Biology Reference
In-Depth Information
ROS-scavenging mechanisms in order to protect against cytotoxic reactive oxygen.
These mechanisms include the inducible increase in activities of the radical scaveng-
ing enzymes SOD, APX, GR as well as the cellular concentration of antioxidants, e.g.,
glutathione, ascorbate, carotenoids (Aguilera et al.
2002b
;Dummermuthetal.
2003
).
SOD has often been referred to as “the first line of defence” against ROS.
However, in most of the studies conducted on SOD activity in macroalgae so far,
it was not discriminated between the different isoforms of SOD, the cytosolic Cu/
Zn-SOD or the Fe-SOD located in chloroplasts, neglecting the assumption that it is
indeed the combination and interaction of different isoforms of SOD characterizing
it as the central protection mechanisms against O
2
-mediated damage (Pinto et al.
2003
; see Dring
2005
). Variation in total SOD activity has been found among
different seaweed species and also with respect to the respective growth site, i.e.,
abiotic stress exposure along latitudinal or vertical gradients (Aguilera et al.
2002b
). In general,
inter
specific differences in SOD activity are mostly related to
differences in the respective abiotic environment of the species under investigation,
depending on latitudinal differences, but also the shore level, which is typically
populated by the respective species. In their survey on general antioxidative
properties of polar macroalgae, Aguilera et al. (
2002b
) reported on an interspecific
depth-dependent antioxidative pattern: species from the upper shore are generally
characterized by higher SOD activities than those from deeper growth sites as a
likely consequence of high light exposure.
Latitudinal differences in SOD activity were found in the closely related green
macroalgae
Ulva bulbosa
(now also referred to as
U. hookeriana
) and
Ulva
clathrata
from Antarctic and sub-Antarctic regions, respectively (Rautenberger
and Bischof
2006
). Total SOD activities in
U. bulbosa
were significantly higher
(86-89 Units mg
1
protein) compared to those in
U. clathrata
(58-63 Units mg
1
protein). Apparently, these differences based on the respective geographical dis-
persal of these species are resultant from differences in water temperature and
radiation regimes, modulated by latitude. The Antarctic ecotype of
U. bulbosa
is
permanently exposed to lower water temperatures (around 0
C) than
U. clathrata
isolated from waters in which temperatures never decrease below 5
C. Exposure to
lower water temperatures may permanently cause a higher background level of
ROS in
U. bulbosa
which requires a more efficient detoxification system, reflected
by the higher SOD activity. Furthermore,
U. bulbosa
's lower susceptibility to
enhanced irradiances of UV-B radiation at 0
C might be a consequence of a
more efficient photoprotection, possibly achieved by higher SOD activities as well.
On a smaller spatial scale, i.e., with respect to growth at different shore levels,
the related intertidal rhodophytes
Mastocarpus stellatus
and
Chondrus crispus
(Gigartinales) have been tested for their respective total scavenging activity of
SOD, which was found to be clearly related to general stress tolerance (freezing,
high light, temperature) and tidal height (Coll´n and Davison
1999c
; Bischof et al.
2000
; Lohrmann et al.
2004
). Also, different intertidal congener species of the
brown alga
Fucus
display differential overall activities of SOD, positively
correlated with the respective position of the respective species on the shore (Coll
´
n
and Davison
1999a
,
b
).
