Changes in cytosolic pH and calcium of guard cells precede stomatal movements.

Abstract

Stomatal opening is induced by indoleacetic acid (IAA), cytokinins, and fusicoccin (FC), whereas stomatal closure is induced by abscisic acid (ABA). To test the effect of thes growth regulators on guard cell cytoslic Ca2+ ([Ca2+]k,) and pH (pHc.), epidermal strips were taken from the lower side of leaves of the orchid Paphiopedilum tonsum and were loaded with acetomethoxy-esterified forms ofthe Ca2+ indicator fluo-3 or the pH indicator 2',7'-bis(2-carboxyethyl)-5 (6) The opening and closure of stomatal pores, which regulate gas exchange in leaves, are associated with large changes in K+ levels in the guard cells (1). The K+ content of the guard cells is increased during stomatal opening (1), which is induced by light (2), low CO2 levels (3), humidity (4), indoleacetic acid (IAA) (5), fusicoccin (FC) (6), and cytokinins (7). Stomatal closure is associated with K+ release from the vacuoles and efflux across the plasma membrane (1), and closure can be induced by elevated levels of CO2 (2, 3), darkness (2), decreased humidity (2, 4), and abscisic acid (ABA) (8). It 1790The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Roles of Higher Plant K+ Channels

“…These cellular regulation mechanisms of guard cell K' channels and their physiological implications for stomatal movements are reviewed in more detail elsewhere (Assmann, 1993;Ward et al, 1995), but examples are: (a) ABAinduced Ca2+ elevation and the inhibition of stomatal opening by Ca2+, which correlates with a down-regulation of K+i, channels by elevated Ca2+ concentrations (Schroeder and Hagiwara, 1989); (b) enhancement of K+,,, channel activity by cytosolic alkalinization can be triggered by ABA-induced alkalinization (Irving et al, 1992;Blatt and Armstrong, 1993); and (c) the activity of Kfi, channels is increased by extracellular acidification, which can provide an additional mechanism, enhancing proton pumpinduced stomatal opening (Blatt, 1992).…”

“…VK channels can conduct large K+ fluxes from guard cell vacuoles to the cytosol and have been proposed to provide a pathway for vacuolar, Ca*+-dependent K+ release during stomatal closing. In this model, vacuolar Ht ATPases would hyperpolarize the tonoplast to drive channel-mediated vacuolar K+ release ) and simultaneously contribute to the cytosolic alkalinization that occurs in response to ABA during stomatal closing (Irving et al, 1992;Blatt and Armstrong, 1993).…”

Sphingosine-1-phosphate (S1P) mediates darkness-induced stomatal closure through raising cytosol pH and hydrogen peroxide (H2O2) levels in guard cells in Vicia faba

“…The changes in cytosolic pH were monitored with BCECF-AM, as described earlier by Irving et al [28] with minor modifications.…”

“…Cytosolic alkalization in guard cells is a common phenomenon in ABA-and MJ-induced stomatal closure in A. thaliana, Pisum sativum, and Paphiopedilum tonsum [27][28][29][30]. ABA elevates the level of cytosolic free Ca 2+ ([Ca 2+ ] cyt ) in accordance with cytosolic alkalization in Paphiopedilum tonsum guard cells [28]. Cytosolic alkalization and cytosolic Ca 2+ oscillation coordinately function in ABA and MJ signaling in A. thaliana guard cells [31].…”

“…Cytosolic alkalization also activates outward K + currents and inactivates inward K + currents to promote a net efflux of K + in Vicia faba guard cells [32]. In addition, cytosolic acidification in guard cells has been shown to mediate stomatal opening by kinetin (KT), indole-3-acetic acid (IAA), and fusicoccin (FC) [28] and to activate inward K + currents [33]. These results suggest that changes in cytosol pH are closely involved in modulating stomatal movement.…”