Photosynthesis in Nature: A New Look - Photobiogeochemistry of Organic Matter - page 593

Enhanced solar UV-A (315-400 nm) and/or UV-B radiation (280-315 nm)
can reduce growth and photosynthetic rates, inhibit pigment production, increase
permeability of cell membranes, damage proteins or DNA molecules, and even
lead to cell death (see chapter “ Impacts of Global Warming on Biogeochemical
Cycles in Natural Waters ” for more references) (Jiang and Qiu 2011 ). At nor-
mal ozone concentrations (i.e. 344 Dobson Units), UV radiation can reduce pri-
mary productivity in surface waters by as much as 50 % (see chapter “ Impacts
of Global Warming on Biogeochemical Cycles in Natural Waters ” for more ref-
erences) (Cullen and Neale 1994 ). A normal level of UV radiation also reduces
phytoplankton production by 57 % at a depth of 1 m, while such inhibition
decreases to <5 % at 30 m, at 50ºS in mid December (Arrigo 1994 ). Such effects
on aquatic organisms might be caused directly by UV radiation and indirectly
through high production of HO

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in epilimnetic (upper layer) waters. Both effects
are able to alter the structural configuration of organisms with release of many
organic substances in epilimnetic (surface layer) waters (see chapter “ Impacts of
Global Warming on Biogeochemical Cycles in Natural Waters ” for more refer-
ences) (Mostofa et al. 2009 ; Mostofa et al. 2009 ; Rastogi et al. 2010 ; Ingalls et
al. 2010 ). Some studies also hypothesize that the primary target of photodamage
to PSII by strong light is the PSII reaction center. A primary event in photoinhibi-
tion could be the damage to the D1 protein, which activates its rapid degradation
by several proteases (Aro et al. 1993 ; Andersson and Aro 2001 ; Nishiyama et al.
2008 ; Kanervo et al. 1993 ; Tyystjärvi et al. 2001 ). Studies show that hydroper-
oxides (H 2 O 2 and organic peroxides, ROOH) are often considered as indicators
of membrane damage (see also chapter “ Photoinduced and Microbial Generation
of Hydrogen Peroxide and Organic Peroxides in Natural Waters ” ) (Hagege et al.
1990a , b ).

Effects of Sunlight on Higher Plants

High irradiance can affect the PSII activity, with negative effect on the PSII-
mediated electron transport rate, disarrangement of PSII system, degradation of
the D1 protein and/or its metabolism in a circadian-dependent manner (the same
issue could also involve various polypeptides) (Aro et al. 1993 ; Pandey and Yeo
2008 ; Maslenkova et al. 1995 ; Rintamäki et al. 1995 ; Baena-González and Aro
2002 ; Booij-James et al. 2002 ; Hofman et al. 2002 ; Henmi et al. 2003 , 2004 ;
Nováková et al. 2004 ; Porta et al. 2004 ; Suzuki et al. 2004 ; Szilárd et al. 2007 ).
The final result is a decrease of the photosynthetic capacity of plants. The decrease
in photosynthetic efficiency is mostly associated with three facts: First, the decline
in the enzymatic reactions of the Calvin-Benson cycle (Friedrich and Huffaker
1980 ); second, the decrease in the light reactions, i.e. the photoinduced reac-
tions of PSI and PSII (Grover and Mohanty 1992 ; Wingler et al. 2004 ); and third,
the changes in the structure of chloroplasts (Tang et al. 2005 ). UV-B sensitivity
depends on the oxidation state of the water-splitting complex of PS II in higher
plant such as spinach (Szilárd et al. 2007 ). It has been shown that ROS produced
endogeneously under high-irradiance conditions can cause more deleterious effect