Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 187

caused a sharp increase in Na + concentration in the leaf
apoplast, which was significantly ameliorated by the
addition of Si. Salinity-induced decrease in shoot growth
also recovered upon addition of Si (Shahzad et al., 2013).
In G. max , the addition of Si to salt-stressed plants sub-
stantially alleviated the adverse effects of NaCl on
growth, as it enhanced endogenous GA 3 , while reducing
the levels of ABA and Pro (Lee et al., 2010).

(Ajiboso & Adenuga, 2012). Selenium-induced mitiga-
tion of As stress has been reported by Malik et al. (2012).
When plants were subjected to different levels of As
(2.5, 5.0 and 10 μM), they exhibited drastic reductions
in shoot and root growth and chl content. Arsenic stress
also caused a sharp increase in electrolyte leakage, and
MDA and H 2 O 2 contents. When As-treated plants were
supplemented with Se (5 μM) they showed improve-
ment in growth indicating an antagonistic interaction
between the two elements. The Se-treated plants also
experienced less damage to membranes, chl and cellular
viability induced by As. Moreover, the oxidative damage
due to As was reduced with Se application, which could
be related to the upregulation of antioxidant enzymes
such as SOD, CAT, APX, GR and GST, as well as enhanced
synthesis of water-soluble antioxidants like AsA and
GSH (Malik et al., 2012). Exogenous Se also increased
the metallothioneins (MTs) and thiols under elevated
As, which rendered the plants more tolerant to As. The
beneficial effect of Se on Pb-stressed Vicia faba L. minor
roots was also reported by Mroczek-Zdyrska and Wójcik
(2012). When V. faba roots were exposed to 50 μM Pb,
they exhibited damage due to increased accumulation
of Pb. The added Pb increased the production of O 2 • − ,
lipid peroxidation (MDA content) and thiol content. The
antioxidant metabolism was also altered due to Pb stress.
On the other hand, supplementation of the plants with Se
(1.5 and 6 μM) alleviated Pb toxicity, which was accom-
panied by decreased O 2 • − production in the apical parts of
roots, and increased thiol content and GPX activity.
However, the higher Se concentration intensified MDA
and thiol accumulation and GPX activity in Pb-treated
plant roots. At the lower concentration, Se improved cell
viability, whereas at the higher concentration it was
pro-oxidant and enhanced lipid peroxidation and cell
membrane injury (Mroczek-Zdyrska & Wójcik, 2012).

11.4.7.2 Selenium
Although selenium (Se) has been studied widely in
plants and its beneficial role is well known, it is still
unresolved whether Se is an essential micronutrient for
plants. In many plant species, Se exerts a positive effect
on plant growth and productivity at low concentrations
(Feng et al., 2013). However, the precise mechanisms
underlying the beneficial role of Se in plants have not
been clearly elucidated yet. Some plant species supple-
mented with Se have shown enhanced resistance to
certain abiotic stresses (Hasanuzzaman et al., 2010b,
2011b, 2014c; Hasanuzzaman & Fujita, 2011, 2012b).
Recently, Feng et al. (2013) reviewed the possible
mechanisms responsible for the production and quench-
ing of ROS after Se addition to stressed plants. They
proposed that Se can regulate the ROS levels in stressed
plants through three pathways: (i) by stimulating the
spontaneous dismutation of O 2 • − into H 2 O 2 ; (ii) by a
direct reaction between Se-containing compounds
and ROS; and (iii) by the regulation of antioxidative
enzymes. Another possible mechanism is that Se may
affect the assembly of photosynthetic complexes to reg-
ulate the levels of ROS (Feng et al., 2013).
Ajiboso and Adenuga (2012) investigated the influence
of Se on V. unguiculata and observed that exogenous Se
could alter some biochemical parameters of the plants
under water deficit conditions. Upon exposure to water
deficit for 14 days, V. unguiculata showed a 28.6%
reduction in RWC. Water deficit also caused drastic
increases in MDA levels and antioxidant enzyme activ-
ities. On the other hand, Se-supplemented plants
showed a higher RWC, reduced lipid peroxidation,
further increase in the activities of antioxidant enzymes
such as CAT and GPX, and a higher level of AsA.
Exogenous Se also enhanced some growth parameters
like plant height and number of leaves per plant under
water deficit conditions. Based on the study, Se was rec-
ommended as an antioxidant chemical to be used by
legume growers under conditions of short-term drought

11.5 Conclusion and future
perspectives

Legumes are important for human nutrition and for
maintaining soil fertility. However, there are several
constraints on enhancing the productivity of pulse
crops, including environmental adversities. The situation
is becoming more serious due to the unpredictability of
environmental conditions and global climate change
and variability. Some legumes are very sensitive to