Biology Reference
In-Depth Information
Wiencke
2000
) and was also found for cold-temperate specimens of the kelp
Saccharina latissima
(Davison et al.
1991
) and the red macroalga
Chondrus crispus
(K
ubler and Davison
1995
).
Photosynthetic adjustments in response to a change in growth temperature take
place in order to counteract the imbalance between photosynthetic energy production
and cellular energy consumption (Wilson et al.
2003a
). Low-temperature acclimated
Chlorella vulgaris
cells exhibit high chlorophyll
a
:
b
ratio, low light-harvesting
complex polypeptide abundance, and an increased zeaxanthin content (Wilson and
Huner
2000
). Machalek et al. (
1996
) describe in
Saccharina latissima
a decrease in
concentration of major light-harvesting pigments when grown at suboptimal
temperatures, and thermal acclimation in
Chondrus crispus
is characterized by
variations in antenna size rather than by reaction center densities (K
€
ubler and
Davison
1995
). Notably, not necessarily all components of the photosynthetic
apparatus are sensitive to a temperature change. Wilson et al. (
2003a
) describe that
shifting
C. vulgaris
cells from 5 to 27
C did not induce changes in the accumulation
of RuBisCO, a key enzyme of photosynthesis utilizing ATP and NADPH to reduce
CO
2
in the Calvin cycle. However, this result contradicts observations by Savitch
et al. (
1996
) and the amount of RuBisCO was also significantly higher in the kelp
Saccharina latissima
when grown at 5
C compared to 17
C-grown algae (Machalek
et al.
1996
). Acclimation of photosynthesis to high temperatures primarily involves
changes in lipid composition of thylakoid membranes and the adjustment of photo-
system II thermostability, which could be enhanced either directly through confor-
mational changes of the photosystem or indirectly via a carotenoid-dependent
modulation of membrane fluidity (Havaux and Tardy
1996
).
It appears that there is more than one cellular signaling mechanism involved in
temperature acclimation. There is consensus that the redox state of the plastoqui-
none pool acts as a sensor of imbalances in the electron transport and is involved in
regulating the gene expression of a large number of genes required for photosyn-
thesis (Pfannschmidt et al.
1999
). In addition, the
trans
-thylakoid pH gradient,
biosynthetic precursors of chlorophyll acting as potential signaling molecules, and
reactive oxygen species (see also Chap.
6
by Bischof and Rautenberger) acting as
second messenger type molecules have also been shown to be involved (Wilson and
Huner
2000
; Wilson et al.
2003b
). The response of thermal acclimation of photo-
synthesis appears to be highly comparable to that described for photoacclimation
(Huner et al.
1998
). However, temperature and light have been shown to have
interactive effects on photosynthesis and its regulation (Savitch et al.
1996
; Gray
et al.
1997
).
Today molecular tools such as cDNA and oligonucleotide DNA microarrays
(“gene chips”) are used for examining environmentally induced changes in the
transcriptome. Insights into the role of phenotypic plasticity in transcriptional
processes are beginning to be achieved in a variety of species, including Antarctic
fishes and invertebrates (Hofmann et al.
2000
; Clark and Peck
2009
). One major
obstacle to studies in seaweeds has been the lack of genomic information, which is
now increasing. The genome of the brown macroalga
Ectocarpus siliculosus
has
been sequenced by the French sequencing center Genoscope (see
http://www.cns.fr
)
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