Agriculture Reference
In-Depth Information
9.1
Introduction
Nitric oxide (NO) is an endogenous molecule responsible for controlling important
physiological processes, such as control of blood pressure, immune responses,
antioxidant activities, inhibition of platelet adhesion, promotion of wound healing,
and neurotransmission, among others (Ignarro
2000
; Seabra et al.
2004
,
2007
,
2008
,
2010
; Amadeu et al.
2007
,
2008
; Simpl´cio et al.
2010
). Besides humans and
animals, NO is also an important signaling molecule in plants (Wendehenne and
Hancock
2011
). The actual role of NO in plants is mainly as a key regulator of
cellular functions, similar to those observed in animals (Beligni and Lamattina
2000
; Besson-Bard et al.
2008
; Ferreira and Cataneo
2010
). NO is a chemical
messenger in plant biology and an important regulator of many physiological
events, mainly in response to biotic and abiotic stress (Shi et al.
2012
). Physio-
logical processes such as pollen tube growth and senescence, induction of leaf cell
death, wounding, root growth, seed germination, cell expansion, stomata closure,
biotic and abiotic stresses were demonstrated to be depended to NO (Siddiqui
et al.
2011
; Baudouin
2011
; Gupta et al.
2011c
; Lin et al.
2011
,
2012
; Corpas
et al.
2011
). NO in plants is produced by hydroxylamine-mediated NO production
and also by enzymes such as plasma membrane-bound nitrite reductase, cytosolic
nitrate reductase, xanthine oxidoreductase, and nitric oxide synthase-like enzyme
(Gupta et al.
2011a
,
b
).
As discussed previously, the generation of NO has been extensively discussed;
however, NO generation from polyamines, hydroxylamine, and especially arginine
is still not fully elucidated, probably due to the lack of identification of appropriate
genes, mutants, or proteins. Gene NIA1 (nitrate reductase [NADH]) has shown to
be the most abundant source of NO, despite some functional redundancy with NIA2
(nitrate reductase 2; nitrate reductase (NADH)/nitrate reductase). Even when NIA2
is still functional, the
nia1
mutant exhibits reduced NO production. Probably in the
other possible mechanisms, difficulties with lethality, functional redundancy or
their activation under normoxia and hypoxia, could be an explanation for the fact
that no generation mutants have been isolated so far (Mur et al.
2013
).
Differently from biomedical applications, the utilization of NO donors in agri-
culture is a relatively new approach. Agricultural applications of these NO donors
(e.g., small molecular weight NO donors), such as sodium nitroprusside (SNP) and
S
-nitrosothiols (RSNOs), have been used for improving plant defense and growth
(Ederli et al.
2009
; Seabra et al.
2013
; Shi et al.
2014
). In the case of the rice
catalase mutant
nitric oxide excess 1
(
noe1
), higher levels of H
2
O
2
induced the
generation of NO, suggesting that NO acts as an important endogenous mediator in
H
2
O
2
-induced leaf cell death and generation of reactive nitrogen species (RNS).
Studies showed that RNS and reactive oxygen species (ROS) are important partners
in plant leaf cell death. A recent review reported the progress on H
2
O
2
-induced leaf
cell death and the interference of RNS and ROS signals in the plant hypersensitive
response (HR), leaf senescence, and leaf cell death triggered by diverse environ-
mental conditions (Wang et al.
2013
).
