Agriculture Reference
In-Depth Information
A large number of herbicides are widely used in agriculture. Some experimental
evidences exist on the relationship of PAs and herbicides such as paraquat, an inten-
sively used oxidative stress inducer (Groppa and Benavides
2008
). In
Arabidopsis,
treated with paraquat, there was an increase in put, but not spd and spm (Benavides
et al.
2000
). Exogenous addition of PAs was effective in protection against paraquat
toxicity to various degrees in
Arabidopsis
(Benavides et al.
2000
) and in maize
leaves (Durmus and Kadioglu
2005
). These results suggested that PAs protective
function may be due to the antioxidative function.
Taken together, PAs are growth regulators present in plants implicated in vast
number of physiological processes in growth and development and abiotic and bi-
otic stress responses (reviewed in Bouchereau et al.
1999
; Groppa and Benavides
2008
; Alcázar et al.
2010a
; Wimalasekara et al.
2011a
). As discussed in this review,
differential regulation of PA biosynthesis and catabolism play important roles in
responding to several types of abiotic stresses leading to stress tolerance. Availabil-
ity of information about key genes in biosynthetic and catabolic pathways provide
useful information in manipulating the same for the production of gain and loss of
function mutants which in turn provide the underlying molecular mechanism of PA
functions. For example, overexpression of PA biosynthetic genes,
ADC1
and
ADC2
was successful in generating several plant species ranging from the model plant
Arabidopsis
to the important crop plant rice that exhibited enhanced tolerance to a
variety of stresses. Further, transgenic plants (
Arabidopsis,
rice, pear) overexpress-
ing spd and spm synthase genes
SPDS
and
SPMS
showed enhanced tolerance to a
number of abiotic stresses (Groppa and Benavides
2008
; Alcázar et al.
2010a
). In
most of the cases, these transgenic plants showed tolerance to a broad spectrum of
abiotic stresses suggesting interaction in mechanisms of stress resistance common
in different stress types.
Importance of PA catabolic enzymes CuAO/DAO and PAO in plant development
and stress tolerance is extensively reviewed (Cona et al.
2006
; Kusano et al.
2008
;
Moschou et al.
2008b
; Angelini et al.
2010
; Wimalasekara et al.
2011a
). For ex-
ample, overexpression of
CuAO
in tobacco showed enhanced tolerance to salt stress
(Moschou et al.
2008b
) and overexpression of ZmPAO in tobacco showed enhanced
wound-healing response (Angelini et al.
2008
). Most of the PA catabolic functions
are associated with H
2
O
2
that is produced by the activity of CuAO/DAO and PAO.
In most of the instances, H
2
O
2
produced in this manner is involved in reactions
occurring during stress-induced cell wall modifications, in PCD, and as a second
messenger in signalling stomatal regulation. Several experimental evidences exist
regarding the roles of CuAO/DAO and POA in biotic stress tolerance especially in
triggering the hypersensitive response and CPD (reviewed in Walter
2003
; Angelini
et al.
2010
; Moschou et al.
2008a
). Transfer of the knowledge obtained from rather
limited plant species over to valuable crop species will be a future challenge in the
agriculture industry despite the many constrains that exist.
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