Agriculture Reference
In-Depth Information
a matter of debate (Groppa and Benavides
2008
). Under NaCl-induced stress, a
higher level of lipid peroxidation was observed in the salt sensitive, relative to the
salt-tolerant wheat (El-bassiouny and Bekheta
2005
) and rice (Roychoudhury et al.
2008
) cultivar, which showed augmented Spd and Spm levels, not observable in the
salt sensitive cultivars.
Xing et al. (
2007
) analyzed the effects of treatments with different NaCl con-
centrations, with or without aminoguanidine (AG; a specific DAO inhibitor) on
endogenous free PAs, GABA accumulation and DAO activity in soybean roots
(
Glycine max
(L.) Merr., cultivar Suxie-1). Results showed significant Put, Cad and
Spd decreases with increasing salt concentrations, assignable to the promotion of
DAO activity by salinity and consequent stimulation of PAs degradation. In paral-
lel, GABA accumulation raised with growing NaCl concentrations, strongly sug-
gesting its origin in PAs degradation.
Reactive oxygen species are necessary in many plant developmental processes
(Foreman et al.
2003
; Demidchik and Maathuis
2007
), particularly in the elongation
zone of maize leaves during leaf extension (Rodríguez et al.
2002
). In plants of this
species, the salt-induced decrease of extracellular ROS contributes to the reduction
of leaf elongation (Rodríguez et al.
2004
). In turn, the diminution of the extracel-
lular ROS has been attributed to the inhibitory effect of NaCl on the NADPH oxi-
dase complex (Rodríguez et al.
2007
). Rodríguez et al. (
2009
) reported that under
saline stress, extracellular ROS registered in the elongation zone of maize leaves
are produced principally by PAO, contributing partially to counteract the growth-
inhibiting effect caused by salinity. In turn, this same phenomenon was described
in soybean hypocotyls grown under NaCl stress (Campestre et al.
2011
). In the last
species, saline stress increased Spm and Cad level and CuAO activity. Treatment
with the CuAO inhibitor showed a significant reduction of ROS in the elongation
zone and plants grown in Cad-amended culture medium showed longer hypocotyls
in saline condition (relative to the unamended treatment), effect that was abolished
by the CuAO inhibitor. Since H
2
O
2
functions as a signal molecule activating many
of the plant responses deployed to cope with stress, it is believed that its generation
from PAs oxidation (along with PA depletion) might orchestrate (at least partially)
plant adaptation to these conditions (Moschou et al.
2008
; Rodríguez et al.
2009
).
5.3 Cold Stress
In temperate climates, plant species have acquired a certain degree of cold toler-
ance, depending on the genetic background, cold hardness and exposure time (Jan-
ská et al.
2010
). Plant physiologists use the term freezing to mean temperatures
below 0 °C, chilling for temperatures between 0 °C and the minimum temperature
necessary for growth, and temperature between that minimum and the optimum is
denominated suboptimal temperature for growth. Such a difference in stress ter-
minology is not trivial, since the physiological response of a plant species may be
different in each case. Temperate and tropical crop species such as rice, maize and
