Biology Reference
In-Depth Information
(Bischof et al.
1998
; see Chap.
20
by Bischof and Steinhoff), this factor did not
seem to play a major role in ROS formation under the experimental conditions
tested, since SOD activities did not increase, even not in individuals from the
deepest collection site. Also, results obtained do not point to a highly flexible
response of SOD adjustment, at least not within the 4 h of experimental exposure.
Thus, data obtained rather reflect long-term acclimatory adjustments, potentially
allowing the efficient detoxification of light-induced superoxide in individuals from
the upper and mid sublittoral (5.5 and 9.0 m), where irradiance conditions may
increase and may become harmful to photosynthesis on sunny days, as soon as noon
coincides with low tides. In contrast, low SOD activities shown for the deep-water
individuals (13.5 m water depth) reflect the larger degree of habitat stability as e.g.,
the extent of attenuation of solar radiation by the water column above and the in situ
radiation climate. However, high SOD activities of
D. anceps
are presumably
achieved by increasing the cellular content of the scavenging enzyme rather than
by modification to the protein itself. Consequently, higher energetic costs for
protein biosynthesis might then be compensated by higher photosynthetic activities
as demonstrated in
D. anceps
from the upper sublittoral.
As outlined above, the variation in SOD activity described in individuals of
D. anceps
resulted from site-specific differences in habitat stability and light
attenuation along the depth gradient, in the present case approximately 10 m.
Other studies, however, explored whether changes in SOD activities are also
significant along microscale gradients of light exposure, e.g., within algal canopies
where irradiance might be diminished within just a few centimeters. In fact, in
dense algal assemblages exposed to high solar irradiance, distinct responses of SOD
activities toward variation in light quantity and quality have been observed in green
algal mats of
U. rotundata
and
C. linum
(Bischof et al.
2002
,
2003
,
2006
). Results
obtained over microscale gradients confirmed the findings on
D. anceps
that overall
SOD activity represents well the in situ radiation climate and thus the vertical
position of respective specimens, but does not exhibit changes in activity and thus
flexible adjustments under experimental conditions. These adjustments seem to
require a longer exposure to the respective environmental conditions in order to
become significant. Thus, the studies mentioned above did not exhibit changes in
SOD activity along diurnal or tidal cycles.
6.3.2 Seasonal Changes in SOD Activity in Seaweeds
from an Arctic Fjord
The ecological implications of adjustments of the antioxidant metabolism become
apparent when considering pronounced
seasonal
changes in abiotic conditions at
the natural growth sites of seaweeds. In particular, polar regions represent a good
example for such studies because the abiotic environment of macroalgae changes
more drastically throughout the seasons than it does in temperate or tropical
