Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 175

compared to untreated stressed plants (Senaratna et al.,
2000). Chilling stress (2 °C) imposed on C. arietinum L.
resulted in several negative impacts on growth and
physiological parameters. But application of 500 and
1000 mM of SA reduced chilling stress effects and
improved plant height, fresh weight, chl content,
relative water content and Pro content, and also reduced
electrolyte leakage compared to chilling stress alone
(Imami et al., 2011). Cadmium stress (50, 100 μM CdCl 2 ;
for 3 and 6 days) reduced the growth of P. aureus and V.
sativa and significantly increased the production of H 2 O 2
and O 2 • − . Seed-soaking pretreatment with 100 μM SA
for 16 h decreased Cd-induced production of H 2 O 2 and
O 2 • − by enhancing activities of symplastic and apoplastic
SOD, symplastic APX and apoplastic CAT under Cd
stress. The SA also improved the growth of these two
species under Cd stress (Zhang et al., 2011). Zhou et al.
(2009) reported that 0.2 mM SA alleviated mercury
(10 μM Hg 2+ ) toxicity, protecting M. sativa roots from
oxidative damage by increasing activities of NADH
oxidase, APX and POD, and by accumulatiion of AsA,
GSH and Pro.

soluble-N, total-N and protein-N contents, and nucleic
acid content. The rates of respiration, O 2 uptake and CO 2
evolution were also reduced, while Na + and Cl − contents
increased and K + , Ca 2+ and Mg 2+ levels decreased. The
exogenous GA improved growth and physiological
attributes and decreased Na + and Cl − contents in root
and shoot (Haleem & Mohammed, 2007). Five levels
of GA (0, 100, 200, 300 and 400 mg/L) were applied as
a foliar spray at 3 and 6 weeks after sowing to assess
the yield and yield traits of different groundnut cultivars
in wet and dry growing seasons. Compared to the
untreated controls, GA increased the yield and yield
components. The highest pod, kernel and haulm yields
were obtained at 100 mg/L GA application both in wet
and dry seasons (Yakubu et al., 2013). Reduced irriga-
tion frequency (at 2-, 4-, 6- and 8-day intervals) in
mung bean drastically reduced plant height, internode
length, number of leaves per plant, leaf area per plant,
leaf area index, number of inflorescences per plant, pod
length, pod number per plant, seed number per pod,
biomass yield and seed yield per plant. Application of
GA 3 (100 and 200 mg/L) with water stress improved
plants' performance regarding these parameters (com-
pared to stress treatment alone), where the combination
of 200 mg/L GA 3 and 2-day irrigation interval showed
the best performance amongst all treatments (Abdel &
Al-Rawi, 2011). Addition of GA 3 also improved germi-
nation and seedling growth of C. arietinum L. cv. PBG-1
under drought stress induced by PEG (Kaur et al., 1998).
Gradual increase of temperature 30 °C, 40 °C reduced
the α-amylase activity in seedlings of different geno-
types of V. radiata. The reduction was greatest at a lethal
temperature of 50 °C. But application of GA 3 (100 μM)
alleviated the effect of heat stress by increasing
α-amylase activity (Mansoor & Naqvi, 2012) and it was
mentioned that elevated α-amylase activity in roots,
shoots and cotyledons was positively correlated with
the progress of seedling growth of mung bean plant.
Cadmium (20 mg/kg CdCl 2 ) and Pb (100 mg/kg lead
acetate) reduced the contents of chls, soluble carbohy-
drates and proteins in V. faba and also in L. albus . Under Cd
and Pb stress bean and lupin plants supplemented with
100 ppm GA showed differential responses. Gibberellic
acid supplementation in broad bean enhanced the activ-
ities of CAT and POD under Pb stress, and amylase activity
under Cd stress. In lupin, GA supplementation enhanced
amylase, CAT and POD activities under Cd stress, and
improved CAT and amylase activities under Pb stress.

11.4.1.3 Gibberellic acid
Gibberellic acids (GAs) constitute a group of phytohor-
mones in higher plants mediating many developmental
processes. Its roles in seed germination, vegetative growth,
flowering induction and fruit development have been
studied extensively (Sun & Gubler, 2004). The results
of previous studies have also proved that GAs have
vital roles in plant responses to biotic and abiotic stress
conditions (Wigoda et al., 2006; Ko et al., 2007; Robert-
Seilaniantz et al., 2007; Navarro et al., 2008).
Hamayun et al. (2010a) reported that exogenous GA 3
application not only enhanced the growth of G. max but
also mitigated the adverse effects of salt stress. The salt
stress mitigation effects of GA 3 application were in regu-
lating the level of phytohormones like bioactive GAs
(GA 1 and GA 4 ) and increasing jasmonic acid (JA), and
decreasing endogenous ABA and SA contents (Hamayun
et al., 2010a). Pre-soaking the seeds in GA 3 (200 mg/L)
was beneficial in minimizing the deleterious effects
of salinity (100, 200 and 300 mM NaCl) in mung bean
plants. The NaCl caused drastic reductions in shoot and
root lengths and their fresh and dry weights, in number
of lateral roots and leaves, and in total area of leaves.
Salinity also reduced pigment contents, photosynthetic
activity, contents of reducing sugars and sucrose, total