ABA depolarizes guard cells in intact plants, through a transient activation of R‐ and S‐type anion channels

Abstract

Summary During drought, the plant hormone abscisic acid (ABA) induces rapid stomatal closure and in turn reduces transpiration. Stomatal closure is accompanied by large ion fluxes across the plasma membrane, carried by K+ and anion channels. We recorded changes in the activity of these channels induced by ABA, for guard cells of intact Vicia faba plants. Guard cells in their natural environment were impaled with double‐barrelled electrodes, and ABA was applied via the leaf surface. In 45 out of 85 cells tested, ABA triggered a transient depolarization of the plasma membrane. In these cells, the membrane potential partially recovered in the presence of ABA; however, a full recovery of the membrane potentials was only observed after removal of ABA. Repetitive ABA responses could be evoked in single cells, but the magnitude of the response varied from one hormone application to the other. The transient depolarization correlated with the activation of anion channels, which peaked 5 min after introduction of the stimulus. In guard cells with a moderate increase in plasma membrane conductance (ΔG < 5 nS), ABA predominantly activated voltage‐independent (slow (S)‐type) anion channels. During strong responses (ΔG > 5 nS), however, ABA activated voltage‐dependent (rapid (R)‐type) in addition to S‐type anion channels. We conclude that the combined activation of these two channel types leads to the transient depolarization of guard cells. The nature of this ABA response correlates with the transient extrusion of Cl− from guard cells and a rapid but confined reduction in stomatal aperture.

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

“…Guard cells in intact plants previously were found to hyperpolarize in the light, to an average membrane potential of Ϫ110 mV (21). To enable recordings of anion channel conductance at depolarized potentials, K ϩ channels can be blocked by extracellular Ba 2ϩ and intracellular Cs ϩ (24). Under these conditions (21), the average guard cell membrane potential was further hyperpolarized and fluctuated, probably due to small changes in channel activities ( Fig.…”

“…In previous studies (21,23,24), we used multibarreled microelectrodes impaled into guard cells of intact plants to record plasma membrane responses to blue and red light, CO 2 , and ABA. Here, we extended this method by injecting the Ca 2ϩ reporter dye FURA-2 to simultaneously monitor ABA-induced changes in the cytoplasmic free Ca 2ϩ concentration and anion channel activity.…”

“…Previous studies (24,39) have shown that the ABAevoked anion currents are carried by rapidly activating and inactivating (R-type), and slowly activating, noninactivating (Stype) anion channels (24, 39, 40). However, in isolated guard cell protoplasts, long-term incubation with ABA induced activation of S-type channels only (40).…”

Roles of ion channels and transporters in guard cell signal transduction

“…In the presence of extracellular anions, including malate 2À and Cl À , which would accumulate in the apoplast during stomatal closure, the voltage-regulation of guard cell R-type channels shifts to more negative voltages. This promotes anion efflux through the channels and in this manner R-type channels can also contribute to membrane depolarization [62,92]. Both R-and S-type channels are permeable to a range of anions, including those of physiological relevance to guard cell function: malate 2À , Cl À , and NO À 3 .…”

Interactions between theS-Domain Receptor Kinases and AtPUB-ARM E3 Ubiquitin Ligases Suggest a Conserved Signaling Pathway in Arabidopsis

“…Given that the plasma membrane is the predicted location of fulllength SD1 receptor kinases, it is conceivable that AtPUB9 is interacting with related SD1 receptor kinases in the BY-2 cells. This observation is quite interesting because the plasma membrane is one of the major sites of action for ABA, where ABA controls various membrane-bound transporters and ion channels regulating the closure of stomata (Finkelstein et al, 2002;Roelfsema et al, 2004). A plasma membranelocalized, putative G protein-coupled receptor has also been proposed to be an ABA receptor (X.…”