Agriculture Reference
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oxygen species or by decreasing the O
2
radical scavenging ability in the cell [176]. The drastic
increase in lipid peroxidation due to HT stress was reported by many researchers [162, 177].
Several lines of study indicated that under heat-stress conditions, malondialdehyde (MDA), a
product of peroxidation of unsaturated fatty acids, has been used as a good indicator of free
radical damage to cell membranes [12, 178, 179]. In wheat seedlings (8-d old) gradual increase
in the accumulation of H
2
O
2
was observed (0.5, 0.58, 0.78 and 1.1 μmol g
-1
FW) in response to
differential heat shock treatment of 22, 30, 35 and 40°C for 2 h [180]. The effect of a long-term
(24 h) HT (42°C) shock on oxidative damages in
T. aestivum
seedlings was investigated by
Savicka and Škute [181] in respect of the changes in O
2
●-
production and MDA content. The
effect of HT was analyzed at the early (4-d-old) and late stages (7-d-old) of seedling develop‐
ment. The increase of O
2
●-
production, which was observed in the first leaf of wheat seedlings
at all stages of development, led to an increase of MDA concentration. Parameter changes in
the level of O
2
●-
production were observed in the roots of wheat seedlings grown under HT
exposure for 24 h at all stages of development, but MDA concentration in the roots of experi‐
mental and control seedlings did not differ significantly at the early and late stages of devel‐
opment. The level of O
2
●-
production in coleoptile cells increased after a HT exposure at the
late stages of seedling development. They concluded that growth inhibition of the root system
could be connected with a powerful oxidative stress, evidenced by a significant increase (68%)
of O
2
●-
production in root cells during the early stages of seedling development and an
insignificant increase (6%) of O
2
●-
production 2 d after a HT exposure, as compared to control
seedlings. The increase of O
2
●-
production was also observed in roots after a HT stress during
the late stages of development, and this effect was present 2d after a HT exposure (6 and 42%,
respectively). Moreover, O
2
●-
production after 2d at the late stages was more intensive than at
the early stages of development (79% and 22%, respectively). In contrast, in the first leaf cells
at late seedling development stages a higher level of O
2
●-
production was observed immedi‐
ately after exposure (65%) as compared to 2 d after HT exposure (34%). The MDA content
increased by 27% in the first leaf in 2 d after exposure at the early stages of seedling develop‐
ment, and this trend also continued during the late stages of development (58%) [181]. Kumar
et al. [182] observed that high temperature of 40/35°C (day/night temperature) resulted in 1.8-
fold increase of MDA content in rice genotypes and 1.2- to 1.3-fold increase in maize genotypes
over the control treatment. At 45/40°C, a further increase of MDA content was observed in
both the crops, which were 2.2- to 2.4-fold increase in rice and 1.7-fold in maize genotypes
compared to control. Similarly at 40/35°C the H
2
O
2
level showed 1.9- to 2.0-fold elevation in
rice genotypes and 1.4- to 1.6-fold elevation in maize genotypes relative to their respective
controls. Moreover, at 45/40°C, H
2
O
2
content increased further in higher rate in maize geno‐
types.
Low temperature is also responsible for the production of ROS in plant cell [183, 184]. In
extreme cold beyond the plants tolerant level or in chilling sensitive plants the activities of
antioxidant enzymes are reduced which accelerate the accumulation of ROS in higher amount.
Production of ROS severely affects electron transfer and biochemical reactions [12, 108]. Low
temperature-induced oxidative stress decreases phospholipid content, increases lipid peroxi‐
dation, free and saturated fatty acid content [185-187]. This stress damages lipid, protein,
carbohydrate and DNA [Gill SS and Tuteja 2010], thus it alters the enzyme activities, bio‐
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