579
Photosynthesis in Nature: A New Look
(Draper and Crosby 1981; Zepp et al. 1992; Wang et al. 2001; White et al. 2003;
Nakatani et al. 2007; Vione et al. 2006, 2009a, b).
3.6 Occurence of H 2 O 2 and its Effect on Photosynthesis
In support of the involvement of H 2 O 2 in the photosynthetic reaction, several
H 2 O 2 -related phenomena have been observed in natural waters, which can be classified as follows (Mostofa et al. 2009). First, the correlation between carbon production and photolytically formed H 2 O 2 concentration, suggesting a link between
hydrogen peroxide and organic matter photosynthesis in lake water (Anesio et al.
2005). Second, Chl a production in the epilimnetic layer (5–10 m) is typically
observed to increase with a decrease in total CO 2 contents (Talling 2006), suggesting that photosynthesis is highest at the epilimnetic layer (5–10 m) than in
the uppermost epilimnion (0–1 m). Correspondingly, the O 2 and Chl a contents
reach a minimum when the water temperature become highest during the summer
stratification period (Talling 2006), suggesting that photoinduced degradation or
assimilation of Chl a may be responsible for the decrease in Chl a at the uppermost layer. Here O 2 may be involved in the production of free radicals (H 2 O 2 or
HO
•
) that could inhibit photosynthesis (Mostofa and Sakugawa 2009; Moffett and
Zafiriou 1990). This result is similar to earlier studies where photosynthesis was
observed to be less effective in the uppermost layer (1 m) compared to the subsequent epilimnion (3 m) (Nozaki et al. 2002). A ratio of variable to maximal fluorescence (Fv/Fm) of phytoplankton productivity showed a decrease as irradiance
increased during the morning and an increase as irradiance declined in the afternoon. These results may be associated with both photoprotective strategies in the
antennae of PSII and photo damage of PSII reaction centers (Zhang et al. 2008).
Conversely, H 2 O 2 usually increases gradually starting in the morning, reaches a
maximum at noon and then gradually decreases in the afternoon (Mostofa and
Sakugawa 2009). It is therefore suggested that high production of H 2 O 2 and subsequent photoinduced generation of HO
• at noon is susceptible to damage the PSII
reaction centers.
Third, H 2 O 2 may be concentrated by particulate organic matter or small fungi
through rapid transpiration (Komissarov 1994, 1995, 2003). This hypothesis
can be supported by observation of relatively low production of H 2 O 2 in unfiltered samples compared to filtered ones during irradiation (Moffett and Zafiriou
1990; Cooper et al. 1988; Petasne and Zika 1997). An increase in the growth rate
of plants and mycelial fungi is detected when the H 2 O 2 concentration increases
up to an optimum level, from 1 nM to 10 M, and the growth rate decreases when
H 2 O 2 approaches 1 mM (Komissarov 2003; Ivanova et al. 2005). High levels of
H 2 O 2 may photolytically produce HO
•
, a strong oxidizing agent, that may cause
ecophysiological disorders in plants, decrease the CO 2 assimilation rate and
affect stomatal conductance, fluorescence and needle life span (Kume et al. 2000;
Kobayashi et al. 2002). In natural waters, HO
• that is produced photolytically from
Photosynthesis in Nature: A New Look
(Draper and Crosby 1981; Zepp et al. 1992; Wang et al. 2001; White et al. 2003;
Nakatani et al. 2007; Vione et al. 2006, 2009a, b).
3.6 Occurence of H 2 O 2 and its Effect on Photosynthesis
In support of the involvement of H 2 O 2 in the photosynthetic reaction, several
H 2 O 2 -related phenomena have been observed in natural waters, which can be classified as follows (Mostofa et al. 2009). First, the correlation between carbon production and photolytically formed H 2 O 2 concentration, suggesting a link between
hydrogen peroxide and organic matter photosynthesis in lake water (Anesio et al.
2005). Second, Chl a production in the epilimnetic layer (5–10 m) is typically
observed to increase with a decrease in total CO 2 contents (Talling 2006), suggesting that photosynthesis is highest at the epilimnetic layer (5–10 m) than in
the uppermost epilimnion (0–1 m). Correspondingly, the O 2 and Chl a contents
reach a minimum when the water temperature become highest during the summer
stratification period (Talling 2006), suggesting that photoinduced degradation or
assimilation of Chl a may be responsible for the decrease in Chl a at the uppermost layer. Here O 2 may be involved in the production of free radicals (H 2 O 2 or
HO
•
) that could inhibit photosynthesis (Mostofa and Sakugawa 2009; Moffett and
Zafiriou 1990). This result is similar to earlier studies where photosynthesis was
observed to be less effective in the uppermost layer (1 m) compared to the subsequent epilimnion (3 m) (Nozaki et al. 2002). A ratio of variable to maximal fluorescence (Fv/Fm) of phytoplankton productivity showed a decrease as irradiance
increased during the morning and an increase as irradiance declined in the afternoon. These results may be associated with both photoprotective strategies in the
antennae of PSII and photo damage of PSII reaction centers (Zhang et al. 2008).
Conversely, H 2 O 2 usually increases gradually starting in the morning, reaches a
maximum at noon and then gradually decreases in the afternoon (Mostofa and
Sakugawa 2009). It is therefore suggested that high production of H 2 O 2 and subsequent photoinduced generation of HO
• at noon is susceptible to damage the PSII
reaction centers.
Third, H 2 O 2 may be concentrated by particulate organic matter or small fungi
through rapid transpiration (Komissarov 1994, 1995, 2003). This hypothesis
can be supported by observation of relatively low production of H 2 O 2 in unfiltered samples compared to filtered ones during irradiation (Moffett and Zafiriou
1990; Cooper et al. 1988; Petasne and Zika 1997). An increase in the growth rate
of plants and mycelial fungi is detected when the H 2 O 2 concentration increases
up to an optimum level, from 1 nM to 10 M, and the growth rate decreases when
H 2 O 2 approaches 1 mM (Komissarov 2003; Ivanova et al. 2005). High levels of
H 2 O 2 may photolytically produce HO
•
, a strong oxidizing agent, that may cause
ecophysiological disorders in plants, decrease the CO 2 assimilation rate and
affect stomatal conductance, fluorescence and needle life span (Kume et al. 2000;
Kobayashi et al. 2002). In natural waters, HO
• that is produced photolytically from