Environmental Engineering Reference
In-Depth Information
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 non-
assimilative processes consuming O
2
(photorespiration, Mehler reaction and chlo-
rorespiration) 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 activ-
ity 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
•
−
•
) (Mittler
2002
).
Oxidative stress occurs in any plant cell when there is an imbalance between produc-
tion 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 sensi-
tive 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 photo-
synthesis by high-temperature stress, driven by high irradiance or drought or heat stress,
is similar to that of high irradiance as mentioned earlier.
, and HO
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
