Salt stress and leguminous crops: Present status and prospects - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 36

nitrogen-fixing crop. Pigeon peas are very drought
resistant and the crop is cultivated on marginal land by
resource-poor farmers.
Shiva Prakash and Sarin (1993) have described a
positive correlation between the Na + level and proline
concentration in the salt-tolerant cell lines of C. cajan .
Increased Na + levels in shoots and roots of C. cajan plants
exposed to salinity have been reported by Gill and
Sharma (1993). Accelerated nodule greening supple-
mented by a concomitant reduction in Lb content of the
nodules and ARA were observed when 45-day-old
chickpea plants were subjected to 50 and 100 mM NaCl
treatments for 7 and 14 days, respectively (Sheokand
et al., 1995). Similar observations have been reported in
pigeon pea (Garg & Dua, 1996; Swaraj et al., 2000).
Bishnoi et al. (2006) observed changes in the protein
profile of pigeon pea genotypes Manak (salt-tolerant)
and ICPL 88039 (salt-sensitive) to stress of 3 mM
boron + 60 mM NaCl. The appearance was reported of
95.6 kDa proteins in plumule and 67.5 kDa proteins in
the radicle of Manak under NaCl treatment with no
specific protein in ICPL 88039.
Arbuscular mycorrhizal (AM) fungi occur extensively
in natural ecosystems as well as in salt-affected soils and
are proven suitable candidates for bioamelioration of
saline soils. Plants respond to salinity by building up
sugars and other low-molecular-weight compatible sol-
utes. An investigation was carried out to evaluate the
effect of interactions between an AM fungus and salinity
stress on growth, nitrogen fixation and trehalose metabo-
lism in two genotypes of pigeon pea, namely Sel 85N
(salt-tolerant) and ICP 13997 (salt-sensitive) (Garg &
Chandel, 2011). Salinity reduced plant biomass (shoot
and root) in both genotypes and also caused a decline in
shoot-to-root ratio (SRR). However, a slight decline was
observed in Sel 85N compared to ICP 13997. Colonization
by AM fungus was reduced with increasing salinity levels
but mycorrhizal responsiveness (MR) was enhanced.
Genotypic variability in nitrogen fixation and trehalose
metabolism in response to salinity and mycorrhization
was also noticed. An increment in nodule number was
associated with a reduction in dry mass. Subsequently,
nodular activity (leghaemoglobin, ARA, nitrogen content)
was reduced under soil salinity, the reduction being more
profound in ICP 13997 than in Sel 85N. A symbiotic rela-
tionship between plant roots and Glomus mosseae caused
salinity tolerance in a genotype-dependent manner in
pigeon pea (Garg & Chandel, 2011).

Proline functions as an osmoprotectant and plays
an important role in osmotic balancing, protecting
subcellular structures and enzymes, and in improving
cellular osmolarity to provide the turgor necessary
for cell expansion under stress conditions. The enzyme
delta-1-pyrroline-5-carboxylate synthetase (P5CS), a
rate-limiting enzyme in proline biosynthesis that is
known for convening improved salt and drought stress,
is subject to feedback inhibition by proline. Transgenic
pigeon pea plants were developed using efficient in vitro
transformation of embryonic structures and Agrobacterium
tumefaciens strain and the Vigna aconitifolia P5CSF129A
genes under a constitutive 35S promoter. The resultant
primary transgenic plants exhibited more build-up of
proline than their non-transformed plants. Levels of
proline were also raised in T1 transgenic plants when
grown in the presence of 200 mM NaCl. In addition to
their improved growth performance, elevated chloro-
phyll and relative water content under high salinity,
these plants also had reduced levels of lipid peroxida-
tion. This study revealed that overproduction of proline
might play an important role in protecting against salt
shock and cellular integrity in pigeon pea (Surekha
et al., 2014).

2.4.7 Lentils
The genus Lens contains four species of small, erect or
climbing herbs with pinnate leaves and small inconspic-
uous white flowers and small flattened pods. The lentil
( Lens culinaris ) is a bushy annual plant grown for its
lens-shaped seeds. Ashraf and Waheed (1993) reported
that leaf soluble proteins decreased due to salt stress in
all lines of lentil, irrespective of their salt tolerance.
Studies done by Rai and Singh (1999) indicated that the
interactions between salt-tolerant lentil genotypes and
Rhizobium strains were significant and resulted in greater
nodulation and N 2 fixation (nitrogenase activity) in
sodic soils compared to uninoculated controls.
Bandeoglu et al. (2004) evaluated the growth
performance of lentil under NaCl-salinity stress and
reported considerable reduction in shoot/root length
and fresh/dry weights of the plants. Levels of H 2 O 2 , lipid
peroxidation and electrolyte leakage were enhanced
under NaCl salinity in leaves of lentil, whereas roots
were less affected. Leaves had CuZn-SOD, Fe-SOD and
Mn-SOD activity, whereas Fe-SOD activity was missing
in root extracts. Salt stress did not cause a significant
increase in total SOD activity of leaf tissues but a