ABA Regulation of Stomatal Movement - Abscisic Acid: Metabolism, Transport and Signaling - page 297

the activated kinases activate SLAC1 by phosphorylation and trigger the efflux of
anion through SLAC1 and other anion channels; forth, the efflux of anion causes
a depolarization of the plasma membrane of guard cells, and the depolarization of
plasma membrane activates outward K + channel GORK; finally, guard cells loss
salt and water, and stomata can close. This relative complete ABA signaling path-
way is so exciting, because it is the first time that we can see an uninterrupted
ABA signaling pathway and understand much better than ever how ABA closes
stomata. However, we also should be aware that many other components involving
in the stomatal closure induced by ABA and stomatal opening inhibited by ABA
have not been integrated into the ABA signaling network yet, including the known
components as we describe above, some others components not mentioned in
this chapter, as well as the unknown components such as plasma membrane Ca 2 +
channels that will probably be identified in the future. Moreover, it was known
for many years that ABA also regulates stomatal movement in transcription level
in guard cells. The application of ABA can up- and down-regulate the expression
levels of some genes in Arabidopsis guard cells and may consequently regulate
stomatal movement. Much more work will be needed to draw the complete picture
of ABA signaling network for stomatal movement.
On the other hand, stomatal closure and opening are regulated by diverse sig-
nals, including ABA, ozone, CO 2 , ROS, and changes of air humidity and pathogen.
ABA is only one of the stimuli. Emerging results already showed that the cross talks
between ABA and other signaling are complicated; they share some key components
and also have their own specific components. For example, the mutations of GCA2
and SLAC1 impair the stomatal closure induced by ABA, ozone, ROS, CO 2 , and
changes of air humidity, but the mutation of HT1 only impairs CO 2 -induced stomata
movement without affecting ABA signaling as we mentioned above. To understand
how guard cells integrate different regulating signals together will need us to unravel
drought/ABA signaling network as well as the signaling networks of other stimuli,
and the research progress in one signaling network may unexpectively help us to
understand other signaling network for stomatal movement regulation.
Acknowledgments This work was supported by Hundred Talents Program of Chinese
Academy of Sciences (2010OHTP06) and the National Basic Research Program of China (973
program; grant No. 2012CB114300). The author apologizes to colleagues whose publications
were not cited and discussed in this chapter because of space limitation.
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