Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 185

reduced the contents of K, Ca, Mg, Mn and Zn, while
the contents of Cu and Fe were increased. However,
when the seedlings were supplemented and grown
under Ni stress, soluble protein and Pro contents
decreased. Nitric oxide supplementation also increased
the SOD activity and eliminated the Ni-induced inhibi-
tion of POD and CAT activities. Although exogenous NO
had no effect on the impact of Ni on K, Cu, Fe and Mn
concentrations, it did improve the Ca and Zn concentra-
tions in Ni-treated seedlings. These results suggested
that exogenous NO efficiently attenuates oxidative
stress in P. vulgaris , but could not prevent Ni-induced ion
leakage. Cai et al. (2011) reported that exogenously
NO could protect soybean plants from Al-induced
oxidative stress due to the enhancement of the antioxi-
dant defence induced by the NO donor. Soybean plants
exposed to Al (50 μM AlCl 3 ) showed a significant
reduction in root elongation and a slight reduction in chl
content, which was associated with higher Al content in
roots. Aluminum treatment also resulted in slight
increases in SOD and CAT activities, while POD activity
decreased with a concomitant increase in MDA content.
On the other hand, the seedlings pretreated with NO
donor (0.25 mM SNP) showed improvement in root
elongation and chl content, upregulated the activities
of the antioxidant enzymes and reduced lipid peroxi-
dation. The protective effects of SNP were reversed
by the addition of an NO scavenger - 50μM cPTIO,
2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazo-
line-1-oxyl-3-oxide - which confirmed the obvious role
of NO in Al stress in soybean (Cai et al., 2011). When
chickpea plants were sprayed with NO donor (150 and
300 μM SNP) they performed well under chilling stress,
with improvements in plant height and leaf area,
decreased electrolyte leakage, and improved yield com-
ponents and final yield of the crop (Chohan et al., 2012).
They also observed that the effects were different in
chill-sensitive and chill-tolerant genotypes, and that the
lower concentration of SNP (150 μM) was more effective
than the higher concentration (300 μM).

In V. radiata , foliar application of Zn provided better
protection against water stress (Thalooth et al., 2006).
When the bean plants were subjected to lack of irriga-
tion, whether at vegetative, flowering or pod formation
stages, significant reductions were seen in all growth
parameters, yield components and photosynthetic
pigment content compared with unstressed plants.
However, foliar application of Zn in water-stressed
plants improved growth parameters, yield and yield
components (Thalooth et al., 2006). The protective effect
of Zn and B in mitigating salt stress in V. radiata was
reported by Arora et al. (2012). Different levels of
salinity (10, 20, 40, 60, 80, 100 and 200 mM NaCl)
resulted in decreases in seed germination as well as in
growth parameters such as root length, shoot length,
number of branches per plant and dry weight of
V. radiata plants in dose-dependent ways. However,
when different combinations of Zn (1 to 10 μM) and B
(1 to 5 μM) were applied, the negative effects of salt
stress were partially mitigated and provided improved
plant growth. Concentrations of 4 μM Zn and 3 μM B
were found to be optimal in mitigating salt stress in
V. radiata (Arora et al., 2012). The protective effect of Zn
was also reported in Cd-stressed V. radiata (Kumari et al.,
2011). When V. radiata plants were exposed to Cd
(0.2 mg/L), there were significant reductions in growth
parameters like plant height, fresh weight of plants,
number of root nodules, and chl a and b contents, and in
biochemical parameters like NR activity, glutamine oxo-
glutarate aminotransferase activity, and protein content.
However, these growth and biochemical parameters
were increased by combined treatment with Zn and Cd
compared to Cd treatment alone (Kumari et al., 2011).
Patel et al. (2013) reported that exogenous application
of Zn on P. aureus could partially restore seedling growth
and reduce oxidative stress during seed development at
low concentrations of the heavy metals Cd and As (25
and 50 mg/kg), while the Zn could not protect the seed-
lings from higher concentrations of Cd and As. The
Zn-induced alleviation of Cd and As toxicity was associ-
ated with an enhanced level of free Pro and improved
metal-chelating activity as well as the higher antioxi-
dant defense system in P. aureus seedlings (Patel et al.,
2013). Bellaloui (2011) reported that soybean plants
grown under waterlogged conditions and supplemented
with foliar application of boron (B) improved their seed
protein, oil, fatty acid and nitrogen metabolism com-
pared with plants that did not receive B. In a subsequent

11.4.6 Micronutrients
Although the main role of micronutrients is to make plants
healthy and ensure that their life cycle runs smoothly, the
management of plant micronutrients is very helpful in
developing plants' tolerance to several abiotic stresses.
Better use of micronutrients can effectively alleviate stress-
induced damage by improving several defence systems.