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high rate of salinity and drought was localized in the extracellular space of soybean
roots. In addition, a lucine like protein was also identified in the mature tissues
of soybean shoot under saline conditions. The production of enzyme, acid phos-
phatase, was related to plant response, under salinity by affecting the formation of
reactive oxygen species as well as by affecting the transduction pathways, related
to stress (Liao et al.
2003
; Sobhanian et al.
2010
). The salt responsive gene,
Gm-
DREB2
, was expressed under salinity stress, resulting in the production of higher
levels of proline, relative to the wild types, improving plant tolerance to salinity
stress (Chen et al.
2007
). It has been indicated that soybean genotypes, which are
tolerant to salinity have the same gene (Lee et al.
2004
).
Relative to the wild types, the salt tolerant of soybean genotypes was due to the
inhibition of Cl
−
transport from the soybean roots to the shoots. However, in the
wild variety the tolerance was more related to the prevention of Na
+
movement
from the plant roots to the aerial parts. This indicates that salt tolerance in the ge-
netically modified varieties have been improved relative to wild types (Lee et al.
2009
).
Under stresses like salinity and drought the level of proline increases in soybean
nodules, as its synthesis is enhanced. High proline accumulation in the nodules
results in the high ratio of NADP/NADPH and hence the activation of pentose phos-
phate pathway and eventual production of purine. The derivatives of purine can act
as transporters of fixed N. Proline can be the transporter for the redox potential from
plant cytoplasm to the bacteroid, verified by the high activity of pro dehydrogenase
in the bacteroids of root nodules (Kohl
1988
,
1990
; Verbruggen and Hermans
2008
;
Sharma and Yadav
2012
).
Although plant morphological and physiological properties are altered by salin-
ity stress, the role of plant hormones is among the most important mechanisms
by which plant can alleviate the stress of salinity (Velitcukova and Fedina
1998
).
Accordingly, the production of several proteins during salinity stress is induced by
plant hormones such as jasmonates (Chao et al.
1999
; Thaler
1999
), salicylic acid
(Hoyos and Zhang
2000
) and abscisic acid (Jin et al.
2000
; Wang et al.
2001
; Kang
et al.
2005
; Miransari
2012a
).
Yoon et al. (
2009
) found that salinity stress significantly decreased plant
growth, gibberellins concentration, rate of photosynthesis and transpiration, and
considerably increased ABA production as well as proline accumulation. How-
ever, application of methyl jasmonate (MeJA) significantly alleviated the stress
of salinity on soybean growth, chlorophyll, photosynthesis and transpiration rate,
and proline content, while enhancing the level of ABA and gibberellins (Miran-
sari
2012a
).
Calreticulin is a protein, which is able to bind calcium, and hence regulates cal-
cium homeostasis and protein folding in the plant endoplasmic reticulum. Under
salinity, osmotic stress resulted in the down regulation of calreticulin in rice, indi-
cating the role of calcium under salinity stress as the main secondary messenger.
Salinity also down regulated the activity of RuBisco activase, adversely affecting
photosynthesis (Menegazzi et al.
1993
; Rokka et al.
2001
; Sobhanian et al.
2010
).
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