Environmental Engineering Reference
In-Depth Information
Functions of Chls and their degradation products can be discriminated as fol-
lows: (i) Chl is an efficient visible-light photosensitizer and a key component
required for the absorption of sunlight. It is essential for the occurrence of photo-
synthesis as it is involved into the initiation of electron release in aquatic micro-
organisms and higher plants (see also chapter
“
Photosynthesis in Nature: A New
Look
”) (Hörtensteiner and Kräutler
2011
; Foote
1976
; Kimball
1979
; Knox and
Dodge
1985
). Under specific conditions (e.g. high light conditions, high temper-
ature, drought and so on) Chl can significantly produce reactive oxygen species
(ROS) such as singlet oxygen (
1
O
2
), superoxide radical anion (O
2
•
−
), hydrogen
peroxide (H
2
O
2
) and HO
•
(see chapter
“
Photosynthesis in Nature: A New Look
”).
In turn, these species can degrade Chl and cause cell death (Rontani
2001
;
Hörtensteiner and Kräutler
2011
; Marshall et al.
2002
; Oda et al.
1998
). ROS also
play a role during senescence of photosynthetic cells or fruit ripening. Strong light
gradients cause unbalanced excitation of the two photosystems and reduce pho-
tosynthetic efficiency (Dietzel et al.
2011
). (ii) According to the Treibs hypoth-
esis, petroporphyrins can originate from Chl (Treibs
1936
; Liang et al.
1993
).
(iii) Chl, some of its synthetic analogues, metal complexes of porphyrins and phth-
alocyanines are all photoactive. As key components bound to organisms they can
cause production of H
2
O
2
in vivo under light, in aqueous solutions saturated with
dioxygen (Hong et al.
1987
; Bazanov et al.
1999
; Premkumar and Ramaraj
1999
;
Lobanov et al.
2008
). (iv) Chls, the pigments responsible for green color in fruits
and vegetables, are highly susceptible to degradation during processing. This can
result into changes from bright green to olive brown or other colors, during stor-
age and processing in the agriculture and food industry (Schwartz and von Elbe
1983
; Sweeney and Martin
1961
). Color, the major quality attribute of vegetables
and fruits, is a key factor in the commercial value of food to the consumer and
can be highly affected by Chl breakdown as an important catabolic process of leaf
senescence and fruit ripening (Takamiya et al.
2000
; Hörtensteiner and Kräutler
2011
; Schwartz and von Elbe
1983
; Steet and Tong
1996
). (v) The colorless “non-
fluorescent Chl catabolites (NCC)” found in ripening fruits (e.g. apples and pears)
can act as antioxidants, in a similar way as bilirubin (Moser et al.
2009
; Stocker
et al.
1987
; Barañano et al.
2002
). It has been shown that the rates of formation of
hydroperoxides of linoleic acid in the presence of NCC is significantly reduced.
The observed effect is a function of time and of the concentration of the added
antioxidants. Moreover, the (concentration-dependent) peroxy radical scaveng-
ing effect of NCC is only slightly inferior to that of bilirubin (Moser et al.
2009
;
Stocker et al.
1987
; Müller et al.
2007
). (vi) Chl
a
is generally used to estimate
the primary biomass production or the phytoplankton/cyanobacterial biomass or
bloom in natural waters. In contrast, carotenoids and the degradation intermediates
xanthophylls could be effective biomarkers of different classes of phytoplankton
(Fielding and Seiderer
1991
; Ondrusek et al.
1991
; Williams and Claustre
1991
;
Millie et al.
1993
; Jeffrey et al.
1999
; Bianchi et al.
1993
,
2002
; Kasprzak et al.
2008
). Therefore, Chl
a
and its degradation products could be useful indicators
of the fate and composition of phytoplankton species and of transformation and
degradation of phytoplanktonic carbon. As a key characteristic of phototrophic
