Environmental Engineering Reference
In-Depth Information
A recent study has shown that the PSII monomer consists of 1300 H
2
O mole-
cules, a few of which have been detected as disordered (Umena et al.
2011
). H
2
O
2
was not considered as a component of PSII structure in that study. Concurrently,
four successive photoinduced turnovers provide the WOC with four oxidising
equivalents and drive it through an S-state cycle, with S-states ranging from S
0
to
S
4
and O
2
is being released on the S
3
to S
4
transition.
Now the questions are: how is it possible for H
2
O to undergo photodissocia-
tion through four successive photoinduced turnovers, needing energy in the pres-
ence of H
2
O
2
that can easily be decomposed and produce O
2
? How can H
2
O in a
cell accept four consecutive electrons in the presence of many additional compo-
nents including O
2
that can more easily accept electrons? Under these conditions,
the easiest pathway would be the addition of one electron to O
2
with formation
of
O
2
•−
and then of H
2
O
2
. This is a well established mechanism in water media
and could take place in photosynthetic cells as well. Note that the main radia-
tion absorbers in natural waters are chromophoric (or colored) DOM (CDOM)
(10-98 %), phytoplankton or chlorophyll (32-85 %), H
2
O (0.3-9 % in the red
portion of the visible spectrum, depending on water being clear or turbid) and so
on (see chapter
“
Colored and Chromophoric Dissolved Organic Matter in Natural
electrons under light condition in the presence of O
2
or other organic components
in a photosynthetic cell and there is no evidence in that regards.
It is therefore theorized that
if H
2
O would decompose by the reaction with CO
2
in photosynthesis, then all H
2
O would
convert into O
2
by organisms and plants after the origin of life on earth to date and no
H
2
O would remain in the biosphere. Instead of H
2
O, photoinduced generation of H
2
O
2
from dissolved O
2
in water bound in photosynthetic cells (
3.33
-
3.39
) is reacted with CO
2
in photosynthesis that can limit the photosynthesis under light condition.
Then further conversion of H
2
O
2
to O
2
either through photosynthesis [
X
CO
2
(
H
2
O
)
+
Y
CO
2
(
H
2
O
)
→
C
x
(H
2
O)
y
+
O
2
+
E (
±
)] or both photolytically (2H
2
O
2
+
h
υ
→
O
2
+
unknown oxidant) and biologically (2H
2
O
2
+
catalases/peroxidases
→
O
2
+
2H
2
O) may balance the environment.
This can be supported by the observation of several phenomena:
(i) Formation and occurences of H
2
O
2
in photosynthetic cells of organ-
isms through production of O
2
•
−
from whole bacteria of several species, from
phagocytic cells, from spermatozoa as well as peroxisoms, mitochondria and
chloroplasts (Komissarov
2003
; Bach
1894
; Chance et al.
1979
; Halliwell
1981
;
Holland et al.
1982
; Wilhelm et al.
1996
,
1997
,
1999
; Halliwell and Gutteridge
1999
; López-Huertas et al.
1999
; Baker and Graham
2002
; del Río et al.
2006
;
Krieger-Liszkay et al.
2008
; Lyubimov and Zastrizhnaya
1992a
,
b
; Turrens
1997
; Karuppanapandian et al.
2011
). (ii) Releases of O
2
from H
2
O
2
dur-
ing photosynthesis are evidenced in earlier studies (Komissarov
1994
,
2003
;
Velthuys and Kok
1978
; Asada and Badger
1984
; Asada and Takahashi
1987
;
Mano et al.
1987
; Renger
1987
; Anan'ev and Klimov
1988
; Bader and Schmid
1988
,
1989
; Schroeder
1989
; Schröder and Åkerlund
1990
; Miyake and Asada
1992
; Kuznetsov et al.
2010
; Bernardini et al.
2011
; Yin et al.
2006
). (iii) The
