Biology Reference
In-Depth Information
The supralittoral species
Prasiola crispa
has even a broader growth range between
0.3 and 105 psu (Karsten et al.
1991a
,
b
; Jacob et al.
1991
). The general mechanisms
of osmotic acclimation are the same as also in species from other regions (Kirst
1990
; Wiencke et al.
2007
; see Chap.
5
by Karsten). Major inorganic osmolytes are
potassium, sodium, and chloride. These osmolytes are used during short-term
osmotic regulation. Long-term osmotic stress is counterbalanced by various com-
patible organic solutes, among them
b
-dimethylsulphoniumproprionate (DMSP),
the imino acid proline, and sucrose (Karsten et al.
1991b
; Jacob et al.
1991
).
Decreasing temperatures also strongly stimulate the biosynthesis and accumula-
tion of DMSP in Antarctic green algae stabilizing the structure of the enzymes
lactate dehydrogenase and malate dehydrogenase of
Acrosiphonia arcta
(Karsten
et al.
1996
). Ice-binding proteins (IBP) that modify the shape of growing intracel-
lular ice crystals during freezing were recently detected in Antarctic
Prasiola
and
sea-ice diatoms (Raymond and Fritsen
2001
). Presumably, IBPs prevent damage to
membranes by the inhibition of the recrystallization of ice (Raymond and Knight
2003
).
The low temperatures in the eulittoral and supralittoral represent a challenge to
algal physiology because they are often combined with high irradiances in summer.
At low temperatures enzyme activities and turnover velocity of the D1 reaction
center protein in photosystem II are reduced (Andersson et al.
1992
; Aro et al.
1993
), which may result in increased electron pressure in photosynthesis and
ultimately in the generation of reactive oxygen species (Dring
2006
). The
consequences of increased oxidative stress are chronic photoinhibition/photoinac-
tivation, bleaching of photosynthetic pigments, peroxidation of membrane lipids,
and enhanced degradation of D1 protein (see Chap.
6
by Bischof and
Rautenberger). Eulittoral species, such as the green algae
Urospora penicilliformis
and
Ulva hookeriana
, the red alga
Porphyra endiviifolia
, and the brown alga
Adenocystis utricularis
may overcome radiation stress at low temperatures by
their ability for dynamic photoinhibition/photoprotection, which proceeds much
faster than in sublittoral algae (Hanelt et al.
1994
,
1997
). In the upper sublittoral red
alga
Palmaria decipiens
, for example, there was a persistent impairment of photo-
synthetic activity at 0
C combined with irradiances of 400
m
mol photons m
2
s
1
,
but not at 200
mol photons m
2
s
1
. In contrast, photosynthesis was not impaired
under both light intensities at 8
C (Becker et al.
2011
).
The effects of freezing in combination with high light intensities on photosyn-
thesis were studied in the Arctic eulitttoral brown alga
Fucus distichus
. There was a
marked decrease of optimum quantum yield with decreasing temperatures down to
m
15
C and a rapid recovery as soon as the temperatures increased again
(Becker et al.
2011
). While photosynthetic activity was zero at 15
C in this species,
in the Antarctic green alga
Prasiola
photosynthetic activity was observed down to
10/
15
C (Becker
1982
). The physiological basis of this extraordinary capacity is not
known.
Desiccation is a strong stress parameter in supralittoral species (see also Chap.
5
by Karsten). Thalli of
Prasiola crispa
lose 75% of the cellular water during the first
6 h of exposure to air (Jacob et al.
1992
). Irreversible damage occurred after a water
