Differential abscisic acid regulation of guard cell slow anion channels in Arabidopsis wild-type and abi1 and abi2 mutants.

Abstract

Abscisic acid (ABA) regulates vital physiological responses, and a number of events in the ABA signaling cascade remain t o be identified. To allow quantitative analysis of genetic signaling mutants, patch-clamp experiments were developed and performed with the previously inaccessible Arabidopsis guard cells from the wild type and ABA-insensitive (abi) mutants. Slow anion channels have been proposed t o play a rate-limiting role in ABA-induced stomatal closing. We now directly demonstrate that ABA strongly activates slow anion channels in wild-type guard cells. Furthermore, ABA-induced anion channel activation and stomatal closing were suppressed by protein phosphatase inhibitors. In abil-7 and abi2-7 mutant guard cells, ABA activation of slow anion channels and ABA-induced stomatal closing were abolished. These impairments in ABA signaling were partially rescued by kinase inhibitors in abil but not in abi2 guard cells. These data provide cell biological evidence that the abi2 locus disrupts early ABA signaling, that abil and abi2 affect ABA signaling at different steps in the cascade, and that protein kinases act as negative regulators of ABA signaling in Arabidopsis. New models for ABA signaling pathways and roles for abil, abi2, and protein kinases and phosphatases are discussed.

Nonselective Block by La 3+ of Arabidopsis Ion Channels Involved in Signal Transduction

“…The significance of anion channel inhibition by La 3+ is realized when one considers the large number of signaling pathways that include anion channel activation as a step (Schroeder & Hagiwara, 1989;Elzenga et al, 1995;Schmidt et al, 1995;Cho & Spalding, 1996;Pei et al, 1997). The effective block of anion channels by La 3+ (Fig.…”

“…Concern over using La 3+ arises if this result holds true in vascular plants, where it is now appreciated that the activation of anion channels is key to many diverse signal transduction pathways (Ward, Pei & Schroeder, 1995). For example, abscisic acid activates anion channels in guard cells to induce stomatal closure (Pei et al, 1997), auxin alters the voltage dependence of an anion channel in guard cells and opens stomata (Marten, Loshe & Hedrich, 1991), and blue light activates an anion channel in Arabidopsis hypocotyl cells to inhibit their growth (Cho & Spalding, 1996) and induce anthocyanin accumulation (Noh & Spalding, 1998). With various types of ion channels participating in such diverse signaling pathways, it is crucial to fully understand the specificity of the pharmacological agents used to dissect these pathways.…”

Activated expression of AtWRKY53 negatively regulates drought tolerance by mediating stomatal movement

“…We next investigated the sensitivity of the guard cells to ABA, using epidermal peels of 53OV lines and Col-0 incubated in a buffer solution under strong light conditions for 3 h to fully open the stomata. The peels were then treated with 5 lM ABA for 2 h (Pei et al 1997). The ratio of stomatal length to width was calculated to determine the degree of stomatal closure.…”

“…Stomatal closure assays were conducted as described previously (Pei et al 1997). Rosette leaves were floated in a solution containing 50 lM CaCl 2 , 10 mM KCl, 10 mM MES (2-(N-morpholino)ethanesulfonic acid)-Tris, pH 6.15, and exposed to light for 2 h. Subsequently, ABA was added to the solution up to 5 lM.…”

Plant Environmental Stress Responses for Survival and Biomass Enhancement

“…Membrane depolarization also activates outward K þ channels, such as GORK (gated outwardly rectifying K þ channel), thereby resulting in K þ efflux from guard cells. The anions and K þ effluxes from guard cells lead to a loss of guard cell turgor, followed by stomatal closure [22][23][24][25]. H þ -ATPase has a proton efflux activity, which is induced by blue light and low CO 2 concentrations.…”