610
K. M. G. Mostofa et al.
high-temperature episodes when leaf temperature can exceed the air temperature
by as much as 15 °C (Singsaas and Sharkey 1998; Hanson et al. 1999; Singsaas et
al. 1999). Rubisco can produce hydrogen peroxide as a result of oxygenase side
reactions, which can increase substantially with temperature (Sharkey 2005).
Moreover, an increase in temperature can induce sinks of electron transport
different from CO 2 assimilation, and photorespiration is increased at 30–35 °C
(D’Ambrosio et al. 2006). The O 2 -independent electron transport can account for up
to 20 % of the total PSII electron transport in wild watermelon leaves (Miyake and
Yokota 2000, 2001). The electron flux in PSII that exceeds the flux required for the
cycles of photosynthetic carbon reduction and photorespiratory carbon oxidation,
can induce photoreduction of O 2 in the water–water cycle (Miyake and Yokota 2000,
2001). It has been shown that the greater partitioning of reductive power to nonassimilative processes consuming O 2 (photorespiration, Mehler reaction and chlororespiration) with respect to CO 2 assimilation allows keeping the PSII efficiency
factor unmodified at temperatures as high as 35 °C (D’Ambrosio et al. 2006).
The unsaturation of fatty acids can protect PSII from the inhibition of the activity that is caused by strong light at low temperatures (Wada et al. 1990; Murata
et al. 1992), and can accelerate the repair of photodamaged PSII (Gombos
et al. 1994; Wada et al. 1994; Moon et al. 1995). After photodamage to PSII in
Synechocystis at low temperatures (0–10 °C), activity recovery can reach up to
50 % of the original level in the darkness at moderate temperatures, without the de
novo synthesis of D1 protein (Nishiyama et al. 2008).
High-temperature stress can disrupt the cellular metabolic homeostasis and promote
the production of reactive oxygen species (H 2 O 2 , 1 O 2 , O 2
•−
, and HO
•
) (Mittler 2002).
Oxidative stress occurs in any plant cell when there is an imbalance between production of ROS and antioxidant defense (Apel and Hirt 2004; Mittler 2002; Scandalios
2002). The consequence is a decrease of the net photosynthetic efficiency that affects
various plant activities (Ogweno et al. 2008; Apel and Hirt 2004; García-Ferris and
Moreno 1994; Alscher et al. 1997; Anderson 2002; Irihimovitch and Shapira 2000;
Pfannschmidt 2003). Calvin-cycle enzymes within chloroplasts are particularly sensitive to high levels of H 2 O 2 , which decreases CO 2 fixation and foliar biomass (Willekens
et al. 1997; Zhou et al. 2004, 2006). The mechanism behind the decline of plant photosynthesis by high-temperature stress, driven by high irradiance or drought or heat stress,
is similar to that of high irradiance as mentioned earlier.
5.4 Effects of Water Stress (Drought)
and of Precipitation/Rainfall
Water stress or drought stress can significantly affect plant photosynthesis and
decrease their growth, development and productivity (Li and van Staden 1998;
Hassan 2006; Liu et al. 2006; Ohashi et al. 2006; Fariduddin et al. 2009). Water
or drought stress can stimulate changes in water balance, leaf area expansion,
absorption of photosynthetically active radiation, stomatal closure that reduces
K. M. G. Mostofa et al.
high-temperature episodes when leaf temperature can exceed the air temperature
by as much as 15 °C (Singsaas and Sharkey 1998; Hanson et al. 1999; Singsaas et
al. 1999). Rubisco can produce hydrogen peroxide as a result of oxygenase side
reactions, which can increase substantially with temperature (Sharkey 2005).
Moreover, an increase in temperature can induce sinks of electron transport
different from CO 2 assimilation, and photorespiration is increased at 30–35 °C
(D’Ambrosio et al. 2006). The O 2 -independent electron transport can account for up
to 20 % of the total PSII electron transport in wild watermelon leaves (Miyake and
Yokota 2000, 2001). The electron flux in PSII that exceeds the flux required for the
cycles of photosynthetic carbon reduction and photorespiratory carbon oxidation,
can induce photoreduction of O 2 in the water–water cycle (Miyake and Yokota 2000,
2001). It has been shown that the greater partitioning of reductive power to nonassimilative processes consuming O 2 (photorespiration, Mehler reaction and chlororespiration) with respect to CO 2 assimilation allows keeping the PSII efficiency
factor unmodified at temperatures as high as 35 °C (D’Ambrosio et al. 2006).
The unsaturation of fatty acids can protect PSII from the inhibition of the activity that is caused by strong light at low temperatures (Wada et al. 1990; Murata
et al. 1992), and can accelerate the repair of photodamaged PSII (Gombos
et al. 1994; Wada et al. 1994; Moon et al. 1995). After photodamage to PSII in
Synechocystis at low temperatures (0–10 °C), activity recovery can reach up to
50 % of the original level in the darkness at moderate temperatures, without the de
novo synthesis of D1 protein (Nishiyama et al. 2008).
High-temperature stress can disrupt the cellular metabolic homeostasis and promote
the production of reactive oxygen species (H 2 O 2 , 1 O 2 , O 2
•−
, and HO
•
) (Mittler 2002).
Oxidative stress occurs in any plant cell when there is an imbalance between production of ROS and antioxidant defense (Apel and Hirt 2004; Mittler 2002; Scandalios
2002). The consequence is a decrease of the net photosynthetic efficiency that affects
various plant activities (Ogweno et al. 2008; Apel and Hirt 2004; García-Ferris and
Moreno 1994; Alscher et al. 1997; Anderson 2002; Irihimovitch and Shapira 2000;
Pfannschmidt 2003). Calvin-cycle enzymes within chloroplasts are particularly sensitive to high levels of H 2 O 2 , which decreases CO 2 fixation and foliar biomass (Willekens
et al. 1997; Zhou et al. 2004, 2006). The mechanism behind the decline of plant photosynthesis by high-temperature stress, driven by high irradiance or drought or heat stress,
is similar to that of high irradiance as mentioned earlier.
5.4 Effects of Water Stress (Drought)
and of Precipitation/Rainfall
Water stress or drought stress can significantly affect plant photosynthesis and
decrease their growth, development and productivity (Li and van Staden 1998;
Hassan 2006; Liu et al. 2006; Ohashi et al. 2006; Fariduddin et al. 2009). Water
or drought stress can stimulate changes in water balance, leaf area expansion,
absorption of photosynthetically active radiation, stomatal closure that reduces