3.2.2.2 Photosynthesis and Photosystems
Photosynthesis, one of the most sentient physiological processes, which is adversely
affected at supra-optimal temperatures in wheat (Dias et al. 2010; Feng et al. 2014).
The optimum temperature range for photosynthetic processes in most of the crop
species is 30
C to 35
C, however, as the temperature reaches to >40
C, it
influences on the photosynthetic capacity of plants especially of C3 plants (wheat)
than C4 plants like maize (Berry and Bjorkman 1980; Schuster and Monson 1990;
Crafts-Brandner and Salvucci 2002; Naidu et al. 2003; Shah and Paulsen 2003;
Cheikh and Jones 2006; Yang et al. 2006; Massad et al. 2007; Tao et al. 2016). There
is a sharp decline in photosynthetic rates in wheat and maize crops when exposed to
HS in both the vegetative and reproductive phases. Al-Khatib and Paulsen (1984)
and Grover et al. (1986) observed that failure in the supply of photosynthates during
grain filling stage conducive to reduce grain yield and biomass (Edreira and Otegui
2012) and it is more prone at night HT (>14
C) in wheat (Prasad et al. 2008a) and
maize (Crafts-Brandner and Salvucci 2002). The rise in photosynthesis rate during
the post-anthesis stage resulted in increases in grain filling (Martinez et al. 2014).
Fan et al. (2015) in wheat, illustrated that warmer temperature in the night at postanthesis stage in winter increased the flag leaf photosynthetic carbon assimilation
ability resulting in the accumulation of photosynthetic products, confirmed by the
relatively high content of Rubisco (ribulose1,5-bisphosphate carboxylase) and soluble protein at the post-anthesis stage, which was conducive to increase grain yield.
HS impairs the process of photosynthesis comprises various components, including
the photosystems (Camejo et al. 2005), photosynthetic pigments (Camejo et al.
2006), and CO 2 reduction pathways (Wise et al. 2004).
Damage and disorder caused by HS in the stroma and thylakoid lamellae of
chloroplast inhibit the activities of membrane-associated electron carriers and
enzymes, and cessation of photophosphorylation (Wise et al. 2004; Marchand
et al. 2005; Ristic et al. 2008; Wang et al. 2009, 2010). HT leads to swelling,
increased leakiness, and disruption of all photochemical reactions especially from
light-harvesting complex II from the photosystem (PS) II core complex, and disintegration of PS II-mediated electron transfer of thylakoid (Ristic et al. 2008; Marutani
et al. 2012) and thus, impairment of thylakoids caused chlorophyll loss (Ristic et al.
2007, 2008). At HT dissociation of Rubisco activase enzyme (Prasad et al. 2004;
Ahmad et al. 2010) resulted in a reduction of the photosynthetic capacity in both
light and dark conditions but it is irreversible under the dark condition in wheat
(Mathur et al. 2011; Raines 2011). Thus, suppression of carbon assimilation resulted
in a reduction of ROS generation (Camejo et al. 2006; Guo et al. 2009) in response,
reduction in protein synthesis and prevent recovery of impaired PS II (Murata et al.
2007; Allakhverdiev et al. 2008). At very high level, it may result in severe cell
injury and even cell death (Apel and Hirt 2004). Amirjani (2012) reported that in the
case of the wheat crop, the amount of chlorophyll (Chl) a, Chl b, and carotenoids did
not significantly change at control condition (30/25
C), but reduced at HT
(35/30
C), while the Chl a/b and Chlorophyll to carotenoids ratios remained
unaltered under HS. In maize, HS promotes the degradation of chlorophyll affects
the contents of Chl a, Chl b, and total Chl (Hussain et al. 2019), and resulted in
58
R. Gajghate et al.
Photosynthesis, one of the most sentient physiological processes, which is adversely
affected at supra-optimal temperatures in wheat (Dias et al. 2010; Feng et al. 2014).
The optimum temperature range for photosynthetic processes in most of the crop
species is 30
C to 35
C, however, as the temperature reaches to >40
C, it
influences on the photosynthetic capacity of plants especially of C3 plants (wheat)
than C4 plants like maize (Berry and Bjorkman 1980; Schuster and Monson 1990;
Crafts-Brandner and Salvucci 2002; Naidu et al. 2003; Shah and Paulsen 2003;
Cheikh and Jones 2006; Yang et al. 2006; Massad et al. 2007; Tao et al. 2016). There
is a sharp decline in photosynthetic rates in wheat and maize crops when exposed to
HS in both the vegetative and reproductive phases. Al-Khatib and Paulsen (1984)
and Grover et al. (1986) observed that failure in the supply of photosynthates during
grain filling stage conducive to reduce grain yield and biomass (Edreira and Otegui
2012) and it is more prone at night HT (>14
C) in wheat (Prasad et al. 2008a) and
maize (Crafts-Brandner and Salvucci 2002). The rise in photosynthesis rate during
the post-anthesis stage resulted in increases in grain filling (Martinez et al. 2014).
Fan et al. (2015) in wheat, illustrated that warmer temperature in the night at postanthesis stage in winter increased the flag leaf photosynthetic carbon assimilation
ability resulting in the accumulation of photosynthetic products, confirmed by the
relatively high content of Rubisco (ribulose1,5-bisphosphate carboxylase) and soluble protein at the post-anthesis stage, which was conducive to increase grain yield.
HS impairs the process of photosynthesis comprises various components, including
the photosystems (Camejo et al. 2005), photosynthetic pigments (Camejo et al.
2006), and CO 2 reduction pathways (Wise et al. 2004).
Damage and disorder caused by HS in the stroma and thylakoid lamellae of
chloroplast inhibit the activities of membrane-associated electron carriers and
enzymes, and cessation of photophosphorylation (Wise et al. 2004; Marchand
et al. 2005; Ristic et al. 2008; Wang et al. 2009, 2010). HT leads to swelling,
increased leakiness, and disruption of all photochemical reactions especially from
light-harvesting complex II from the photosystem (PS) II core complex, and disintegration of PS II-mediated electron transfer of thylakoid (Ristic et al. 2008; Marutani
et al. 2012) and thus, impairment of thylakoids caused chlorophyll loss (Ristic et al.
2007, 2008). At HT dissociation of Rubisco activase enzyme (Prasad et al. 2004;
Ahmad et al. 2010) resulted in a reduction of the photosynthetic capacity in both
light and dark conditions but it is irreversible under the dark condition in wheat
(Mathur et al. 2011; Raines 2011). Thus, suppression of carbon assimilation resulted
in a reduction of ROS generation (Camejo et al. 2006; Guo et al. 2009) in response,
reduction in protein synthesis and prevent recovery of impaired PS II (Murata et al.
2007; Allakhverdiev et al. 2008). At very high level, it may result in severe cell
injury and even cell death (Apel and Hirt 2004). Amirjani (2012) reported that in the
case of the wheat crop, the amount of chlorophyll (Chl) a, Chl b, and carotenoids did
not significantly change at control condition (30/25
C), but reduced at HT
(35/30
C), while the Chl a/b and Chlorophyll to carotenoids ratios remained
unaltered under HS. In maize, HS promotes the degradation of chlorophyll affects
the contents of Chl a, Chl b, and total Chl (Hussain et al. 2019), and resulted in
58
R. Gajghate et al.