Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 171

were burdened with high levels of ROS produced
under UV-B stress that also altered antioxidant and
enzymatic systems as evidenced by decreased CAT and
polyphenol oxidase activities, and increased peroxi-
dase, SOD and phenylalanine ammonia-lyase activities
(Ravindran et al., 2010). After the fifth day of exposure
to UV-B radiation (7 and 9 kJ/m 2 daily doses), shoot
heights of P. sativum were decreased by 58 and 59%, and
leaf area was decreased by 52 and 63% compared to
controls. Shoot dry mass was reduced by 55% under
9 kJ/m 2 of UV-B. Significant decreases of leaf stoma
counts, chl a and chl b contents, chl a / b ratio and carot-
enoid content were also noted under UV-B stress
(Juozaityte et al., 2008). Increased shoot weight and
length, root length and weight, leaf area and number of
nodules were observed due to UV-C treatment of seeds
of groundnut and mung bean (10, 15, 30 and 60 min)
and the reason was a reduction in root-infecting fungi.
The same UV-C treatment also resulted in increments in
total chl and carbohydrate contents (Siddiqui et al.,
2011). Short-term (10, 20 and 30 min) exposure to UV-B
(200-400 nm) radiation enhanced salinity tolerance in V.
radiata (Hamid et al., 2012a).

development and stress signalling, or defense signal net-
working, and influence physiological and biochemical
processes in both synergistic and antagonistic ways. The
adaptive responses of crops under abiotic stresses are
mainly controlled by phytohormones. So, phytohor-
mone homeostasis and signalling are essential for
improving plant performance under stressful environ-
ments (Eyidogan et al., 2012).

11.4.1.1 Abscisic acid
Abscisic acid (ABA) acts as an endogenous messenger in
a plant's perception and adaptive responses to abiotic
stress. It is a chief regulator of plants' water status; it can
specifically target guard cells to induce stomatal closure,
and signal systemically for adjustment in case of severe
water shortage (Swamy & Smith, 1999; Mahajan &
Tuteja, 2005). The signals generated by ABA are vital
throughout a plant's life cycle to control developmental
processes during normal or favourable growth conditions
as well as under stressful conditions. Stress-responsive
genes can be expressed either through an ABA-
dependent or ABA-independent pathway (Chinnusamy
et al., 2004). That is why ABA is known as the plant stress
hormone (Swamy & Smith, 1999; Mahajan & Tuteja
2005).
Drought stress was imposed at the 50% flowering
stage of mung bean plant, and reduced root and shoot
fresh and dry weights. Drought decreased pink bacte-
roid tissue diameter and number of root nodules.
Exogenous ABA (10 −6 M) treatments alleviated the
damage to a great extent and improved drought toler-
ance. The tolerance mechanisms provided by ABA were
increase in chl content and RWC of leaves; increase in
Pro, protein and sugar contents; and enhanced activities
of antioxidant enzymes of leaves. All these contributed
to better performance of the plants and better survival
of Rhizobium in soil following ABA application (Farooq
& Bano, 2006). Abscisic acid (100 μM) alleviated the
harmful effects of drought stress in soybean plant ( G.
max L. cv. Giza 22) by regulating endogenous phytohor-
mones and polyamine contents. Total soluble protein
and the protein banding pattern of soybean was also
improved by ABA (Hassanein et al., 2009). Vicia faba L.
seedlings exposed to water-deficient growing media
showed reduced plant height and root length, root and
shoot fresh weights, and root and shoot dry weights
compared with controls. This stress also reduced total
soluble carbohydrates, chl a and b contents, and

11.4 application of phytoprotectants
for enhancing stress tolerance

Although environmental stresses are considered the
major cause of crop losses in pulses, and most of them are
sensitive to environmental extremes, the mechanisms of
stress tolerance are not yet fully understood and attempts
to improve yield under stress conditions by plant breeding
have been largely unsuccessful, primarily due to the
multigenic origin of the adaptive responses. Exploring
suitable ameliorants or stress alleviants is one of the tasks
of plant biologists. In recent decades, exogenous protec-
tants such as osmoprotectants, plant hormones,
antioxidants, signalling molecules, polyamines and trace
elements have been found to be effective in mitigating
stress-induced damage in plants. These phytoprotectants
can enhance plant growth and yield as well as conferring
stress tolerance (Table 11.4).

11.4.1 phytohormones
Phytohormones are chemical compounds that are pro-
duced in one part of a plant and transported to exert an
effect on another part. They are critical for plant growth,