Biology Reference
In-Depth Information
(L
uning 1990 ). Short-day responses of Laminaria hyperborea and Constantinea
subulifera result in the initiation of a new blade in the autumn or winter while the
rate of growth of the young blades of a kelp species ( Pleurophycus gardneri )is
stimulated by long-day conditions (Dring 1988 ). In contrast, photoperiodism in
unicellular algae is unknown and seasonal behavior shall be governed by ecological
factors, such as temperature, irradiance and nutrient levels (Luning 1990 ).
1.7 Conclusive Remarks
Distribution of marine macrophytes in deep water with low light depends mainly on
the minimal energy input. The annual fluence or minimum light level occurring in
the respective depth for maintenance of existing plant material must have a surplus
for growth and reproduction. During winter seasons algae in low light habitats have
to live for long periods each year at photon fluence rates which do not cover their
energy needs so that the energy must be chemically stored in the bright light
seasons. As light saturation of growth is fortunately lower than those for photo-
synthesis, deep water algae can still produce enough reserve materials under
favorable light conditions. In contrast, at the water surface, irradiance can be too
high and the algae have to avoid photodamage by additional investment in proteins
and cellular components for protection. These algae exhibit strong and fast regula-
tion of photosynthesis and perform photoprotective mechanisms, i.e., harmless heat
dissipation.
However, light does not only serve as a source for energy in photoautotrophic
organisms, but is also an environmental signal for regulation and development,
inducing changes in photoperiodism (dependence on daylength), photomorpho-
genesis (dependence on spectral range) and phototropism. In these cases the signal
character of light is evident from the low light requirement to induce a reaction.
Special photoreceptors are the sensors in the signal chain, whereas the energy to
perform the respective reaction is mostly provided by photosynthesis and thus
channeled from the energy absorbed by photosynthetic pigments. The variety of
the sensors and their responses in algae seem to be more varied than those among
flowering plants.
References
Ahn TK, Avenson TJ, Ballottari M, Cheng YC, Niyogi KK, Bassi R, Fleming GR (2008)
Architecture of a charge-transfer state regulating light harvesting in a plant antenna protein.
Science 320:794-797
Arnold KE, Murray SN (1980) Relationships between irradiance and photosynthesis for marine
benthic green algae (Chlorophyta) of differing morphologies. J Exp Mar Biol Ecol 43:183-192
Aro EM, Virgin I, Andersson B (1993) Photoinhibition of photosystem II. Inactivation, protein
damage and turnover. Biochim Biophys Acta 1143:113-134
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