Agriculture Reference
In-Depth Information
rice (Li and Chen
2000
), where even a fall in SAMDC1 was registered 12 h after rice
plants were treated with ABA. The decline in transcripts was assigned to changes in
mRNA stability (Li and Chen
2000
). The gene induction patterns triggered by ABA
in cacao leaves and roots disagree with those observed in other plant species. ADC2
was highly induced by ABA (50 mM) in
Arabidopsis
(Pérez-Amador et al.
2002
).
Also in
Arabidopsis
, Alcázar et al. (
2010
) observed that ADC2, SPMS, and SPDS1
were highly induced by drought and greatly reduced by this stress in ABA insensi-
tive mutants
.
ABA triggered significant alterations in the PA catabolic pathway of
grapevine leaf, but at the same time, it also induced the activity of biosynthetic
enzymes ADC, ODC, and SAMDC (mainly in the tolerant genotype), justifying the
interplay between PA anabolism and ABA signaling pathways in grapevine (Toumi
et al.
2010
). This induction (which took place within 1 h post-treatment) resulted
in different enzyme induction patterns in the tolerant and sensitive genotypes, with
the sensitive genotype responding lately and less profoundly. On the other hand,
PAs oxidation concerned PAOs in the tolerant genotype and DAOs in the sensi-
tive genotype. On the basis of this information, the following model was proposed:
PA biosynthesis is higher in the tolerant than in sensitive grapevine genotypes; in
both genotypes, PAs follow the exodus route and are catabolized in the apoplast by
AOs, producing H
2
O
2
; in the case of high intracellular PA titers/PA anabolism, toler-
ance is enhanced via induction of additional defensive genes/responses; in the case
where PA titers/PA anabolism is low, H
2
O
2
enhances the PCD syndrome.
It has been shown that nitric oxide (NO)-treated plants have increased tolerance
to drought (Garcia-Mata and Lamattina
2001
,
2002
). Arasimowicz-Jelonek et al.
(
2009
) demonstrated the occurrence of a functional crosstalk between PAs and NO
in cucumber leaves under drought stress. Although exogenous PAs (1.0 mM Spd,
Spm, and Put) did not affect NO production in well-watered cucumber seedlings,
their treatment with Spm and Spd, prior to water deficit imposition, induced early
and higher NO levels (noticed by NO-dependent fluorescence) in leaves of drought-
stressed cucumber plants, with respect to the control and Put treated ones.
Recently, Alcázar et al. (
2010
) discussed advances in the crosstalk between PAs
and ABA, integrating them with other abiotic stress-related metabolic routes such
as reactive oxygen species (ROS) signaling, generation of NO, modulation of ion
channel activities and Ca
2+
homeostasis.
5.2 Saline Stress
First reports on the induction of plant PAs metabolism over salt stress, as well as
its possible alleviating role on plant salt tolerance can be traced back to the eighties
(20th Century). Many authors have reported that PAs accumulation is the immedi-
ate response observed in different crop plants species after exposure to saline condi-
tions (Erdei et al.
1996
; Chattopadhyay et al.
2002
; Ghosh et al.
2011
). Most sig-
nificant changes in polyamines level upon salinization appear to be those of Spm,
according to data reported in rice (Maiale et al.
2004
), maize (Jiménez-Bremont
