Agriculture Reference
In-Depth Information
to spd and spm synthesis. spm and spd prevented the leakage of electrolytes and
amino acids from roots and shoots of rice proposing a positive correlation between
salt tolerance and increased accumulation of PAs (Chattopadhayay et al.
2002
). The
protective function of PAs in salt stress may be at least partly due to rigidifying
microsomal membrane surfaces leading to stabilization against NaCl and osmotic
stress (Legocka and Kluk
2005
).
PA effect on salt-stress tolerance can also be attributed to the differential regula-
tion of catabolism of PA by DAO and PAO (Moschou et al.
2008b
; Angelini et al.
2010
). The catabolic products of PA such as 4-aminobutanal, H
2
O
2
and GABA are
associated with various physiological processes involved in stress responses includ-
ing salt stress tolerance. Enhanced DAO/CuAO and PAO activities was observed
in the salt stressed oat seedlings and tomato leaf discs followed by accumulation of
proline and proline accumulation was hindered when these plants were treated with
DAO/CuAO inhibitors (Alcázar et al.
2010b
).
In high salinity exposed soybean roots increase in CuAO and GABA activities
was seen with concomitant decrease in put, cadaverine and spd levels (Xing et al.
2007
). Decrease in CuAO activity, recovery of PA levels and a simultaneous reduc-
tion of GABA level was found in soybean during the recovery from NaCl stress pro-
posing that GABA derived from PA catabolism is probably involved in salt-stress
mediated defence reactions (Xing et al.
2007
). Increased amounts of H
2
O
2
produced
by DAO/CuAO and PAO activities lead to PCD and expression of defence genes
suggesting importance of amine oxidases in salt stress responses. Maize ZmPAO
overexpressing tobacco plants showed high quantities of spd followed by increased
activity of apoplastic PAO. As a result, an elevated amount of H
2
O
2
was produced
and PCD was induced (Moschou et al.
2008a
). In contrast, tobacco plants down-
regulating endogenous PAO accumulated lower amounts of H
2
O
2
in response to salt
stress exhibiting less PCD than wild type plants (Moschou et al.
2008a
). Induction
of several stress-responsive genes could be observed as a result of apoplastic PA
catabolism by PAO (Moschou et al.
2008a
). Moreover, downstream signalling sub-
stances such as mitogen activated protein kinases (MAPK) were induced by H
2
O
2
produced through PAO activity. In maize, salt stress induced ROS generated by
PAO was involved in signalling the adaptive responses to high salinity (Rodríguez
et al.
2009
). These studies indicate that ratio of PA catabolism and anabolism is
crucial in salt stress tolerance.
Taken together, increased PA levels represent a salt-stress induced protective
function in many different plant species. Genetic modification of PA biosynthesis
and catabolism pathways is useful in enhancing salt-tolerance function of model
plants as well as in crop plants.
WaterStress
Drought has a direct effect on agriculture leading to crop losses in different mag-
nitudes in many parts of the world. Far beyond the crop loss, drought causes many
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