Geoscience Reference
In-Depth Information
essential role in the defence of plants against water stress, is
strongly expressed in response to JA and to other stresses such
as mannitol, NaCl and wounding in
Populus alba
×
P. tremula
var. glandulosa.
Nitric oxide
NO functioning as a signal in hormonal responses, is a gaseous-
free radical, diatomic molecule and plays important roles in
diverse physiological and pathological processes in plants cellu-
lar and developmental mechanisms. NO synthesis in plants takes
place by arginine- and nitrite-dependent pathways. Nitric oxide
synthase (NOS) catalyses the generation of NO from the input
of O
2
and NADPH. NO has dual roles in plant cell physiology.
Endogenous NO is stringently controlled in low-level homeosta-
sis through the production and elimination of NO under normal
physiological condition. Low concentrations of NO can not only
interrupt ROS-triggered chain reaction, but can also improve
plant resistance by inducing gene expression (Beligni and
Lamattina, 1999, 2000). When the cell alters itself or is exposed
to environmental stress or climate change, the rapid increase of
NO elicits an oxidative burst resulting in cell death (He et al.,
2012). Parani et al. (2004) studied the gene expression analysis
in
Arabidopsis
using microarray in response to 0.1 and 1.0 mm
sodium nitroprusside (SNP), a donor of NO. They found 342
up-regulated and 80 down-regulated genes in response to NO
treatments (Parani et al., 2004). They observed the up-regulation
of several genes encoding disease-resistant proteins, WRKY
proteins, transcription factors, zinc-finger proteins, glutathione
S-transferases, ABC transporters, kinases and biosynthetic genes
of ethylene, JA, lignin and alkaloids. The transcript level of sev-
eral typical pathogens-induced genes (e.g. NBS-LRRs, NDR1)
and genes coding for disease-resistant proteins was induced by
the NO donor SNP (Parani et al., 2004). The transcript level of
several plant defence responses modulating transcription factors,
such as WRKYs, EREBPs (ethylene-responsive element-binding
proteins), several zinc-finger proteins and dehydration-respon-
sive element-binding proteins (DREB1 and DREB2), were also
induced by SNP (Polverari et al., 2003). Zheng et al. (2010) show
that the pretreatment of NO effectively contributed to a better bal-
ance between carbon and nitrogen metabolism by increasing the
total soluble protein and by enhancing the activities of endopep-
tidase and carboxypeptidase in plants under salt stress (Zheng
et al., 2010).
Salicylic acid
The small phenolic compound of SA is a phytohormone, emerg-
ing as a paradigm of an important regulatory role in multiple
