Agriculture Reference
In-Depth Information
and Zambryski
1995
; Solecka
1997
). The role of phenolic derivatives has been dis-
cussed frequently in the studies related to defense strategies of plants (Kurkin
2003
;
Bednarek et al.
2005
; Mandal et al.
2010
). Among other things, SA has crucially
been discovered in up-regulating the cellular H
2
O
2
content and other reactive spe-
cies, and thus, the induction of hypersensitive response (HR). The level of ROS has
extensively been shown to attenuate plant growth physiology at the cost of plant
growth and productivity.
An intermediate stage between two extremes of host and invader point of view
could be assumed, where forced modulation of host cell metabolism is not as strong
to completely overpower its defense response (based on aforementioned triple fac-
tors, i.e., abiotic, host and invaders'). Differential push of two during the daily cycle
of environment allows the partial resistance/virulence with conditional ingression
of invader restricting the growth of intruder within the limits of threshold dam-
age (Berger et al.
2007
; Anderson et al.
2010
). During the evolution of this semi-
compatible system, partial utilization of host metabolites and metabolization of
microbial secretions (sometimes toxic products) or cross resistance to abiotic/biotic
factors may pave the way to facultative symbiotic relation. After a long gap of
growth adjustment, plant system may incorporate these invaders as part of their life
cycle at the specific stage of growth or even as a full-fledged integral organelle.
Activation of phenolic compounds under different abiotic stresses and biotic
challenges has been reported in several studies (Rivero et al.
2001
). It is presumed
that the phenolic compounds play a crucial role in signal transduction and defense
response under biotic (Holuigue et al.
2007
; Malamy et al.
1990
; Durner et al.
1997
)
and abiotic stresses (Dixon and Paiva
1995
; Solecka
1997
; Helle et al.
1998
). SA
plays a crucial role, modulating the cellular redox homeostasis in different plant
microbe interactive systems, particularly associated with the onset of defense re-
sponses up to diversion of stress signaling, executing programmed cell death (PCD;
Gut-Rella et al.
1994
; Alvarez
2000
; Greenberg et al.
2000
). Their signaling has
recently been implicated in interplant priming of defense responses through mobile
signals that travel as volatile intermediates of SA and JA (Heil and Ton
2008
). Thus,
phenols, particularly SA, regulate plant metabolism under different overlapping en-
vironmental and indigenous cues (Fig.
6.1
).
3 Activated SA Biosynthesis, Metabolism and Mobilization
The production of H
2
O
2
with the interplay of SA and ROS in the local defense
reaction is believed to positively feedback the activated biosynthesis of SA via
phenylpropanoid pathway (Catinot et al.
2008
; Lee et al.
1995
; Durner and Klessig
1996
; Kawano
2003
). Earlier, two routes of biosynthesis of SA from shikimate-
derived phenylalanine had been suggested. Phenylalanine is converted to cinnamic
acid by phenyl ammonia lyase (PAL), which forms SA either through benzoic acid
hydroxylation or through O-coumaric acid de-carboxilation. The benzoic acid and
O-coumaric acid may be formed either by the de-carboxilation or 2-hydroxilation
