A transient outward-rectifying K ⁺ channel current down-regulated by cytosolic Ca ²⁺ in Arabidopsis thaliana guard cells

Abstract

A BSTR ACTSustained (noninactivating) outwardrectifying K ؉ channel currents have been identified in a variety of plant cell types and species. Here, in Arabidopsis thaliana guard cells, in addition to these sustained K ؉ currents, an inactivating outward-rectifying K ؉ current was characterized (plant A-type current: I AP ). I AP activated rapidly with a time constant of 165 ms and inactivated slowly with a time constant of 7.2 sec at ؉40 mV. I AP was enhanced by increasing the duration (from 0 to 20 sec) and degree (from ؉20 to ؊100 mV) of prepulse hyperpolarization. Ionic substitution and relaxation (tail) current recordings showed that outward I AP was mainly carried by K ؉ ions. In contrast to the sustained outward-rectifying K ؉ currents, cytosolic alkaline pH was found to inhibit I AP and extracellular K ؉ was required for I AP activity. Furthermore, increasing cytosolic free Ca 2؉ in the physiological range strongly inhibited I AP activity with a half inhibitory concentration of Ϸ 94 nM. We present a detailed characterization of an inactivating K ؉ current in a higher plant cell. Regulation of I AP by diverse factors including membrane potential, cytosolic Ca 2؉ and pH, and extracellular K ؉ and Ca 2؉ implies that the inactivating I AP described here may have important functions during transient depolarizations found in guard cells, and in integrated signal transduction processes during stomatal movements.

Aluminium triggers malate-independent potassium release via ion channels from the root apex in wheat

“…In fact, recent studies have verified that cytosolic acidification can certainly inactivate outward-rectifying K + channels in Arabidopsis guard cells (Roelfsema and Prins 1998) or root cells (Lacombe et al 2000) and an outward K + current in mesophyll cells of maize (Keunecke and Hansen 2000), However, the effect of the cytosolic alkalization on the activation of outward K + channels still remains a controversial subject. In contrast to the previous reports, a transient outward K + current in guard cells is strongly decreased by intracellular alkalization (Pei et al 1998), and an outward-rectifying K + channel (GORK) of guard cells is insensitive to the alkalization of medium pH (Ache et al 2000). At present, we cannot conclude whether cytosolic alkalization further stimulates Al-independent K + efflux.…”

Plant calcium signaling and monitoring: pros and cons and recent experimental approaches

“…1) and other cellular parameters which in turn mediate biochemical and physiological responses of the plant. It has been shown that [Ca:+]c is involved in ion channel activity (Pei et al 1998, Czempinski etal. 1997, Allen etal.…”

Control of Guard Cell Ion Channels by Hydrogen Peroxide and Abscisic Acid Indicates Their Action through Alternate Signaling Pathways

“…At first sight, it is surprising that H 2 O 2 should suppress I K,out because H 2 O 2 induces stomatal closure in epidermal strips of Arabidopsis and V. faba (Pei et al, 2000;Zhang et al, 2001b) and, therefore, might be expected to stimulate K ϩ loss from the cells. However, other pathways for K ϩ efflux have been reported (Thiel et al, 1992;Pei et al, 1998) and their response to H 2 O 2 is unknown (see also Duprat et al, 1995).…”