Exploring Biophysical and Biochemical Components of the Osmotic Motor that Drives Stomatal Movement*

Raschke, Klaus; Hedrich, Rainer; Reckmann, Udo; Schroeder, Julian I.

doi:10.1111/j.1438-8677.1988.tb00046.x

Cited by 92 publications

(76 citation statements)

References 49 publications

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“…In a guard cell of this species, Rubisco had a capacity to carboxylate RuBP at a rate ofapproximately 115 fmol cell-' h-'. The capacity of PEP carboxylase was much higher and depended strongly on pH (18). At pH 8, the in vitro activity was 1000 fmol cell-' h-'; at pH 7.1, which presumably resembled the cytoplasmic value, it was about 500 fmol cell-' h-'.…”

Section: Discussionmentioning

confidence: 94%

“…If the reductive pentose-phosphate path in guard cells produced a similar distribution, the average share of 54% phosphorylated compounds in these protoplasts would extrapolate to an in vivo activity of 16 fmol cell-' h-' (54/89 of the average fixation rate of 27 fmol cell-' h-' during a 2 spulse; Table II). Relative to Chl content (0.9 pg cell-'), the in vitro activity was 131 gmol (mg Chl)' h-', and the estimated in vivo activity was 18 ,umol (mg Chl)' h-'. This in vivo rate is close to the Rubisco activity of 22 ,umol (mg Chl)' h-' which we derived from the data of Gotow et al (4) for guard cells of V. faba, in the way indicated above.…”

Section: Discussionmentioning

confidence: 95%

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Rubisco Activity in Guard Cells Compared with the Solute Requirement for Stomatal Opening

Reckmann¹,

Scheibe²,

Raschke³

1990

Plant Physiol.

110

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We investigated whether the reductive pentose phosphate path in guard cells of Pisum sativum had the capacity to contribute significantly to the production of osmotica during stomatal opening in the light. Amounts of ribulose 1,5-bisphophate carboxylase/ oxygenase (Rubisco) were determined by the [14C]carboxyarabinitol bisphosphate assay. A guard cell contained about 1.2 and a mesophyll cell about 324 picograms of the enzyme; the ratio was 1:270. The specific activities of Rubisco in guard cells and in mesophyll cells were equal; there was no indication of a specific inhibitor of Rubisco in guard cells. Rubisco activity was 115 femtomol per guard-cell protoplast and hour. This value was different from zero with a probability of 0.99. After exposure of guard-cell protoplasts to 14C02 for 2 seconds in the light, about one-half of the radioactivity was in phosphorylated compounds and <10% in malate. Guard cells in epidermal strips produced a different labelling pattern; in the light, <10% of the label was in phosphorylated compounds and about 60% in malate. The rate of solute accumulation in intact guard cells was estimated to have been 900 femto-osmol per cell and hour. If Rubisco operated at full capacity in guard cells, and hexoses were produced as osmotica, solutes could be supplied at a rate of 19 femto-osmol per cell and hour, which would constitute 2% of the estimated requirement. The capacity of guard-cell Rubisco to meet the solute requirement for stomatal opening in leaves of Pisum sativum is insignificant.

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Section: Discussionmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 95%

Rubisco Activity in Guard Cells Compared with the Solute Requirement for Stomatal Opening

Reckmann¹,

Scheibe²,

Raschke³

1990

Plant Physiol.

110

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“…In addition to InsP3-gated Ca2+ release channels (Alexandre et al, 1990;Alexandre and Lassalles, 1992), vacuoles from beet taproots contain voltage-gated Ca2+-selective channels with gating characteristics that suggest a role in vacuolar Ca2+ release (Johannes et al, 1992a(Johannes et al, , 1992bGelli and Blumwald, 1993). Therefore, at least two possible convergence points for discrete primary signals exist, of which activation of either or both would lead to the elevation of Preliminary electrophysiological studies of guard cell vacuoles have been undertaken previously (Hedrich et al, 1988;Raschke et al, 1988). The presence of an H+-ATPase and slow vacuolar (SV) channels were reported, although neither transport system was characterized in detail.…”

Section: Introductionmentioning

confidence: 99%

Two Voltage-Gated, Calcium Release Channels Coreside in the Vacuolar Membrane of Broad Bean Guard Cells

Allen¹,

Sanders²

1994

The Plant Cell

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Voltage-gated, Ca2+ release channels have been characterized at the vacuolar membrane of broad bean guard cells using patch clamps of excised, inside-out membrane patches. The most prevalent Ca2+ release channel had a conductance of 27 pS over voltages negative of the reversal potential(€,ev) (cytosol referenced to vacuole), with 5, 10, or 20 mM Ca2+ as the charge carrier on the vacuolar side and 50 mM K+ on the cytosolic side. The single-channel current saturated at -2.6 pA. The relative permeability of the channel was in the range of a Pcaa+:Ptp ratio of 6:l. Divalent cations could act as charge carriers on the vacuolar.side with a conductance series of Ba2+ > Mg2+ > Sr2+ > Ca2+ and a selectivity sequence of Ca2+ = Ba2+ = Sr2+ > Mg2+. The channel was gated open by cytosol-negative (physiological) transmembrane voltages, increases in vacuolar Ca2+ concentration, and increases in the vacuolar pH. The channel was potently inhibited by the Ca2+ channel blockers Gd3+ (half-maximal inhibition at 10.3 pM) and nifedipine (half-maximal inhibition at 77 pM). The stilbene derivative 4,4'-diisothiocyano9,2'-stilbene disulfonate was also inhibitory (half-maximal inhibition for a 4-min incubation period at 6.3 pM). The 27-pS channel coresides in individual guard cell vacuoles with a less frequently observed 14-pS Ca2+ release channel that had similar, although not identical, voltage dependence and gating characteristics and a lower selectivity for Ca2+ over K+. The requirement for two channels with a similar function at the vacuolar membrane of guard cells is discussed.

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“…This protocol guaranteed that putative signaling intermediates were only tested in ABAresponsive cells. Among the tested substances, InsP 3 (Fig. 3C), inositol hexakisphosphate, and nicotinic acid adenine dinucleotide phosphate (38) did not evoke anion current transients (n ϭ 6 for each compound).…”

Section: Aba Activates Anion Channels Without Rise In Cytosolic Camentioning

confidence: 99%

“…Stomatal closure represents the fastest ABA response known so far, characterized by a half-time of Ϸ5 min, and presumably does not involve gene activation. Fast stomatal closure is accomplished by the release of potassium and chloride via voltage-dependent ion channels and by metabolic degradation of the major organic anion malate (3,4).…”

mentioning

confidence: 99%

Cytosolic abscisic acid activates guard cell anion channels without preceding Ca ²⁺ signals

Levchenko

Konrad²,

Dietrich³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

163

171

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The phytohormone abscisic acid (ABA) reports on the water status of the plant and induces stomatal closure. Guard cell anion channels play a central role in this response, because they mediate anion efflux, and in turn, cause a depolarization-induced K ؉ release. We recorded early steps in ABA signaling, introducing multibarreled microelectrodes in guard cells of intact plants. Upon external ABA treatment, anion channels transiently activated after a lag phase of Ϸ2 min. As expected for a cytosolic ABA receptor, iontophoretic ABA loading into the cytoplasm initiated a rise in anion current without delay. These ABA responses could be elicited repetitively at resting and at largely depolarized potentials (e.g., 0 mV), ruling out signal transduction by means of hyperpolarizationactivated calcium channels. Likewise, ABA stimulation did not induce a rise in the cytosolic free-calcium concentration. However, the presence of Ϸ100 nM background Ca 2؉ was required for anion channel function, because the action of ABA on anion channels was repressed after loading of the Ca 2؉ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N ,N -tetraacetate. The chain of events appears very direct, because none of the tested putative ABA-signaling intermediates (inositol 1,4,5 trisphosphate, inositol hexakisphosphate, nicotinic acid adenine dinucleotide phosphate, and cyclic ADP-ribose), could mimic ABA as anion channel activator. In patchclamp experiments, cytosolic ABA also evoked anion current transients carried by R-and S-type anion channels. The response was dose-dependent with half-maximum activation at 2.6 M ABA. Our studies point to an ABA pathway initiated by ABA binding to a cytosolic receptor that within seconds activates anion channels, and in turn, leads to depolarization of the plasma membrane. stomatal closure T he plant hormone abscisic acid (ABA) provides a developmental signal serving as a chemical switch between, for instance, dormancy and growth of seeds and buds (1). Furthermore, this sesquiterpene is involved in the transmission of environmental changes like drought, saline, and cold periods into stress-adaptation processes (2). Based on the time scale of the individual ABA responses, they can be subdivided into fast (seconds up to minutes) and slow (hours up to days, or even months) signaling processes. Stomatal closure represents the fastest ABA response known so far, characterized by a half-time of Ϸ5 min, and presumably does not involve gene activation. Fast stomatal closure is accomplished by the release of potassium and chloride via voltage-dependent ion channels and by metabolic degradation of the major organic anion malate (3, 4).In search for ABA signaling intermediates, guard cells have been challenged with well characterized modulators operating in signal transduction pathways of animal cells (5-8). To a large extent, the respective substances were injected into guard cells of excised epidermal peels, and the corresponding responses were monitored (9-12). After microinjection, photolysis of caged inositol 1,4,...

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Exploring Biophysical and Biochemical Components of the Osmotic Motor that Drives Stomatal Movement*

Cited by 92 publications

References 49 publications

Rubisco Activity in Guard Cells Compared with the Solute Requirement for Stomatal Opening

Rubisco Activity in Guard Cells Compared with the Solute Requirement for Stomatal Opening

Two Voltage-Gated, Calcium Release Channels Coreside in the Vacuolar Membrane of Broad Bean Guard Cells

Cytosolic abscisic acid activates guard cell anion channels without preceding Ca ²⁺ signals

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Exploring Biophysical and Biochemical Components of the Osmotic Motor that Drives Stomatal Movement*

Cited by 92 publications

References 49 publications

Rubisco Activity in Guard Cells Compared with the Solute Requirement for Stomatal Opening

Rubisco Activity in Guard Cells Compared with the Solute Requirement for Stomatal Opening

Two Voltage-Gated, Calcium Release Channels Coreside in the Vacuolar Membrane of Broad Bean Guard Cells

Cytosolic abscisic acid activates guard cell anion channels without preceding Ca 2+ signals

Contact Info

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Cytosolic abscisic acid activates guard cell anion channels without preceding Ca ²⁺ signals