Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 182

roles in controlling cell cycle progression (Potters et al.,
2002) and root growth and development (Liso et al.,
2004). The protective effects of AsA under different
stress conditions in different plant species show that
the levels of not only AsA but also the AsA-GSH cycle
components, both enzymatic and non-enzymatic, are
often correlated with and confer environmental stress
tolerance (Hasanuzzaman et al., 2012c; Nahar et al.,
2012, 2013).
Salt stress (100 and 400 mM NaCl) in P. vulgaris cv.
Naz enhanced oxidative stress. Exogenous AsA (25, 50
and 100 mM) modulated antioxidant enzyme activities
(SOD, CAT, APX, GR and POD), reduced oxidative
stress, prevented lipid peroxidation and decreased gen-
eration of MDA, thereby enhancing salt stress tolerance.
AsA also reduced exogenous ABA generation under
NaCl. Under salt stress different doses of AsA increased
the maximum photochemical efficiency of PSII, com-
pared to NaCl stress alone (Dolatabadian & Jouneghani,
2009). Beltagi (2008) reported that C. arietinum plants
treated with NaCl (40 mM) suffered adverse effects on
their photosynthetic pigments. Exogenous AsA treat-
ment improved the chl a content and chl stability index.
Exogenously applied AsA (400 mg/L, 4 h) counteracted
the adverse effects of salt stress (12.5 and 50 mM NaCl),
improved antioxidant enzyme activities (CAT, POX,
SOD) and improved germination and growth perfor-
mance of G. max seedlings (Dehghan et al., 2011). Water
stress (−1 MPa) reduced N fixation and carbon flux in
nodules of P. sativum , but 5 mM AsA with water stress
(−1 MPa) increased the nodule AsA + dehydroascorbate
(DHA) pool compared to water-stressed nodules without
AsA, modulated guaiacol peroxidase activity in leaves
and nodules, restored nodule carbon and N enzymes,
and prevented the decline in N fixation and the
reduction of carbon flux in nodules (Groten et al., 2006).
The N 2 -fixing legume nodules of G. max are vulnerable
to oxidative damage caused by leghaemoglobin, which
produces ROS through spontaneous autoxidation.
Treatment of G. max with excess AsA with irrigation
increased nitrogenase activity, nodule leghaemoglobin
content, and activity of APX. The concentration of lipid
peroxides, an indicator of oxidative damage and onset
of senescence, was reduced by exogenous AsA. Thus
exogenous AsA decreased oxidative stress and improved
capacity to fix N 2 (Bashor & Dalton, 1999). Nodule
development and senescence in P. vulgaris is partly
controlled by endogenous AsA or its associated

enzymes. P. vulgaris treated with salt (150 mM NaCl),
Cd (100 μM CdCl 2 ) or oxidative stress (10 mM H 2 O 2 )
showed that under these stress conditions or in natu-
rally senescing nodules the AsA level and associated
enzyme activity decreased (Loscos et al., 2008). Balanced
AsA, DHA, GSH and GSSG pools with higher activities
of DHAR and MDHAR helped in controlling Cd-induced
oxidative stress in V. radiata plants (Anjum et al., 2011).
In another study, Nahar et al. (2012) proved that ele-
vated AsA levels together with enhanced concentration
of other components of the AsA-GSH cycle were
involved in increasing oxidative stress tolerance in
V. radiata seedlings under salt, drought and Cd stress
conditions. Exogenous applications of the AsA precursor
l -galactono-1,4-lactone (Gal, 50 mM) were effective in
protecting thylakoids from oxidative damage caused
by paraquat (Tambussi et al., 2004). In a recent report,
Alam et al. (2014b) investigated the roles of AsA (1 mM)
under osmotic stress (induced by 15% PEG-6000) by
examining morphological and physiological attributes,
antioxidant defence and the glyoxalase system in Brassica
species ( B. juncea, B. napus and B. campestris ). Osmotic
stress reduced fresh and dry weights, leaf RWC and chl
content; and increased Pro, MDA and H 2 O 2 contents and
LOX activity. The ascorbate content in B. napus, B. campes-
tris and B. juncea decreased, increased and remained
unaltered, respectively. The dehydroascorbate content
increased only in B. napus , and the AsA/DHA ratio was
reduced by osmotic stress in all species except B. juncea .
Osmotic stress increased GSH content only in B. juncea ,
increased GSSG content and decreased the GSH/GSSG
ratio in all species. Osmotic stress increased activities of
APX (except in B. napus ), GR (except in B. napus ), GST
(except in B. juncea ) and GPX, and decreased the activ-
ities of CAT (in all species) and of MDHAR (only in
B. campestris ). Osmotic stress decreased glyoxalase I (Gly
I) and increased glyoxalase II (Gly II) activity. Addition of
AsA in combination with PEG improved fresh weight,
RWC and chl content; and decreased Pro, MDA and H 2 O 2
levels. It improved levels of AsA-GSH cycle components,
and improved the activities of all antioxidant and glyoxa-
lase enzymes in most cases. So, exogenous AsA improved
physiological adaptation and alleviated oxidative damage
under osmotic stress by improving the antioxidant and
glyoxalase systems in all species, with B. napus showing
greater antioxidant capacity. The performance of B. juncea
was also better in response to exogenous AsA addition
under osmotic stress (Alam et al., 2014b).