Biology Reference
In-Depth Information
6.3.1 SOD Activity in the Brown Seaweed
Desmarestia anceps
Along a Depth Gradient: A Case Study in Antarctica
In line with
inter
specific variation of SOD activity along gradients of different
spatial scales, also
intra
specific variations have been found, reflecting the specific
abiotic conditions in individuals of species growing over pronounced latitudinal
and/or vertical ranges.
The variation of SOD activity with depth was studied in an ecologically important
brown seaweed fromAntarctica (Rautenberger and Bischof, previously unpublished
data): The endemic Antarctic phaeophyte
Desmarestia anceps
colonizes water
depths between 5 and 30 m in coastal ecosystems (see also Chap.
13
by Wiencke
and Amsler). Occurring across such a wide range within the sublittoral zone, this
species is subjected to a pronounced vertical gradient of habitat stability. Thus,
individuals from highest positions on the shore are regularly exposed to frequent and
strong changes in abiotic conditions, such as solar radiation, whereas specimens
from deeper waters inhabit a much more stable environment. It was, thus, expected
that
D. anceps
has a high potential to respond to environmental changes at the
individual growth sites by metabolic adjustments to the respective in situ conditions.
Overall, the species-specific capacity to detoxify ROS with respect to environ-
mental stability, also including the exposure to detrimental UV-B-radiation, is a
major factor determining the vertical distribution patterns of seaweeds on the shore
(Bischof et al.
1998
; Aguilera et al.
2002b
; see Chap.
20
by Bischof and Steinhoff).
In
D. anceps
, site-specific variation of total SOD activity as a function of water
depth was investigated in adult sporophytes. Individuals were collected at 5.5, 9.0,
and 13.5 m water depth, near the Antarctic scientific base Jubany (62.23
S,
58.63
W) at King George Island (South Shetland Islands, Antarctic Peninsula) in
January 2005. Specimens were cultivated in air-bubbled basins in the laboratory at
15
mol m
2
s
1
PAR (16:8 h light/dark) and 2
1
C for 10 days. Changes in
SOD activity in response to exposure to enhanced ultraviolet radiation were studied
by supplementing the PAR regime with 15.3 W m
2
UV-A and 2.2 W m
2
UV-B.
For exposure, Petri dishes containing the specimens were completely covered by
cutoff filters in order to expose experimental individuals to a defined spectral
composition: PAR alone (400-700 nm), PAR + UV-A (320-700 nm), and PAR +
UV-A + UV-B (280-700 nm). Consequently, the integral UV-B dose over the
entire experimental period of 4 h was 31.8 kJ m
2
and the three radiation treatments
were used to study
D. anceps
' potential to acclimate to enhanced UV-B radiation by
SOD adjustment. SOD activities were determined according to a modified xanthine/
xanthine oxidase assay of McCord and Fridovich (
1969
) and Aguilera et al. (
2002b
)
at 25
C. Initial total SOD activities (PAR alone) were related to the original water
depths where the individuals of
D. anceps
have grown before collection (Fig.
6.1a
).
Individuals obtained from 5.5 m exhibited very high activities of 2,760
m
2,283
Units mg protein
1
. Although SOD activities of 1,389
559 Units mg protein
1
determined in individuals from 9.0 m showed a trend to lower values, there was no
statistical difference in SOD activity in specimens from both depths. However,
