubular-like transvacuolar strands and large membrane surfaces. Cell culture under osmotic stress led to a complex vacuolar network with an increased tonoplast surface area. In-depth 3-D realistic inspections showed that the unity of the Vacuole is maintained during acclimation to osmotic stress. Vacuolar unity exhibited during stress adaptation, coupled with the intimate associations of Vacuoles with other organelles, suggests a physiological role for the Vacuole in metabolism, and communication between the Vacuole and organelles, respectively, in plant Cells. Desiccation stress ensuing from PEG treatment generates "double" membrane structures closely linked to the tonoplast within the Vacuole. These membrane structures may serve as membrane reservoirs for membrane reversion when Cells are reintroduced to normal growth conditions. 3-D processing of a GFP-labeled tonoplast provides compelling visual constructions of the plant Cell Vacuole and elaborates on the nature of tonoplast folding and architecture. Furthermore, these methods allow real-time determination of membrane rearrangements during stresses.
Ryogo Hirata - One of the best experts on this subject based on the ideXlab platform.
-
patch clamp studies on v type atpase of vacuolar membrane of haploid saccharomyces cerevisiae preparation and utilization of a giant Cell containing a giant Vacuole
Journal of Biological Chemistry, 1999Co-Authors: Isamu Yabe, Kenichi Horiuchi, Katsumi Nakahara, Tetsuo Hiyama, Tadae Yamanaka, Pichao Wang, Kiyoshi Toda, Aiko Hirata, Yoshinori Ohsumi, Ryogo HirataAbstract:Abstract A method for obtaining giant protoplasts ofEscherichia coli (the spheroplast incubation (SI) method: Kuroda et al. (Kuroda, T., Okuda, N., Saitoh, N., Hiyama, T., Terasaki, Y., Anazawa, H., Hirata, A., Mogi, T., Kusaka, I., Tsuchiya, T., and Yabe, I. (1998) J. Biol. Chem. 273, 16897–16904) was adapted to haploid Cells of Saccharomyces cerevisiae. The yeast Cell grew to become as large as 20 μm in diameter and to contain an oversized Vacuole inside. A patch clamp technique in the whole Cell/Vacuole recording mode was applied for the Vacuole isolated by osmotic shock. At zero membrane potential, ATP induced a strong current (as high as 100 pA; specific activity, 0.1 pA/μm2) toward the inside of the Vacuole. Bafilomycin A1, a specific inhibitor of the V-type ATPase, strongly inhibited the activity (K i = 10 nm). Complete inhibition at higher concentrations indicated that any other ATP-driven transport systems were not expressed under the present incubation conditions. This current was not observed in the Vacuoles prepared from a mutant that disrupted a catalytic subunit of the V-type ATPase (RH105(Δvma1::TRP)). TheK m value for the ATP dose response of the current was 159 μm and the H+/ATP ratio estimated from the reversible potential of the V-I curve was 3.5 ± 0.3. These values agreed well with those previously estimated by measuring the V-type ATPase activity biochemically. This method can potentially be applied to any type of ion channel, ion pump, and ion transporter inS. cerevisiae, and can also be used to investigate gene functions in various organisms by using yeast Cells as hosts for homologous and heterogeneous expression systems.