Extreme Temperature Responses, Oxidative Stress and Antioxidant Defense in Plants - Abiotic Stress: Plant Responses and Applications in Agriculture - page 187

chemical reactions and plant physiological processes including photosynthesis, respiration,
nutrient movements, transpiration which negatively affect plants survival. In extreme cases
ROS induced oxidative stress causes cell death [160].
However, recent studies have shown that ROS could also play a key role in mediating
important signal transduction events. The rates of ROS production during temperature stress
could play a central role in stress perception and protection [12].
6. Antioxidant defense under temperature stress
Plants have various enzymatic and non-enzymatic defense systems to minimize the deleteri‐
ous effects of ROS which include the enzymes: catalase (CAT), ascorbate peroxidase (APX),
monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), gluta‐
thione reductase (GR), glutathione S -transferase (GST), glutathione peroxidase (GPX),
superoxide dismutase (SOD) etc. as well as non-enzymatic compounds such as ascorbate
(AsA), glutathione (GSH), carotenoids etc. However, under the extreme condition, ROS
production overwhelm the scavenging action of the antioxidant system, which results in
extensive cellular damage and death. In such cases external protectants as well as genetic
manipulation of defense genes can work in upregulating the defense system which is also true
for temperature stress induced oxidative damage. There are numerous plant studies which
indicate the tolerance to temperature stress in plants is positively correlated with an increase
in antioxidants [3, 17, 18, 188, 189].
Under HT stress, plants are found to accumulate enhanced amount of non-enzymatic antiox‐
idant and upregulate the activities of antioxidant enzymes. However, in most of the cases these
enhanced activities are not sufficient for stress tolerance in plants, especially in susceptible
genotypes [3, 18]. Almeselmani et al. [18] observed that the activities of SOD, APX, CAT, GR
and POX were increased significantly at all stages of growth in heat-tolerant cultivars (C 306)
in response to heat stress while the susceptible cultivar (PBW 343) showed a significant
reduction in CAT, GR and POX activities. While investigating the induction of antioxidant
enzymes (SOD, APX, GR and CAT) in wheat shoot under HT stresses, Badawi et al. [190]
observed that three wheat genotypes (Fang, Siete Cerros and Imam) showed differences in
their antioxidant enzyme activities. Importantly, Fang, the heat tolerant genotype, showed
higher SOD, APX, GR and CAT activities under HT stress compared to the other two genotypes
which indicated the role of the antioxidant defense system in conferring heat stress tolerance.
Djanaguiraman et al. [86] observed that HT stress decreased antioxidant enzyme activities and
increased oxidant production in sorghum. In their study, SOD, CAT and POX activities were
decreased in heat stress (22, 15 and 25% lower than control plants) and the greater inhibition
of all antioxidant enzymes in heat-stressed plants relative to control plants indicates greater
inactivation of all antioxidant enzymes by heat stress. On the other hand, the application of
selenium (Se) decreased oxidative damages by enhancing antioxidant defense resulting in
higher grain yield. In addition, the increase in antioxidant enzyme activities and decrease in
ROS content by Se was greater in HT than in optimum temperature. In Cicer arietinum plants,