Agriculture Reference
In-Depth Information
the anion channel-associated1 (SLAC1). Protein phosphatases that function
in ABA-related stomatal movement can be regulated by ROS, and ABI1 and
ABI2 activities are significantly inactivated by H
2
O
2
(Meinhard and Grill
2001
; Meinhard et al.
2002
). Recent research showed that the GSH-deficient
Arabidopsis
mutant
cad2
-
1
showed enhanced H
2
O
2
-induced stomatal closure
and a significant increase of ROS accumulation in whole leaves in response
to ABA. The
cad2
-
1
mutant enhanced the activation of Ca
2
+
-permeable chan-
nels by H
2
O
2
, but did not affect the ABA regulation of S-type anion channels
(Munemasa et al.
2013
).
ROS also regulate the ABA response of guard cells through MAPK cascades.
Time-course analysis showed that the accumulation of H
2
O
2
activates MAPK
activity, which promotes stomatal closure (Desikan et al.
2004
; Jiang et al.
2008
). Double-mutant
mpk9
/
12
showed increased transpirational water loss and
decreased sensitivity in terms of the stomatal response to ABA and H
2
O
2
, when
compared with wild-type plants. Both ABA and H
2
O
2
can enhance the pro-
tein kinase activity of MPK12. These results suggested that these two MPK act
upstream of anion channels and downstream of ROS to promote ABA signalling in
guard cells (Jammes et al.
2009
).
The
siz1
mutant, which impairs the SIZ-type small ubiquitin-related modifier
E3 ligase in
Arabidopsis
(Muraoka and Miura
2005
), displayed ABA hypersen-
sitivity (Miura and Hasegawa
2009
). SIZ1 negatively affects stomatal closure
and drought tolerance through the accumulation of SA (Miura et al.
2013
).
Endogenous ABA is not involved in SA-induced stomatal closure because SA
can induce stomatal closure not only in
Arabidopsis
wild-type plants but also in
ABA-deficient
aba2
mutants (Issak et al.
2013
). Moreover, SA-induced stomatal
closure is accompanied by the production of ROS (Issak et al.
2013
). Together,
all of these results suggest that, although the ABA and SA signalling pathways
are independent of each other, the two regulators coordinately regulate ROS
production in response to drought and pathogen invasion. Detailed informa-
tion for crosstalk between SA and ABA signalling in guard cells have yet to be
established.
10.4.2 Dormancy and Germination of Seed
ABA is a key regulator of seed dormancy and germination. A recent study found
that blue light inhibits the germination of barley by induction of the expression
of the ABA biosynthetic gene that encodes 9-cis-epoxycarotenoid dioxygenase
(NCED) and dampening of expression of the ABA-degradation gene, 8′-hydrox-
ylase, which increases ABA content in the grain and prevents the completion of
germination (Jose et al.
2014
). Considerable research has explored the interac-
tion of ABA with ROS in seed dormancy and germination. ROS have recently
emerged as key players in seed physiology (Bailly et al.
2008
). There are sev-
eral reasons why the mechanisms by which ROS act as signalling molecules in
Search WWH ::
Custom Search