Extreme Temperature Responses, Oxidative Stress and Antioxidant Defense in Plants - Abiotic Stress: Plant Responses and Applications in Agriculture - page 189

flavonoids, and phenolic compound of seedlings subjected to LT stress which was mainly due
to the ability to scavenge ROS. They showed a significant increase in activities of POD and
CAT in Se treated wheat seedlings under LT. Liu et al. [198] found insufficient antioxidant
defense in Cucumis sativus seedlings under chilling (4°C). But when the seedlings were
pretreated with 1.0 mM SNP (NO donor) and exposed to LT they observed that treatment with
NO donor stimulated the activities of various enzymes such as SOD, GR, POD and CAT which
indicates that exogenous NO enhanced chilling stress tolerance. It was also observed that due
to SNP treatment the MDA content was significantly decreased (27%) in chilling-stressed
seedlings as compared to stress alone. Yang et al. [199] observed that the enhanced activities
of SOD, CAT, APX and POX in C. sativus plants reflected better tolerance to chilling. The
activities of SOD, APX, GR and POX increased in cold-acclimated Cicer arietinum plants at the
chilling stress of 2 and 4°C which enhanced their chilling tolerance [200].
7. Conclusion and future perspectives
The extreme temperatures those are consequences of present-day global climate changes are
considered as major abiotic stresses for crop plants. Different plant studies clearly show that
temperatures exceeding the limits of adaptation substantially influence the metabolism, viabil‐
ity, physiology, and yield of many plants. Plants exposed to extreme temperatures often show
a common response in the form of oxidative stress. However, the extent of damage caused by
extreme temperatures depends greatly on the duration of the adverse temperature, the geno‐
types of the exposed plants, and their stage of growth. There is ample need to develop tempera‐
ture tolerance in crop plants by exploring suitable strategies. Numerous research findings
support the notion that induction and regulation of antioxidant defenses are necessary for ob‐
taining substantial tolerance against environmental stress. The development of genetically en‐
gineered plants, by the introduction and/or overexpression of selected genes, would to be one
feasible strategy. However, plant adaptation to either HT or LT is a multigenic response which
is very complex in nature. Thus the task of identifying the traits those correlate with stress toler‐
ance is incredibly difficult for researchers.
At present, number of genes have been identified in different studies but the knowledge of the
transcriptional control of extreme temperature responses is limited. In addition, the regulation
of these transcriptional responses is far more complex than previously believed. In recent
years, a number of exogenous protectants, such as proline, glycinebetaine, nitric oxide, silicon,
selenium, salicylic acid, and polyamines have been tested and found to be beneficial in protect‐
ing plants against damage from temperature extremes. Therefore, more advanced research
should conduct focusing on the development of plants those restrain genes which promote the
accumulation/synthesis of these beneficial elements and compounds. Considering these facts,
a well organized approach should combine to investigate the molecular, physiological, and
metabolic aspects of temperature stress tolerance both at the cellular and the whole plant level.