Biology Reference
In-Depth Information
regions. The modulation of antioxidant enzyme activities with respect to changing
radiation and temperature regimes in the course of the seasons has been observed
for a number of macroalgal species from an Arctic fjord system: Kongsfjorden,
Svalbard (Aguilera et al.
2002a
). It was striking that macroalgae growing
subtidally, such as the chlorophyte
Monostroma
sp. and the rhodophyte
Palmaria
palmata
, showed patterns of antioxidant enzyme activity modulation, which were
corresponding to seasonal changes but also to their respective growth site and,
furthermore, life strategy. In
Monostroma
sp
.
and
P. palmata
, SOD activities
closely reflected the particular PAR and UV radiation conditions in Kongsfjorden:
SOD activities were low as long as the coastline was still covered by sea ice until
the middle of June. Thus, these subtidal organisms were exposed to prolonged
conditions of extreme low light. The sea ice breakup may then occur rapidly within
very few days and is mainly triggered by changes in the hydrographic conditions of
the fjord (Svendsen et al.
2002
). Accordingly, seaweeds which were exposed to
darkness or very low light conditions during the polar night and under the prolonged
sea ice cover may then rapidly be exposed to high irradiances of PAR and UV
radiation because of the subsequent very clear water conditions. Therefore, high
radiation is able to penetrate deeply into the water column and thus even affects
subtidal macroalgae significantly.
Monostroma
sp
.
responded to the breakup of sea
ice with more than a doubling of total SOD activity within very few days and with a
continued increase as long as the seawater remained clear. Simultaneously, the
detected loss of GR activity might either be a result of increased CAT activities or a
consequence of direct radiation damage (Aguilera et al.
2002a
).
Palmaria palmata
even quadruplicates SOD activity in summer, but this response was much slower
than in
Monostroma sp
. Moreover, this increase was still ongoing throughout the
summer season and may thus reflect an acclimation pattern to the season. In
contrast, SOD activity in
Monostroma sp.
peaked just before the onset of snow-
melt inshore and consequently the runoff of turbid freshwater. These events
resulted in an increase of suspended material in the water column, leading to a
strong decrease in water transparency and thus decline in in situ light exposure.
Consequently, SOD activities might well be reduced again under subsequent turbid
water conditions. Overall, this very flexible seasonal response in SOD activity of
Monostroma sp.
is in line with the purely opportunistic life strategy of this
ephemeric green alga. In contrast to both species described above, the shallow
water red alga
Devaleraea ramentacea
did not exhibit marked variation of SOD
activity in the course of the seasons. It rather maintained high SOD activities
throughout the year, even under low light conditions under sea ice cover. This is
typically characterizing
D. ramentacea
as a shallow water species and is in line with
the generally reduced habitat stability, being exposed to more pronounced variation
in physicochemical variables in shallow waters.
In summary, high interspecific variation in SOD activity has been demonstrated
in a multitude of studies, reflecting species-specific differences with respect to the
respective growth site along latitudinal and depth gradients, with respect to site-
specific seasonal variation, as well as differences with respect to developmental
stages, age, and tissue type under investigation. Oxidative stress is also to be
