reducing the acceptance of light quanta, avoiding excessive free radicals, and
causing damage to plants (Havaux and Tardy 1999). To identify the tolerant line,
the increased affinity of Rubisco for CO 2 versus oxygen, and a better catalytic rate in
photosynthesis are likely to be key targets beneficial at warmer temperatures (Parry
et al. 2011).
3.2.2.3 Water Relations
In field conditions deficit of soil water and HT occur simultaneously hindrance the
growth and physiological process of the plant in tropical and sub-tropical
environments (Wahid et al. 2007; De Boeck et al. 2015; Zandalinas et al. 2016).
The stable tissue water status was found to be severely impaired under HS with
limited soil water (Nicolas et al. 1984; Machado and Paulsen 2001) leads to a
reduction of osmotic potential in leaf (Huve et al. 2005). Increased water use
efficiency (net CO 2 assimilation rate/transpiration) causes stomatal closure with a
reduction in the net photosynthetic rate (Ruggiero et al. 2017). In wheat, under stress
condition increase in the leaf temperature resulted in a decrease in the relative water
content, water potential in leaves, and reduction in photosynthetic productivity
affecting the rate of transpiration and plant growth (Feng et al. 2014). Hussain
et al. (2019) observed that under HS stomatal conductance and transpiration rate
in maize leaves increased with high water losses. Water and nutrient availability
aboveground parts of the plant depended upon the turgor pressure within cells and
other components such as root number, mass, and growth of the roots (Wahid et al.
2007; Huang et al. 2012). HT increases evaporation in younger plants especially
under the shorter period of heat stress to cool the tissue, depending upon the
availability of water in soil (Balla et al. 2019). Sharma et al. 2015 reported that
stomatal conductance decreases with increase in temperature and transpiration was
increase while Balla et al. 2019 reported that out of total genotypes studied only a
few showed the same reaction type and clearly understood that no strong alliance
exists among stomatal conductance, evaporation and heat stress tolerance. The
reproductive stage is highly susceptible to water stress and is more difficult with a
gradual increase in temperature. To maintain an upper limit of water status during
flowering the optimum temperature should not increase above 31
C (Atkinson and
Urwin 2012). Almeselmani et al. (2009) in wheat, noticed that HT (35/25
C) inflicts
after the tillering stage resulted in decline in water potential and is more severe in
susceptible genotypes to HS. The HT in plant increases the transpiration and
reduction of the osmotic potential in leaf resulted in the release of several
antioxidants linked to dehydration tolerance (Ahmad et al. 2010). HT seems to
cause a rise in hydraulic conductivity to facilitate the aquaporin activity in the
plant cell membrane (Martinez-Ballesta et al. 2009) and reduced water viscosity
(Cochard et al. 2007). In heat-tolerant durum and bread wheat genotypes, maintenance of high stomatal conductance is a prerequisite to promote transpiration for heat
dissipation (Dias et al. 2008).
3 Plant Morphological, Physiological Traits Associated with Adaptation Against. . .
59
causing damage to plants (Havaux and Tardy 1999). To identify the tolerant line,
the increased affinity of Rubisco for CO 2 versus oxygen, and a better catalytic rate in
photosynthesis are likely to be key targets beneficial at warmer temperatures (Parry
et al. 2011).
3.2.2.3 Water Relations
In field conditions deficit of soil water and HT occur simultaneously hindrance the
growth and physiological process of the plant in tropical and sub-tropical
environments (Wahid et al. 2007; De Boeck et al. 2015; Zandalinas et al. 2016).
The stable tissue water status was found to be severely impaired under HS with
limited soil water (Nicolas et al. 1984; Machado and Paulsen 2001) leads to a
reduction of osmotic potential in leaf (Huve et al. 2005). Increased water use
efficiency (net CO 2 assimilation rate/transpiration) causes stomatal closure with a
reduction in the net photosynthetic rate (Ruggiero et al. 2017). In wheat, under stress
condition increase in the leaf temperature resulted in a decrease in the relative water
content, water potential in leaves, and reduction in photosynthetic productivity
affecting the rate of transpiration and plant growth (Feng et al. 2014). Hussain
et al. (2019) observed that under HS stomatal conductance and transpiration rate
in maize leaves increased with high water losses. Water and nutrient availability
aboveground parts of the plant depended upon the turgor pressure within cells and
other components such as root number, mass, and growth of the roots (Wahid et al.
2007; Huang et al. 2012). HT increases evaporation in younger plants especially
under the shorter period of heat stress to cool the tissue, depending upon the
availability of water in soil (Balla et al. 2019). Sharma et al. 2015 reported that
stomatal conductance decreases with increase in temperature and transpiration was
increase while Balla et al. 2019 reported that out of total genotypes studied only a
few showed the same reaction type and clearly understood that no strong alliance
exists among stomatal conductance, evaporation and heat stress tolerance. The
reproductive stage is highly susceptible to water stress and is more difficult with a
gradual increase in temperature. To maintain an upper limit of water status during
flowering the optimum temperature should not increase above 31
C (Atkinson and
Urwin 2012). Almeselmani et al. (2009) in wheat, noticed that HT (35/25
C) inflicts
after the tillering stage resulted in decline in water potential and is more severe in
susceptible genotypes to HS. The HT in plant increases the transpiration and
reduction of the osmotic potential in leaf resulted in the release of several
antioxidants linked to dehydration tolerance (Ahmad et al. 2010). HT seems to
cause a rise in hydraulic conductivity to facilitate the aquaporin activity in the
plant cell membrane (Martinez-Ballesta et al. 2009) and reduced water viscosity
(Cochard et al. 2007). In heat-tolerant durum and bread wheat genotypes, maintenance of high stomatal conductance is a prerequisite to promote transpiration for heat
dissipation (Dias et al. 2008).
3 Plant Morphological, Physiological Traits Associated with Adaptation Against. . .
59