Introduction
High temperature is one of the most important constraints
for wheat growth and development, decreasing yield by
3–5 % per 1 C rise in temperature (Gibson and Paulsen
1999). According to a report of intergovernmental panel on
climate change (IPCC), global mean temperature is rising
at 0.3 C per decade reaching to approx 1 and 3 C above
the present value by years 2025 and 2100, respectively, and
thus leading to global warming (Jones et al. 1999). Plant
responses to high temperatures are mediated by both their
inherent ability to survive (basal tolerance) and their ability
to acquire tolerance to otherwise lethal temperatures
(acclimation). These two mechanisms in cereals are due to
the activation of different genetic systems (Maestri et al.
2002). Direct injuries due to high temperature include
protein denaturation, aggregation and increased fluidity of
membrane lipids. Indirect or slower heat injuries include
inactivation of enzymes in chloroplast and mitochondria,inhibition of protein synthesis, protein degradation and loss
of membrane integrity (Wahid 2007).