Environmental Engineering Reference
In-Depth Information
In addition, resistance to salinity may occur when a plant is capable of producing
large amounts of antioxidant enzymes such as superoxide dismutase (SOD), ascorbate
peroxidase (APX) and glutathione reductase (GR) (Asada
1992
; Prochazkova and
Wilhelmova
2007
; Mittova et al.
2002
; Gossett et al.
1994
; Pastori and Trippi
1993
).
These enzymes can significantly scavenge free radicals under stress conditions.
Elevated levels of GR are capable of increasing the amount of NADP
+
, which
accepts electrons from the photosynthetic electron transport chain (Peltzer et al.
2002
; Reddy et al.
2004
). The activity of antioxidant enzymes under saline con-
ditions are typically increased in the case of salt-tolerant cotton varieties, shoot
cultures of rice, cucumber, wheat shoot and pea (Bybordi et al.
2010b
,
c
; Meloni
et al.
2003
; Desingh and Kanagaraj
2007
; Fadzilla et al.
1997
; Lechno et al.
1997
;
Hernandez et al.
1999
; Meneguzzo et al.
1999
). Due to salinity stress, plants can
accumulate osmolytes such as proline and glycine betaine, which are known to
protect macromolecules by stabilizing protein structure during dehydration and/
or by scavenging ROS produced under stress conditions (Desingh and Kanagaraj
2007
; McNeil et al.
2001
; Zhu
2001
; Matysik et al.
2002
; Rontein et al.
2002
).
Tolerance of photosystems to salt stress can be enhanced by genetically engi-
neered increase in the unsaturation of fatty acids in membrane lipids, and by intra-
cellular synthesis of compatible solutes (e.g. glucosylglycerol and glycinebetaine)
(Allakhverdiev and Murata
2008
). When photosynthetic organisms are exposed
to salt stress, fatty acids of membrane lipids are desaturated (Huflejt et al.
1990
).
Therefore, unsaturation of fatty acid in membrane lipids can enhance tolerance of
PSI and PSII to salt stress (Allakhverdiev and Murata
2008
).
Enhanced tolerance of PSII to salt stress upon unsaturation of membrane lipids is
probably accounted for by the fact that unsaturated fatty acids are generally capable of
surrounding the cations [e.g. Na
+
/H
+
antiporter(s) and/or H
+
-ATPase(s)] with their
electron-rich double bonds. An increase in the levels of the antiport system components
can decrease the concentration of Na
+
ions in the cytosol, which may protect PSII and
PSI against NaCl-induced inactivation (Allakhverdiev and Murata
2008
).
5.9 Effects of Toxic Pollutants on Aquatic Microorganisms
Environmentally-occurring toxic organic pollutants can decrease the efficiency
of photosynthesis, most presumably by adversely affecting the PSII (Berden-
Zrimec et al.
2007
; Mayer et al.
1997
; Halling-Sørensen et al.
2000
; Katsumata
et al.
2005
,
2006
; Kvíderová and Henley
2005
; Zrimec et al.
2005
;
Pan et al. 2009
;
Yates and Rogers
2011
). Some antibiotics (e.g. ampicillin, streptomycin, levo-
floxacin hydrochloride, mecillinam, trimethoprim, ciprofloxacin), phenols (e.g.
3,5-dichlorophenol), pesticides and herbicides (e.g. DCMU or diuron, simazine,
atrazine) are highly toxic to microorganisms such as cyanobacteria or phytoplank-
ton cells (Berden-Zrimec et al.
2007
; Halling-Sørensen et al.
2000
; Katsumata
et al.
2005
,
2006
Kvíderová and Henley
2005
; Zrimec et al.
2005
; Pan et al.
2009
;
Yates and Rogers
2011
; DeLorenzo et al.
2001
). The toxic organic compounds
