736
K. M. G. Mostofa et al.
Photoinduced Generation of Hydroxyl Radical in Natural Waters”, and “Complexation
of Dissolved Organic Matter with Trace Metal ions in Natural Waters”). The transformation of FCCs to NCCs can be depicted shortly as below (Eqs. 5.1–5.4):
where FCCs upon illumination by light are excited and produce e − , (Eq. 5.1) which
then reacts with aqueous dissolved oxygen to generate O 2
•− (Eq. 5.2). O 2
•− then
produces H 2 O 2 and subsequently HO
• upon several pathways as mentioned earlier
(Eq. 5.3). The HO • radical can then react with FCC + to convert it into FCCs-OH
and then into NCCs-OH (Eq. 5.4). Organic peroxides (ROOH) are produced either
by similar processes or by breakdown of other organic components. They can generate the organic peroxide radical (RO
•
) and give NCC-OR. These reactions are
extensively discussed in earlier chapters (see chapters “Photoinduced and Microbial
Generation of Hydrogen Peroxide and Organic Peroxides in Natural Waters and
Photoinduced and Microbial Degradation of Dissolved Organic Matter in Natural
Waters”). Such a mechanism can also be supported by the observation that Chl degradation of chloroplast lysate or leaf extracts can be induced by intrinsic (per)oxidation
with phenolic compounds and H 2 O 2 , and by lipoxygenation with linolenic acid (‘oxidative Chl bleaching’) (Janave 1997; Johnson-Flanagan and Spencer 1996; Adachi et
al. 1999). Similarly, peroxidase or oxidase activity rise in parallel to the degreening
of seeds or cotyledons in some plants (Johnson-Flanagan and Spencer 1996; Adachi
et al. 1999). Therefore, HO
• or RO
• may play a significant role in the transformation
of FCCs to NCCs in vacuole. Chl breakdown is a prerequisite to detoxify potentially
phototoxic pigments within the vacuoles, to allow the remobilization of nitrogen from
Chl-binding proteins that takes place during senescence (Hörtensteiner 2006).
On othe other hand, Chl b is degraded to chlorophyllide b by chlorophyllase, then chlorophyllide b is converted to chlorophyllide a by ‘Chl b reductase’
(Schelbert et al. 2009; Ito et al. 1996; Folly and Engel 1999; Scheumann et al.
1999; Tanaka and Tanaka 2006; Rüdiger 2003). The further degradation of chlorophyllide a proceeds in similar ways as mentioned before.
6 Chl Acting as Universal Signature of Cyanobacteria
(Algae) or Phytoplankton Dynamics
Chl a concentrations are very variable in waters, ranging from 0.0 to 280 μg L −1 in
streams and rivers, 0.01–850 μg L −1 in lakes, 0.0–919 μg L −1 in reservoirs, 0.0–
220 μg L −1 in estuaries, 0.0–2080 μg L −1 in coastal and marine waters, and 0.06–
1,000 μg L −1 in ice-covered Arctic and Antarctic Oceans (Table 1). Changes in Chl a
(5.1)
FCCs + hυ → FCCs
+ + e
−
(5.2)
e
− + O 2 → O
•−
2
(5.3)
O
•−
2 + 2H
+ → H 2 O 2 → HO
•
(5.4)
FCC
+ + HO
• → FCC − OH → NCC − OH
K. M. G. Mostofa et al.
Photoinduced Generation of Hydroxyl Radical in Natural Waters”, and “Complexation
of Dissolved Organic Matter with Trace Metal ions in Natural Waters”). The transformation of FCCs to NCCs can be depicted shortly as below (Eqs. 5.1–5.4):
where FCCs upon illumination by light are excited and produce e − , (Eq. 5.1) which
then reacts with aqueous dissolved oxygen to generate O 2
•− (Eq. 5.2). O 2
•− then
produces H 2 O 2 and subsequently HO
• upon several pathways as mentioned earlier
(Eq. 5.3). The HO • radical can then react with FCC + to convert it into FCCs-OH
and then into NCCs-OH (Eq. 5.4). Organic peroxides (ROOH) are produced either
by similar processes or by breakdown of other organic components. They can generate the organic peroxide radical (RO
•
) and give NCC-OR. These reactions are
extensively discussed in earlier chapters (see chapters “Photoinduced and Microbial
Generation of Hydrogen Peroxide and Organic Peroxides in Natural Waters and
Photoinduced and Microbial Degradation of Dissolved Organic Matter in Natural
Waters”). Such a mechanism can also be supported by the observation that Chl degradation of chloroplast lysate or leaf extracts can be induced by intrinsic (per)oxidation
with phenolic compounds and H 2 O 2 , and by lipoxygenation with linolenic acid (‘oxidative Chl bleaching’) (Janave 1997; Johnson-Flanagan and Spencer 1996; Adachi et
al. 1999). Similarly, peroxidase or oxidase activity rise in parallel to the degreening
of seeds or cotyledons in some plants (Johnson-Flanagan and Spencer 1996; Adachi
et al. 1999). Therefore, HO
• or RO
• may play a significant role in the transformation
of FCCs to NCCs in vacuole. Chl breakdown is a prerequisite to detoxify potentially
phototoxic pigments within the vacuoles, to allow the remobilization of nitrogen from
Chl-binding proteins that takes place during senescence (Hörtensteiner 2006).
On othe other hand, Chl b is degraded to chlorophyllide b by chlorophyllase, then chlorophyllide b is converted to chlorophyllide a by ‘Chl b reductase’
(Schelbert et al. 2009; Ito et al. 1996; Folly and Engel 1999; Scheumann et al.
1999; Tanaka and Tanaka 2006; Rüdiger 2003). The further degradation of chlorophyllide a proceeds in similar ways as mentioned before.
6 Chl Acting as Universal Signature of Cyanobacteria
(Algae) or Phytoplankton Dynamics
Chl a concentrations are very variable in waters, ranging from 0.0 to 280 μg L −1 in
streams and rivers, 0.01–850 μg L −1 in lakes, 0.0–919 μg L −1 in reservoirs, 0.0–
220 μg L −1 in estuaries, 0.0–2080 μg L −1 in coastal and marine waters, and 0.06–
1,000 μg L −1 in ice-covered Arctic and Antarctic Oceans (Table 1). Changes in Chl a
(5.1)
FCCs + hυ → FCCs
+ + e
−
(5.2)
e
− + O 2 → O
•−
2
(5.3)
O
•−
2 + 2H
+ → H 2 O 2 → HO
•
(5.4)
FCC
+ + HO
• → FCC − OH → NCC − OH