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green light for all red algae investigated. The action spectra of growth followed the
photosynthetic action spectra, with maximum efficiencies in the green wavebands,
corresponding to the wavelength distribution occurring in deep coastal waters. This
points to the importance of light quality for survival at low photon fluence rates and
corroborates the findings of Harder and Bederke (
1957
), Beer and Levy (
1983
) and
Glover et al. (
1986
,
1987
).
1.6 Light as an Environmental Signal
The color of light can induce photomorphogenetic effects, enzyme activity induc-
tion or controls the life cycle of the algae. Light is not only the primary energy
source but it also provides them with information to modulate developmental
processes such as phototaxis of swarmers, phototrophic reactions, chloroplast
movement, shade avoidance, circadian rhythms, etc. (L
uning
1990
; Kleine et al.
2007
). Plants can detect almost all facets of light, including direction, duration and
wavelength using three major classes of photoreceptors: the red/far-red light-
absorbing phytochromes which are only proven to be a sensor in green algae
(Dring
1988
;R
€
udiger and L´pez-Figueroa
1992
), the blue/UV-A light-absorbing
cryptochromes and phototropins, and UV-B-sensing UV-B receptors (Chen et al.
2004
). A phytochrome-like protein was described in all pigment groups of the
macroalgae; however, red/far-red forms were isolated only from green algae
(L
´
pez-Figueroa et al.
1989
,
1990
). Cryptochromes seem to be widespread in the
group of Phaeophyta and, possibly, among chromophyte algae in general (Dring
1988
). The photoreceptors perceive light signals and initiate intracellular signaling
pathways involving proteolytic degradation of signaling components and large
reorganization of the transcriptional program to modulate plant growth and devel-
opment (Chen et al.
2004
). Nitrate reductase activity in green algae and biliprotein
accumulation in some red algae may be stimulated by blue or green light, and an
interaction with phytochrome like photoreceptors was indicated (L´pez-Figueroa
and Rudiger
1991
;L´pez-Figueroa and Niell
1991
). Blue light, similar to low
light, induces an increase in the number of pigment systems per electron transfer
chain in green algae, whereas red light blocks chlorophyll b synthesis and leads to
a decreased light-harvesting system together with an increase in the number of
reaction centers per electron transfer chain (Senger et al.
2002
). The latter equates
an adaptation to strong light conditions. The opposite behavior of algae and higher
plants to red or blue light corresponds to the different spectral conditions in their
habitat. In deep water regions algae grow under blue light conditions whereas
higher plants are exposed to a higher fraction of red light. However, Senger et al.
(
2002
) come to the conclusion that the phylogenetic relationship is the major factor
for this difference in the light adaptation between algae and higher plants rather
than a long-term adaptation to the environment.
The phototactic response of swarmers of the brown algae
Scytosiphon
lomentaria
and
Petalonia fascia
causes a photoaccumulation at a peak of 450 nm,
€
