Photosynthesis in Nature: A New Look - Photobiogeochemistry of Organic Matter - page 606

under chilling condition (Powles 1984 ; Kudoh and Sonoike 2002 ; Bongi and Long
1987 ; Garstka et al. 2007 ). The decrease of the carotenoid content at lower tem-
peratures in B. vulgaris can enhance damage by ROS, because of the important
photoprotective function of carotenoids in scavenging highly destructive singlet
oxygen. Furthermore, they can prevent 1 O 2 formation by reacting with the chlo-
rophyll triplet state (Havaux et al. 1998 ). Low temperature stress can also enhance
photodamage to PS II under strong light (Wada et al. 1990 ; Murata et al. 1992 ;
Öquist et al. 1993 ; Öquist and Huner 1991 ), and repair of PS II under low-temper-
ature stress conditions is inhibited both in Synechocystis and plants (Gombos et al.
1994 ; Wada et al. 1994 ; Moon et al. 1995 ; Alia et al. 1998 ).
At higher temperature (>25 °C) caused by heat stress or drought stress, pho-
tosynthetic efficiency is significantly altered and can lead to decreased growth
and development of plants (D'Ambrosio et al. 2006 ; Pastenes and Horton 1996 ;
Pastenes and Horton 1996 ; Salvucci and Crafts-Brandner 2004 ; Sharkey 2005 ).
The effect of high temperature on organisms is expected to become more and
more significant. The global mean temperature has increased by 0.6 °C from
1990 to 2000 and is projected to increase by another 1.4 to over 5 °C by 2100
(see chapter “ Impacts of Global Warming on Biogeochemical Cycles in Natural
Waters ” for detailed description). Heat stress can induce several processes such
as: saturation of electron transport rate and disruption of its activity; decrease
of stomatal conductance; increase in increase in O 2 -consuming photorespira-
tion and non-photoinduced quenching; decreased affinity of the enzyme for CO 2 ;
decrease in CO 2 fixation; inactivation of the oxygen-evolving enzymes of PSII;
increase in the activity of antioxidant enzymes such as superoxide dismutase,
ascorbate peroxidase, guaiacol peroxidase, and catalase; decrease in PSII activ-
ity, and finally of photosynthetic capacity (Ogweno et al. 2008 ; D'Ambrosio
et al. 2006 ; Pastenes and Horton 1996 ; Pastenes and Horton 1996 ; Salvucci and
Crafts-Brandner 2004 ; Sharkey 2005 ; Schuster and Monson 1990 ; Heckathorn
et al. 2002 ; Mazorra et al. 2002 ; Barua et al. 2003 ; Núñez et al. 2003 ;
El-Shintinawy et al. 2004 ; Rivero et al. 2004 ; Cao et al. 2005 ).
Moderate heat stress can cause increased thylakoid proton conductance and
increased cyclic electron flow around PSI (Pastenes and Horton 1996 ; Bukhov
et al. 1999 , 2000 ; Bukhov and Carpentier 2000 ; Egorova and Bukhov 2002 ). PSI-
mediated cyclic electron flow can occur via either of two routes: the first is anti-
mycin A-sensitive and involves ferredoxin plastoquinone reductase; the second
one involves the NAD(P)H dehydrogenase complex (Bukhov et al. 2000 ; Thomas
et al. 1986 ; Boucher et al. 1990 ; Joët et al. 2001 ).
It has also been shown that high temperatures stress (often above 45 °C) can
damage PSII (Terzaghi et al. 1989 ; Thompson et al. 1989 ; Gombos et al. 1994 ;
Çjánek et al. 1998 ; Yamane et al. 1998 ). Furthermore, photorespiration increases
with increasing temperature, faster than photosynthesis (Schuster and Monson
1990 ). High leaf temperatures can reduce plant growth, and it is estimated that up
to 17 % decrease in crop yield can occur for each degree Celsius increase of aver-
age temperature during the growing season (Lobell and Asner 2003 ). Additionally,
leaves with low transpiration rates (e.g. oak leaves) can suffer frequent