Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 169

spongy mesophyll layers of leaf tissue (Tan et al., 2011).
High temperatures inhibit flower differentiation and
development, and reduce the size of the ovaries of legu-
minous flowers (Johkan et al., 2011). As in other plant
species, HTs also cause oxidative stress by altering the
antioxidant system. In G. max HT (38/28 °C, day/night)
stress resulted in oxidative stress and damaged plasma
membrane, and distorted mitochondrial membranes,
cristae and matrix (Tan et al., 2011). Heat stress
(45/40 °C) created oxidative stress in C. arietinum plants
together with altered activities of antioxidant enzymes
SOD, CAT, APX, GR and concentrations of the non-
enzymatic antioxidants AsA and GSH (Kaushal et al.,
2011). Exposure of V. mungo seeds to 50 °C for 10, 20
and 30 min significantly reduced germination and
vigour index (Piramila et al., 2012).

(Turan & Ekmekçi, 2011). Low temperatures (5 and
10 °C) affected morphological and reproductive attrib-
utes of C. arietinum genotypes. Morphological characters,
viz. plant height, number of branches, number of leaves,
pollen viability percentage, were better in chilling-
tolerant genotypes compared to sensitive genotypes
(Chohan & Raina, 2011). Stylosanthes guianensis , an
important forage legume in tropical and subtropical
regions, is sensitive to chilling stress. The physiological
mechanism of chilling resistance, and the physiological
impact of chilling on antioxidants and photosynthesis in
chilling-resistant mutants and the parent cultivar
CIAT184 were analysed. Chilling temperature reduced
net photosynthetic rate, the maximum photochemical
efficiency, quantum efficiency of photosystem II (PSII)
photochemistry, photochemical quenching efficiency
and excitation energy allocated to PSII photochemistry.
Compared to the parent plant, these values were higher
in mutants (Lu et al., 2013). At low temperatures (6 °C)
for up to 4 days the S. guianensis mutants had higher
activities of SOD, CAT and APX, and higher contents of
AsA and GSH compared to its parental line. These
improved antioxidant systems provided protection for
photosynthesis against chill-induced oxidative damage
and increased chill resistance in mutants (Lu et al., 2013).

11.3.5 Chilling
Studies with some legume species ( Melilotus albus ,
Medicago lupulina , Lotus corniculatus , Trifolium pretense
and T. repens ) with different combination of temperature
treatments revealed that low temperatures negatively
affected the water uptake and germination under unfa-
vourable conditions. Seeds remained impermeable and
dormant until the next favourable season (Van Assche
et al., 2003). Depending upon the sensitivity of varieties
to chilling, low temperature (<10 °C) at flowering has
adverse effects on C. arietinum L. production, which may
cause 15-20% yield losses (Chaturvedi et al., 2009).
Different legumes like field pea, faba bean, lentil and
chickpea were very sensitive to chilling and freezing
temperatures. The reproductive phases, viz. flowering,
early pod formation and seed filling, are most sensitive
to low temperatures. Low temperatures at the repro-
ductive stage may cause flower abortion, poor pod set
and impaired pod filling, and drastic reductions of yield
and quality (Maqbool et al., 2010). In C. arietinum L.
biochemical parameters were adversely affected at low
temperatures (5 and 10 °C); these included increased
electrolyte leakage, total soluble sugars and total free
amino acids. The chilling-tolerant genotypes showed
better performance compared to sensitive genotypes
(Chohan & Raina, 2011). Chilling temperatures (2 and
4 °C) were responsible for causing oxidative stress in
relation to the activities of downregulated antioxidant
enzymes in non-acclimated C. arietinum . However, in
acclimated plants the activities of SOD, APX, GR and
POD increased, which enhanced their chilling tolerance

11.3.6 Flooding
Waterlogging or flooding is damaging for some legumes
such as pigeon pea and soybean. The performance of
two pigeon pea ( C. cajan ) genotypes, ICP 301 (tolerant)
and Pusa 207 (susceptible), was examined under water-
logged conditions. Waterlogging for 4 to 6 days caused
yellowing and senescence of leaves, and decreased leaf
area, dry matter, relative water content and chl content
of leaves. The more severe consequences were observed
in the susceptible Pusa 207 than in ICP 301 (Kumutha
et al., 2009). Waterlogging-induced declines in relative
water content, membrane stability index and chl
content, and increased chl a / b ratio, were greater in the
susceptible Pusa Baisakhi mung bean ( V. radiata ) cul-
tivar than in a T44 (tolerant) cultivar (Sairam et al.,
2009). Soybean plants were subjected to flooded
growing conditions at different growth stages: five
trifoliate vegetative stages, full-bloom flowering stage
and pod fill reproductive stage. Plants were able to with-
stand flooding for 48-96 h without crop injury. Flooding
at the trifoliate vegetative growth stage entailed the
least amount of yield loss. The greatest yield losses