Agriculture Reference
In-Depth Information
the drier regions of the tropics, where other food
legumes do not perform well. This species also has the
useful capacity to fix atmospheric nitrogen through its
root nodules, and it grows well in poor and marginal
soils containing more than 85% sand, 0.2% organic
matter and low levels of phosphorus. In addition this
crop is considered an important component of tradi-
tional intercropping systems, especially in the complex
and elegant subsistence farming systems of the dry
savannahs in sub-Saharan Africa (Sanginga et al., 2003;
Singh et al., 2003).
Corpas et  al. (1991), in studies with cowpea plants
under salt stress, recognized the subcellular location of
three SOD isozymes present in leaves (Mn-SOD, CuZn-
SODI and CuZn-SODII). Hernandez et  al. (1995)
reported that in the leaves of salt-stressed cowpea
plants, mitochondrial Mn-SOD was considerably
reduced, whereas cytosolic and mitochondrial CuZn-
SODI was marginally reduced and chloroplastic
CuZn-SODII did not display a response. In protoplasts,
Mn-SOD showed considerably reduced activity, CuZn-
SODII was distinctly inhibited and CuZn-SODI exhibited
an intermediate sensitivity.
Sousa et  al. (2003) studied the protein pattern in
cowpea seedlings subjected to salinity (100 mM NaCl)
by isolating the albumins from stems and leaves; they
reported that in stem, 19 proteins (14.6-76.3 kDa) had
their relative concentration augmented by salinity, eight
(31.2-65.0 kDa) had their relative concentration
decreased by salinity and nine (16.3-39.8 kDa) were
apparently synthesized de novo , while in the leaves nine
(18.2-33.2 kDa) proteins increased in concentration,
one (17.1 kDa) decreased in concentration and one
(21.2 kDa) was apparently synthesized de novo .
Twenty-five genotypes of cowpea were tested for salt
tolerance at the vegetative growth stage at salinity levels
of 0, 85 and 170 mM NaCl. The genotypes were classi-
fied based on plant survival, ion concentration (Na + and
Cl ) in root and shoot, and biomass accumulation.
Biomass accumulation was affected by both 85 and
170 mM NaCl in all groups of genotypes; however, salt-
tolerant and moderately salt-tolerant genotypes
displayed more biomass than genotypes classified as
moderately salt-sensitive and salt-sensitive. In all geno-
types Cl concentration was greater in shoots than roots,
and became enhanced as salinity increased. Similarly
Na + concentration amplified with increasing salinity.
However, in salt-tolerant and moderately salt-tolerant
genotypes, Na + concentration was more in roots than
shoots, while in moderately salt-sensitive and salt-sensitive
genotypes, Na + was higher in shoots than roots (Murillo-
Amador et al., 2006).
A study was conducted by Wilson et al. (2006) to see
the effect of salinity on leaf gas exchange by deter-
mining net photosynthetic rate per unit leaf mass (Pnm)
and per unit leaf area (Pna), and stomatal conductance
(gs) of the four cowpea cultivars. The study revealed a
highly significant reduction of Pnm, Pna and gs due to
salinity. Pnm was more sensitive to salinity than Pna. It
was found that increasing stomatal closure with
increasing salinity might limit Pnm or Pna. There was
no significant difference of Pnm and Pna among the
four cultivars, while a significant difference was found
only for gs. No significant salt × cultivar interaction
effect was found with Pnm, Pna and gs, demonstrating
that the four cowpea cultivars have the same response
pattern of leaf gas exchange to salinity (Wilson et  al.,
2006).
Cavalcanti et  al. (2007) reported that cowpea roots
and leaves present different mechanisms of response to
lipid peroxidation and CAT and SOD activities during
salt stress and recovery. However, these responses were
not connected with the growth reduction in cowpea.
The alternative oxidase (Aox) was studied at different
levels (transcript, protein and capacity) in response to
an osmotic shock applied to roots of two cowpea culti-
vars, Vita 3 and Vita 5, tolerant and sensitive to drought/
saline stress respectively. The VuAox1 and VuAox2a
mRNA were not detected in either cultivar under all
tested conditions while the VuAox2b gene was differen-
tially expressed. Upon salt stress, the VuAox2b gene was
overexpressed. At 100 mM NaCl, this VuAox2b gene
overexpression led to a higher amount and capacity of
Aox. This effect was reduced at 200 mM NaCl (Costa
et al., 2007).
2.4.6 pigeon pea
Pigeon pea, Cajanus cajan (L.) Millsp., is the sixth most
important grain legume crop of rain-fed agriculture. Pigeon
peas are cultivated in more than 25 tropical and subtropical
countries either as sole crops or intermixed with cereals.
Pigeon peas are both a food crop (for dried peas, flour or
green vegetable peas) and a forage/cover crop. In
combination with cereals, pigeon peas make a well-
balanced human food. The plant plays an important role
in subsistence agriculture as fodder, fuel and symbiotic
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