Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 181

Toxic
metals

H 2 O 2

ROS

Toxic
metals

H 2 O

e -

e -

H 2 O 2

e -

PCS

GPX PC

GSH Metals

H 2 O

Toxic
xenobiotics
including
metals

PC-metals

GST

Vacuole

Cytosol

Figure 11.3 Glutathione-mediated toxic metal and xenobiotic detoxification in plant cells. AsA, ascorbic acid; GPX, glutathione
peroxidase; GSH, glutathione; GST, glutathione- S -transferase; PC, phytochelatin, PCS, phytochelatin synthase; ROS, reactive
oxygen species.

cv. Binamoog-1) seedlings were exposed to salt stress
(NaCl, 200 mM), which disrupted the antioxidant system
components resulting in oxidative stress. Exogenous
GSH reduced the oxidative stress, marked by reduced
MDA and H 2 O 2 levels. GSH application decreased
oxidative stress by increasing activities of antioxidant
enzymes, contents of GSH and AsA, and the GSH/GSSG
ratio, and decreasing GSSG content (Nahar et al., 2012).
Drought stress imposed on V. radiata cv. Binamoog-1
seedlings increased the oxidative stress; deleterious
effects were more severe with 48 h duration, compared
to 24 h duration. However, exogenous co-application
of GSH with drought stress enhanced the antioxidant
system, which included enhanced activities of APX,
MDHAR, DHAR, GPX and CAT. Thus, GSH reduced the
oxidative damage by reducing lipoxygenase activity and
MDA and H 2 O 2 levels under drought stress. Exogenous
GSH also enhanced the activities of glyoxalase enzymes,
which are required for methylglyoxal detoxification
(Nahar et al., 2013). GSH has also proved to be a potent
protectant against heavy metal stress. Seedlings of mung
bean ( V. radiata cv. Binamoog-1) showed damage due to

cadmium (CdCl 2 , 1 mM) toxicity. Protection from
oxidative damage induced by Cd was achieved by appli-
cation of GSH (1 mM). The exogenous GSH improved
the endogenous GSH level and GSH/GSSG ratio,
decreased GSSG, and increased the activities of antioxi-
dant enzymes MDHAR, DHAR and GR. The reduced
oxidative stress due to exogenous GSH was also partly
achieved by the enhanced glyoxalase system as
evidenced by increased Gly I and Gly II activities (Nahar
et al., 2012).

11.4.4.2 Ascorbic acid
Ascorbic acid (AsA) is one of the key components
of the antioxidant defence system, acting as a redox
buffer in plant cells. It plays significant roles in plant
growth, metabolism, development and stress responses
(Noctor & Foyer, 1998; Anjum et al., 2012a,b, 2014;
Alam et al., 2014b). AsA protects the plasma membrane
against oxidative damage and is a precursor for some
plant metabolites (Smirnoff, 1996; Noctor & Foyer,
1998), helping in the regeneration of α- tocopherol and
zeaxanthin, and in PSII activity (Smirnoff, 1996). It has