Agriculture Reference
In-Depth Information
Rubisco activity was inhibited via Rubisco activase inhibition under mod-
erately high temperatures, 30 and 35 °C in cotton and wheat, respectively.
10.4.4.4
CELL MEMBRANE THERMO STABILITY
Cellular membranes play an important role for fundamental trends like
respiration and photosynthesis under heat stress (Blum, 1988). Heat stress
enhances the kinetic energy and motion of molecules in membranes lead
to loss of chemical bonds in molecules of biological membranes. This
causes the lipid bilayer of biological membranes to be rather liquid by
either proteins de naturation or a rise in fatty acids that are unsaturated
(Savchenko et al., 2002). The stability and roles of biological membranes
are susceptible to high temperature, as heat stress changes the tertiary and
quaternary structures of the membrane proteins. These changes increase
the penetrance of membranes, as obvious from increased loss of electro-
lytes. The enhanced solute leakage, as a symptom of diminished cell mem-
brane thermo stability (CMT), has long been applied as an indirect estima-
tion of heat-stress resistance in different crop species, involving potato
and tomato (Chen et al., 1982), soybean (Martineau et al., 1979), cotton
(Ashraf et al., 1994), cowpea (Ismail and Hall, 1999), wheat (Blum et al.,
2001), sorghum (Marcum, 1998), and barley (Wahid and Shabbir, 2005).
10.4.4.5
ALTERATIONS IN HORMONE
Crops have the capability to monitor and adjust to inappropriate environ-
mental situations, although the adaptability or tolerance degree to spe-
cial stresses varies between species and genotypes. The role of hormones
in this regard is imperative. Under heat stress condition, hormonal ho-
meostasis, stability, content, biosynthesis and compartmentalization are
changed (Maestri et al., 2002). Stress hormones such as abscissic acid
(ABA) and ethylene (C
2
H
4
), act as signal molecules and thus regulate vari-
ous physiological mechanisms. Diverse environmental stresses, such as
high temperature, leads to enhanced ABA levels (Larkindale and Huang,
2005). Induction of various HSPs (e.g., HSP70) by ABA can be another
mechanism of developing thermo resistance (Pareek et al., 1998). Another
hormone, brassinosteroidsis responsible for heat resistance in oilseed rape
(
Brassicanapus
) and tomato. Different hormonal factors are also related
