Biology Reference
In-Depth Information
Catalase
PAMP signals
H
2
O
2
H
2
O
2
degradation
Benzoic acid accumulation
Release of
molecular oxygen
Salicylic acid
Fig. 5.4
ROS-mediated salicylic acid biosynthesis
(Vandenabeele et al.
2003
). SA is known to bind catalase (Chen et al.
1993
; Conrath
et al.
1995
). This binding inhibits the activity of the enzyme in vitro, and hence it is
suggested that the inactivation of catalase by SA may increase the levels of H
2
O
2
(León et al.
1995
; Torres et al.
2006
). Several effector proteins involved in SA-induced
defense responses have been identifi ed. The fi rst protein identifi ed as a salicylic acid-
binding protein is the cytosolic (peroxisomal) tobacco catalase (CAT) that reversibly
binds SA (Chen et al.
1993
; Conrath et al.
1995
). SA inhibits CAT's H
2
O
2
-degrading
activity (Durner and Klessig,
1996
; Wendehenne et al.
1998
). SA-mediated inhibi-
tion of CAT may generate H
2
O
2
, which may activate the ROS signaling system
inducing expression of defense genes (Chen et al.
1993
). ROS signaling system may
act both in upstream and downstream of SA signaling (Slaymaker et al.
2002
).
Thus H
2
O
2
may increase accumulation of SA and SA may increase accumulation
of H
2
O
2
. ROS metabolism can affect the function of NPR1 by controlling NPR1
redox state (Mou et al.
2003
). NPR1 is an important regulator of responses down-
stream of SA (Mou et al.
2003
; Zhang et al.
2003
). It has also been demonstrated
that calcium-dependent generation of ROS subsequently induces the production of
salicylic acid and PR genes expression (Chen et al.
2011
).
5.11
Interplay Between ROS and Ethylene Signaling
Systems
ROS may function in ethylene signaling system. An increase in H
2
O
2
was able to
trigger transcriptional changes of genes involved in the biosynthesis of ethylene.
S-adenosyl-L-methionine synthetase is the fi rst enzyme in the ethylene biosynthesis
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