Agriculture Reference
In-Depth Information
occurred from flooding at the pod fill reproductive
stage - 20-39% less compared to non-flooded checks
(Rhine
et al.,
2010). Flooding stress significantly reduced
photosynthetic rate and leaf water potential in mung
bean. This stress also damaged lateral roots, to which
the plant responded by forming numerous adventitious
roots (Islam
et al.,
2010). Nodulation of legumes is an
important factor that is affected by flooding. Upon
waterlogging, the roots have no regular root hairs and
the water-stressed legumes develop numerous lateral
roots. The bases of these lateral roots form abundant
nodules, as observed in
Sesbania rostrata
(Capoen
et al.,
2010). Waterlogging (for 4 and 6 days) is also respon-
sible for oxidative stress in the pigeon pea (
C. cajan
)
cultivars ICP 301 (tolerant) and Pusa 207 (susceptible),
as indicated by generation of O
2
•
−
and H
2
O
2
. Oxidative
stress decreased the membrane stability index in roots
and leaves, and increased thiobarbituric acid-reactive
substances (TBRS) over control plants. Injury indices
were higher in the susceptible cultivar. With increased
oxidative stress, the activities of antioxidant enzymes
were also increased, such as SOD, APX, GR and CAT.
These were higher in ICP 301, and were correlated with
lower oxidative damage and enhanced tolerance com-
pared to Pusa 207 (Kumutha
et al.,
2009). Waterlogging
stress (3 and 7 days) in soybean resulted in increased
lipid peroxidation and H
2
O
2
levels in roots. Besides
these, some proteins have been identified in stressed
plants that are anaerobically induced, waterlogging-
responsive proteins; these serve for signal transduction,
programmed cell death, RNA processing, redox homeo-
stasis and metabolism of energy (Alam
et al.,
2010). A
gradual increase in water levels exacerbated defoliation
in
Lotus tenuis
. Flooding consistently increased plant
height, probably as a response to cope with flood condi-
tions at the expense of food reserves (Striker
et al.,
2011).
exposure to O
3
. Reducing sugars, non-reducing sugars,
total sugars, fats, total protein and dissolved protein all
decreased due to O
3
exposure. The decreases were
greater with higher O
3
concentrations, and
V. faba
L. was
more sensitive to ozone than
P. sativum
L. (Almohisen &
Alyemani, 2013). Ozone enters through stomata of
leaves and is rapidly broken down into different ROS,
which cause oxidative damage (Yan
et al.,
2010). Studies
of the effect of O
3
on 38 different accessions of the
model legume,
M. truncatula
, proved that O
3
causes sub-
stantial physiological disorder including modification of
antioxidant defence systems. Low stomatal conductance
and reduced transpiration rate were characteristic fea-
tures of O
3
stress, and increased ROS production and
lipid peroxidation were evident. Ozone increased the
levels of reduced ascorbate and total ascorbate, total
GSH and reduced GSH; this stress also significantly
raised the concentrations of oxidized forms of ascorbate
and glutathione (Puckette
et al.,
2007). Ozone fumiga-
tion of
Trifolium pratense
and
T. repens
leaves induced
elevated oxidative stress with a decrease of total gluta-
thione content, mainly due to the strong increase in
glutathione disulphide (GSSG) and decrease in GSH
(Scebba
et al.,
2003).
11.3.8 Ultraviolet radiation
Solar UV-B irradiance has increased due to stratospheric
ozone depletion, which has impacted adversely on living
organisms including plants. Most research has shown
that higher intensities and longer duration of UV radia-
tion are harmful for legumes, whereas some research
findings also showed that low-intensity, short-duration
exposure to UV radiation might have some benefits.
Natural levels of UV-B radiation (UV-B: 280-315 nm)
reduced soybean growth and yield, which was correlated
with CAT and APX activity and epidermal transmittance
(Mazza
et al.,
2013). Exposure to enhanced levels of
UV-B decreased total biomass accumulation, harvest
index, root:shoot ratio and yield in
V. radiata
L. cultivars,
and
Malviya janpriya
was more responsive to UV-B than
M. jyoti
(Agrawal
et al.,
2006). The impact of UV-B radia-
tion (UV-B: 280 to ~320 nm) on growth and biochemical
and antioxidant enzyme activity was studied in seedlings
of the green manure plant
Indigofera tinctoria
L. UV-B
radiation for 4 to 8 days significantly reduced leaf area,
shoot length, and fresh and dry weight of seedlings. It
decreased chl and carotenoid contents but increased
flavonoid and anthocyanin contents. These seedlings
11.3.7 Ozone
Tropospheric O
3
is a major threat to crop productivity
and forest ecosystems (Heagle, 1989). It can also be gen-
erated from anthropogenic activity like fossil fuel
combustion and biomass burning, and from biogenic
emissions (Kesselmeier & Staudt, 1999), and is formed
by photochemical oxidation of primary pollutants
such as N oxides, hydrocarbons and carbon monoxide
(Lelieveld & Crutzen, 1990). Ozone is responsible for
various injuries in plants. Leaf chlorosis, necrosis and
mottling were observed in
V. faba
and
P. sativum
L. upon
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