events in guard cells. Black boxes indicate the
beginning and duration of an event. ROS, reactive oxygen
species.
Early ABA signaling events in guard cells
by Pei Z. M., Kuchitsu K. (2005)
- Zhen-Ming Pei, Department of Biology, Duke University, Durham, USA
- Kazuyuki Kuchitsu,Department of Applied Biological Science, and Genome and Drug Research Center, Tokyo University of Science, Noda, Japan
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in Journal of Plant Growth Regulation 24: 296–307 – DOI: 10.1007/s00344-005-0095-x –
http://www.esalq.usp.br/lepse/imgs/conteudo_thumb/Early-ABA-Signaling-Events-in-Guard-Cells.pdf
guard cells. Abscisic acid is perceived by an unknown
receptor (AAR), which triggers [Ca2+]i increases via H2O2-
activated Ca2+ influx channels (ICa) or Ca2+ release from
internal stores. The elevated [Ca2+]i induces further H2O2
production via stimulating NADPH oxidases, leading to a
positive feedback of [Ca2+]i increases. Both S-type and Ftype
anion channels (CLC) are activated by elevated
[Ca2+]i, resulting in anion efflux and depolarization of the
membrane potential. The depolarized membrane potential
promotes K+ efflux via K+ outward channels (Kout)
and inhibits K+ influx from K+ inward channels (Kin).
Meanwhile, K+ influx via Kin is inhibited by elevated
[Ca2+]i. The efflux of cations and anions reduces the solute
concentration in guard cells, and thus leads to water
efflux and stomatal closing.
Abstract
The plant hormone abscisic acid (ABA) regulates a wide variety of plant physiological and developmental processes, particularly responses to environmental stress, such as drought.
In response to water deficiency, plants redistribute foliar ABA and/or upregulate ABA synthesis in roots, leading to roughly a 30-fold increase in ABA concentration in the apoplast of stomatal guard cells. The elevated ABA triggers a chain of events in guard cells, causing stomatal closure and thus preventing water loss.
Although the molecular nature of ABA receptor(s) remains unknown, considerable progress in the identification and characterization of its downstream signaling elements has been made by using combined physiological, biochemical, biophysical, molecular, and genetic approaches.
The measurable events associated with ABA-induced stomatal closure in guard cells include, sequentially, the production of reactive oxygen species (ROS), increases in cytosolic free Ca2+ levels ([Ca2+]i), activation of anion channels, membrane potential depolarization, cytosolic alkalinization, inhibition of K+ influx channels, and promotion of K+efflux channels.
This review provides an overview of the cellular and molecular mechanisms underlying these ABA-evoked signaling events, with particular emphasis on how ABA triggers an “electronic circuitry” involving these ionic components.
