Biology Reference
In-Depth Information
mechanism under conditions of restricted electron drainage, resultant from e.g.,
saturated photosynthetic secondary reactions (i.e., Calvin-Benson cycle) and accu-
mulation of reduced NADP (NADPH
H
+
). These conditions are typically
induced under excessive irradiance conditions. Nowadays, it is common knowledge
in plant sciences that a sudden exposure to high irradiance of photosynthetically
active radiation (PAR: 400-700 nm) may impair or even destruct the photosynthetic
apparatus, particularly in low light adapted plants (Andersson et al.
1992
; Osmond
1994
). Excessive radiation conditions may thus result in an inhibition of photosyn-
thesis, called photoinhibition (Aro et al.
1993
; Osmond
1994
; Hanelt
1996
; Franklin
et al.
2003
; see Chap.
1
by Hanelt and Figueroa). Furthermore, studies on intertidal
seaweeds have shown that besides excessive radiation most other environmental
factors leading to physiological stress, like e.g., freezing, desiccation, hypo- and
hypersalinity, heavy metals, as well as wounding may accelerate the cellular pro-
duction of ROS (Benet et al.
1994
; Coll´n and Davison
1999a
,
b
; Burritt et al.
2002
;
Lu et al.
2006
; Pereira et al.
2009
; Wu et al.
2009a
,
b
; see also Chap.
5
by Karsten). In
general, if accumulation of ROS exceeds the scavenging capacity of enzymatic and
nonenzymatic antioxidant systems, remaining non-detoxified ROS may inhibit
photosynthesis and become auto-destructive to cells due to the oxidation of lipids,
proteins, and nucleic acids. Consequently, the ability to control oxidative stress, i.e.,
to limit the generation of ROS effectively, is an important feature of organisms
inhabiting variable environments. It is, thus, of vital importance to e.g., intertidal
macroalgae to suppress or remove stress-induced ROS in order to thrive in their
challenging habitat [see Davison and Pearson (
1996
) for review]. Particularly in the
intertidal, macroalgae are subjected to a highly variable environment, which
requires permanent adjustments of metabolic rates and protective strategies to
keep oxidative stress at minimum, nondestructive levels. Most intertidal macroalgae
are exposed to large fluctuation in irradiance levels, i.e., when low tide coincides
with high solar radiation conditions around noon (Davison and Pearson
1996
).
Furthermore, drastic changes in (air and water) temperatures, salinity, desiccation,
as well as mechanical forcings represent significant stress factors to intertidal
macroalgae with implications to the respective reactive oxygen metabolism (Coll´n
and Davison
1999a
; Burritt et al.
2002
; Sung et al.
2009
).
Besides its major role in stress responses and as mediator of cellular damage,
ROS also have been identified forming an important component in signal transduc-
tion pathways (Mackerness et al.
2001
) and even interspecific interactions. The
function in pathogen defence or fouling control via oxidative bursts has been
proven by the light-independent release of H
2
O
2
triggered by membrane-bound
NADPH oxidases (Potin
2008
). The present contribution, however, focuses on the
stress-mediated induction of ROS, forced by the respective abiotic environment and
highlights adaptive and acclimatory traits in macroalgae to cope with oxidative
stress in particular with respect to superoxide dismutase (SOD) activity. For
extended information on the significance of reactive oxygen to seaweed physiology
and biotic interactions, the reader is referred to the recent and very comprehensive
reviews by Dring (
2005
) and Potin (
2008
).
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