Salt stress and leguminous crops: Present status and prospects - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 37

significant enhancement (88%) was observed in roots
due to increased CuZn-SOD isoforms. Roots had
relatively higher APX and GR activities than leaves;
upon salt stress no significant changes in APX, CAT and
GR activities were observed in roots, but APX activity
was higher than in leaves, suggesting that root tissues of
lentil were better protected from NaCl stress-induced
oxidative damage due to enhanced total SOD activity
together with higher levels of APX activity under salinity
stress (Bandeoglu et al., 2004).

to East Asia (e.g., G. tomentella and G. tabacina ). With
cultivation largely concentrated in Latin America and
North America, soybean is an important source of pro-
tein for human and animal nutrition, as well as a major
source of vegetable oil. High levels of salt have negative
impacts on growth, nodulation, agronomy traits, and
seed quality and quantity and thus reduce crop yields.
To cope with salt stress, soybean has evolved several tol-
erance mechanisms, such as (i) maintenance of ion
homeostasis; (ii) osmotic adjustment; (iii) restoration of
osmotic balance; and (iv) other metabolic and structural
adaptations. A review by Phang et al. (2008) integrated
the relevant studies on soybean and proposed a working
model to describe its salt stress responses at the molec-
ular level. Serraj et al. (1994) exposed soybean plants to
short-duration salt stress and reported that the ARA of
salt-stressed nodulated roots fell to 80% within 60 min
after application of 0.1 M NaCl relative to controls.
Salinity-induced dry matter decline is more severe in
the shoot than the root (Shalhevet et al., 1995).
Comba and Benavides (1997) studied the effect of salt
stress on 377 salt-tolerant and 411 relatively sensitive
cultivars of soybean. It was observed that 150 mM NaCl
caused a decrease of 25% in GSH, 50% in GR, 30% in
ascorbate peroxidase (APX), 20% in CAT and 25% in
SOD activities in the sensitive cultivars while there were
increases of 15, 20, 30 and 18% in the tolerant cultivars,
respectively, thereby indicating a correlation between
nitrogen fixation and oxidative stress induced by salt
treatment. Tramontano and Jouve (1997) reported a
five-fold proline increase and a two-fold trigonelline
increase after salt stress in soybean. NaCl significantly
inhibited nitrogenase activity, nodule number and dry
matter accumulation per plant in four soybean cultivars
(Abd-Alla et al., 1998). Comba et al. (1998) reported that
under mild salt stress, the elevated levels of antioxidant
enzymes and decreased glutathione protect nodules
against the activated oxygen species (AOS) thus circum-
venting lipid and protein peroxidation and Lb
breakdown, while severe saline treatment produced a
permanent decay in Lb and nitrogenase activity despite
diminished glutathione levels and GR activity.
Liu and van Staden (2000) selected NaCl-tolerant
lines from callus cultures initiated from soybean cotyle-
dons and reported that salt tolerance in this culture was
characterized by accumulation of Na + , Cl − , proline and
sugars when the plants were grown under salt stress, as
well as on normal media. Garg (2002) reported that

2.4.8 Lupins
The genus Lupinus (commonly known as lupin or
lupine) includes over 200 species, with centres of diver-
sity in North and South America. Yu and Rengel (1999)
reported that salinity stress enhanced the activity of
CuZn-SOD by 14.5% without affecting the activities of
the other SOD forms in narrow-leafed Lupinus angustifo-
lius L.

2.4.9 Groundnut
The genus Arachis comprises about 70 species of annual
and perennial flowering plants. At least one species, the
peanut ( Arachis hypogaea L.), is a major food crop species
of global importance; some of the other species are cul-
tivated for food to a small extent in South America.
Other species such as A. pintoi are cultivated worldwide
as forage and soil conditioning plants, with the leaves
providing a high-protein feed for grazing livestock and a
nitrogen source in agroforestry and permaculture sys-
tems. Jain et al. (2001) observed increased levels of
proline in the NaCl-selected lines of groundnut, which
were probably connected with osmotic adjustments and
the protection of membrane integrity. It was further
observed that addition of proline to the culture medium
improved fresh weight accumulation and reduced per-
oxidative damage to the lipid membranes. Changes in
the ionic relations of salt-sensitive and salt-tolerant cell
lines of groundnut showed a slight increase in Na +
concentration with an increase in NaCl levels (1.3-2.3-
fold); however, the concentration of K + remained
essentially constant (Jain et al., 2001).

2.4.10 Soybean
The best known species of the genus Glycine is the
soybean ( Glycine max L.). The majority of Glycine species
are found only in Australia, and the soybean's native
range is in East Asia. A few species extend from Australia