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Ca
2+
influx
Calcium signature
NADPH oxidase
H
2
O
2
Lipoxygenase
Jasmonate biosynthesis
Fig. 4.12
Ca
2+
infl ux/ROS/lipoxygenase-mediated jasmonate biosynthesis
4.21.6
Ethylene Signaling System
Ethylene production is an important downstream event in Ca
2+
signaling system.
Ca
2+
infl ux through Ca
2+
channels results in Ca
2+
waves (calcium signature) in
cytosol. The calcium waves-activated calcium-dependent protein kinase (CDPK)
activates 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, the key enzyme
involved in biosynthesis of ACC, a precursor for biosynthesis of ethylene (Sebastiá
et al.
2004
). The Ca
2+
infl ux is involved in activation of ACC oxidase, which is a key
enzyme in biosynthesis of ethylene (Fig.
4.13
; Gallardo et al.
1999
). ACC oxidase
activities as well as ethylene production from chickpea seeds were strongly inhib-
ited by EGTA (ethylene glycol-bis (
-tetraacetic
acid), a selective extracellular calcium ion chelator, indicating that the infl ux of Ca
2+
is important for the ACC oxidase activity. The EGTA inhibition was restored by
exogenous calcium ion treatment. Treatment of embryonic axes with either vera-
pamil or LaCl3 (both Ca
2+
channel blockers) or TMB8 (an intracellular Ca
2+
antago-
nist) provoked an inhibition of both ACC oxidase activity and ethylene production
(Gallardo et al.
1999
). These results suggest the involvement of calcium ion fl uxes
and intracellular calcium levels in the activity of the last step of the ethylene biosyn-
thetic pathway.
C a
2+
infl ux may play an important role in ethylene signaling system (Raz and
Fluhr
1992
; Kwak and Lee
1997
; Gallardo et al.
1999
; Reddy et al.
2000
). Blocking
of Ca
2+
fl uxes inhibits ethylene-induced gene expression and artifi cial elevation of
[Ca
2+
]
cyt
induces the expression of ethylene regulated genes in the absence of ethyl-
ene (Kwak and Lee
1997
; Gallardo et al.
1999
). Expression of several ethylene-
inducible defense genes was found to be modulated by Ca
2+
. The induction of acidic
γβ
-aminoethyl ether) N,N,N
′
,N
′
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