Agriculture Reference
In-Depth Information
15.1 Introduction
Stomata locate mainly in the surface of plant leaves, and a stomata pore is sur-
rounded by two guard cells. Stomatal movement, including stomatal opening and
closure, is driven by the changes of volume and osmotic turgor pressure in the two
guard cells. Stomatal opening results from the accumulation of inorganic ions,
including K
+
, Cl
−
, NO
3
−
, and osmotic organic molecules such as malate, which
is mainly from the hydrolyzing of sugar and starch. Stomatal closure is driven by
the release of the inorganic ions from guard cells plus the gluconeogenic conver-
sion of malate into osmotic inactive starch. Multiple abiotic and biotic stimuli can
regulate the stomatal movement. When sun rises at morning, light induces stomatal
opening, and plants intake CO
2
for photosynthesis, loss water by transpiration, and
release oxygen into atmosphere through stomatal pores. During night time, dark-
ness induces stomatal closure. Further research found that both blue light and red
light can induce stomatal opening. Blue light induces stomatal opening by activat-
ing plasma membrane H
+
-ATPase, which pumps H
+
out of guard cells to hyper-
polarize the plasma membrane (Kasahara et al.
2002
; Briggs and Christie
2002
),
and consequently activate plasma membrane inward-rectifying K
+
channels (K
in
).
The identification of OST2 (open stomata 2), a H
+
-ATPase in
Arabidopsis
, pro-
vides genetic evidences showing the functions of H
+
-ATPase in stomatal opening.
ost2
mutants show a constitutive activity of H
+
-ATPase, which consequently leads
to open stomata and an insensitivity to ABA-induced stomatal closure (Merlot et al.
2007
). Therefore, OST2 is also named as AHA1 (
Arabidopsis
H
+
ATPase). Red
light is not only a signal, but also an energy source for mesophyll and guard cells.
Red light can induce stomatal opening by reducing CO
2
concentration in guard cell
(Shimazaki et al.
2007
). Stomatal movement can be regulated by changes of atmos-
phere CO
2
level. Elevated CO
2
induces stomatal closure, and low CO
2
induces sto-
matal opening to ensure an efficient CO
2
uptake for photosynthesis in a variable
environmental CO
2
level. Ozone can enter plants through stomata pores, and ozone
and reactive oxygen species (ROS) derived from ozone can damage plant cells.
Stomata are capable to be closed in response to ozone to protect plants from the
damage. The changes of relative air humidity can regulate stomatal movement as
well, the decreases of relative air humidity close stomata, and the increases of rela-
tive air humidity can open stomata. Besides environmental stimuli, phytohormone,
including ABA, cytokinin, auxin, ethylene, and jasmonates, can all have regulatory
effects on stomatal movement, especially ABA, which is the most specific natu-
ral hormone than any others to induce stomatal closure to prevent water loss and
protect plants from environmental harmful invasion. ABA-induced stomatal clo-
sure is the most well-studied signaling mechanism, but it is also well known that
some key components of ABA signaling pathway in stomata play essential roles in
other stimuli-induced stomatal movement, such as SLAC1 and GCA2. The muta-
tions of SLAC1 and GCA2 impair ABA-, light-, and high CO
2
-induced stomatal
closure (Negi et al.
2008
; Vahisalu et al.
2008
). On the contrary, the disruption of
HT1 (high leaf temperature 1),
ʲ
-carbonic anhydrases
ʲ
-CA1 and
ʲ
-CA4, and the
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