Biology Reference
In-Depth Information
and no effect was found at a wavelength above 550 nm, as it is typical in a blue light
response (Flores-Moya et al.
2002
). In
Ectocarpus siliculosus
the waveband
between 430 and 450 nm was found to be the most effective for photoaccumulation
of the male gametes (M
uller et al.
1987
), also shown by the action spectrum of their
phototactic response (Kawai et al.
1990
). The action spectrum of the chloroplast
movement of the brown alga
Dictyota dichotoma
resembles the absorption spec-
trum of the blue light photoreceptor cryptochrom and serves as a control of the light
absorptance in brown seaweeds (Hanelt and Nultsch
1989
). In addition a blue light
receptor is also responsible for the egg release in
D. dichotoma
(Luning
1990
).
Phototrophic reactions have been observed, e.g., in the zygotes of
Fucales
, haptera
of
Laminariales
or rhizoids of kelps, and even more examples on light control are
given in the seaweed topic of L
€
uning (
1990
).
Circadian and circannual rhythms in algae are also controlled by light that time
metabolic, physiological and/or behavioral events to occur at optimal phases of the
daily or annual cycle. Eukaryotic algae serve for long time as model system to study
circadian rhythms. (Suzuki and Johnson
2001
). For example, UV shows the stron-
gest effect of destruction at sunset and the early night when UV levels are naturally
low and, hence, the control due to the daily clock enhances the fitness during the
day at higher UV levels (Nikaido and Johnson
2000
). Photoperiodic time
measurements, i.e., the detection of the lengths of day or night, is the ability to
sense the season of the year and to respond appropriately so as to adapt to seasonal
changes in the environment (L
€
uning and tom Dieck
1989
). The red Antarctic alga
Palmaria decipiens
shows a seasonal pattern of photosynthetic activity and pigment
synthesis (L
€
uder et al.
2001
; see also Chap.
13
Wiencke and Amsler). Maximal
electron transport rates of photosynthesis and pigment content increased in
P. decipiens
during mid-autumn and winter. Highest photosynthetic capacity and
size and number of phycobilisomes were observed in spring according to sea ice
break up so that photosynthetic performance was most effective during clear water
conditions. In summer the photosynthetic apparatus degrades and the life strategy
of the algae was defined as season anticipator (Luder et al.
2001
). This is contrary to
species (e.g.,
Iridaea cordata
or
Adenocystis utricularis
) where photosynthesis
and growth follow the seasonally increasing daylight period and are defined as
season responders with opportunistic life strategy. After an artificially prolonged
dark period of 6 months
P. decipiens
lost its ability to photosynthesize with
degradation of its light harvesting antennae, the phycobilisomes, and probably
through degradation of the reaction centers of photosystem II. Re-illumination
within 1 day induced fast accumulation of chlorophyll a and enables active photo-
synthesis, which indicates rapid repair mechanisms (L
€
uder et al.
2002
). This shows
how light controls the activity of the photosynthetic apparatus. The formation of
erect thalli in red and brown algae, from a prostrate system (a crust or branching
filaments), is commonly controlled by the photoperiod, and either gametogenesis or
sporogenesis may also occur in response to changes in daylength (Dring
1988
).
In spring the erect siphonous thallus of
Scytosiphon
and the folios thalli of the
green
Monostroma
appear in the cold temperate eulittoral zone, whereas they
survive the summer to winter month as crustaceous or respective
Codiolum
phase
€
