Biology Reference
In-Depth Information
5.8
Interplay Between ROS and NO Signaling Systems
H
2
O
2
production has been shown to be required for NO synthesis. NO synthesis is
severely reduced in the NADPH oxidase
Arabidopsis
double mutant
atrbohD
atrbohF
, suggesting that endogenous H
2
O
2
production is required for NO synthesis
(Bright et al.
2006
). Nitric oxide is often produced at the same time and in the same
locations in plants as ROS (Neill et al.
2003
). NO may also react with thiol groups on
proteins in a process known as S-nitrosylation, to produce a -S-NO group (Hancock
et al.
2006
). NO is known to modify the same type of proteins which are modifi ed by
H
2
O
2
(Lindermayr et al.
2005
). These results suggest that there may be a competition
between H
2
O
2
and NO at the level of thiol modifi cation which may determine the
exact signaling processes that ensue (Hancock et al.
2006
). It has also been reported
that ROS activates the mitogen-activated protein kinase MPK6. The ROS-activated
MAPK modulates nitric oxide biosynthesis in
Arabidopsis
(Wang et al.
2010
).
5.9
Interplay Between ROS and MAPK Signaling Systems
H
2
O
2
activates MAP kinases that modulate gene expression and transduce cellular
responses to extracellular stimuli (Desikan et al.
1999
; Kovtun et al.
2000
; Samuel
et al.
2000
; Pitzschke and Hirt
2006
,
2009
; Pitzschke et al.
2009a
,
b
). Activation of
MAP kinases by ROS has been reported in
Arabidopsis
(Grant et al.
2000a
; Kovtun
et al.
2000
; Desikan et al.
2001
), tobacco (Samuel and Ellis
2002
), and maize
(Zhang et al.
2006
). The MAPKKKs ANP1 and OMTK1 have been shown to be
activated by H
2
O
2
(Kovtun et al.
2000
; Nakagami et al.
2004
).
5.10
Interplay Between ROS and Salicylic Acid Signaling
Systems
H
2
O
2
stimulates salicylic acid (SA) biosynthesis in tobacco (León et al.
1995
). SA is
synthesized in tobacco leaves from benzoic acid (BA) after elicitation (Yalpani et al.
1993
). Elicitors trigger the oxidative burst, which results in production of H
2
O
2
. H
2
O
2
causes an intracellular accumulation of BA. The conversion of BA to SA is catalyzed
by benzoic acid 2-hydroxylase (BA2H), an inducible enzyme that is synthesized de
novo in response to increased BA level (León et al.
1993
). BA2H is a soluble Cyt
P-450 monoxygenase that uses molecular oxygen for the 2-hydroxylation of benzoic
acid (León et al.
1995
). The increased 2-hydroxylation activity may be due to the
additional oxygen arising from the H
2
O
2
degraded by catalase (León et al.
1995
). The
catalase-mediated release of molecular oxygen from peroxide may lead to the activa-
tion of BA2H, resulting in enhanced accumulation of SA (Fig.
5.4
; León et al.
1995
).
An UDP-glucose:SA:glucosyltransferase that converts SA to SA
-glucoside in
tobacco is up-regulated after 30 min of exposure to external stimulus and it suggests
the accumulation of SA in elicited tobacco plants at a transcriptional level
β
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