Exogenous application of phytoprotectants in legumes against environmental stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 168

percentage, vigour index, plumule length and radicle
length were decreased after Pb exposure in dose-depen-
dent ways. For instance, the germination percentage
was decreased from 98.5% to 32.8% upon exposure to
4.5 mM PbCl 2 . These elevated level of Pb also decreased
the vigour index to 175.4, compared with 1027.4 in
control plants. However, all of these parameters varied
greatly within genotypes. Fatoba et al. (2012) deter-
mined the comparative response of both Arachis hypogaea
and G. max grown in soil with different levels of Cd
and Pb (10, 20, 30 and 40 mg/kg). These metals at high
concentrations (40 mg/kg) caused drastic reductions
in germination, growth and productivity. Cadmium
treatment at 10 mg/kg concentration produced a
significant ( P < 0.05) effect on seed germination in A.
hypogaea and G. max. Increasing the concentration to
30 mg/kg reduced the numbers of leaves, leaf area,
number of pods per plant and number of seeds per plant
(Fatoba et al., 2012). However, further increasing the
concentration of Cd to 40 mg/kg drastically reduced all
the growth indices significantly compared to the con-
trols. In G. max a lead concentration of 20 mg/kg greatly
affected the leaf area, number of pods per plant and
number of seeds per plant, while a significant effect was
recorded in A. hypogaea under a regime of 10 mg/kg in
number of leaves, height, leaf area and number of seeds
per plant (Fatoba et al., 2012). Both Cd and Pb at 30 mg/
kg resulted in a great reduction in the leaf sizes in G. max
and A. hypogaea . Different toxic metals also cause
oxidative stress in plants, which is a general phenomenon
for both redox-active or non-active metals. As reported
by Saidi et al. (2013), exposure of P. vulgaris to 20 μM Cd
resulted in significant decreases in chl and carotenoid
concentrations, with concomitant enhancement of elec-
trolyte leakage, H 2 O 2 content and accumulation of
MDA. Plants exposed to Cd also showed impairment
of antioxidant metabolism. While studying L. culinaris ,
Janas et al. (2010) observed a sharp reduction of growth
and increased lipid peroxidation and H 2 O 2 accumulation
when the plants were exposed to copper (Cu) at vari-
able concentrations (0.05, 0.1 and 0.5 μM).

massive food insecurity (Bita & Gerats, 2013). High-
temperature stress results in detrimental effects on
legumes, but the adverse temperature range varies for
different kinds of legume. The maximum threshold seed
zone temperature for the emergence of V. unguiculata is
about 37 °C. Among the growth stages, the reproductive
phase of plants is highly sensitive to HT stress, and plant
fertility is considerably reduced with increases in tem-
peratures. Pre-anthesis heat stress in P. vulgaris caused
anomalous pollen and anther development (Porch &
Jahn, 2001). Heat stress caused abscission and abortion
of flowers, young pods and developing seeds in soybean.
Lower pollen viability at 37/27°C (day/night) reduced
pod setting in soybean (Kitano et al., 2006). The heat
stress tolerance of four A. hypogaea cultivars was investi-
gated; the HT stress (28/22 or 38/22°C from 21 to 90
days after planting) reduced total dry weight by 20 to
35%, and the seed harvest index by 0 to 65% (Craufurd
et al., 2002). Cicer arietinum exposed to 35/16°C (day/
night for 10 days) during flower and pod development
stages reduced the number of pods per plant by 53%
and seed yield by 48% (Gan et al., 2004). High-
temperature stress at pre-anthesis may reduce pollen
viability and germinability, and these factors were inves-
tigated as common reasons for poor fruit set in legumes
including common bean and peanut (Gross & Kigel,
1994; Kozai et al., 2004). Heat stress reduced the chl a
content of L. esculentum leaves by 10-32%, chl b by 10%
and chl a / b by 5%, which was the reason for the
reduction of photosynthesis (Malgorzata et al., 2009). In
P. vulgaris phenology, partitioning, plant-water rela-
tions, and shoot growth and extension were all
hampered by heat stress (Koini et al., 2009). At normal
temperatures, seeds of Cassia tora exhibited 92% germi-
nation. But at 40, 50 and 60 °C (for 10 days) the
germination percentages were decreased to 85, 63 and
32%, respectively (Pant et al., 2012). Shoot growth in
hydroponically grown P. aureus seedlings was reduced at
40/30 and 45/35 °C by 18% and 34%, respectively. Root
growth at those temperatures was reduced by 13% and
23%, respectively (Kumar et al., 2011). Heat stresses sig-
nificanty altered photosynthesis, reproductive
development and yield. Glycine max exposed to HT stress
(38/28 °C, day/night) for 14 days during the flowering
stage showed a 20% decrease in photosynthesis and
16% decrease in stomatal conductance; a decreased
total chl content (18%), chl a content (7%) and chl a / b
ratio (3%); increased thickness of the palisade and

11.3.4 high temperature (ht)
One of the predicted negative effects of global warming
on plants is the damage due to HT on plant growth,
development and yield. The ever-increasing threat of
climate change including very HT might lead to cata-
strophic declines in crop productivity and result in