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Item Photoinhibition as a regulative mechanism of photosynthesis in marine algae of Antarctica(1994) Hanelt, Dieter; Jaramillo, Jorge; Nultsch, Wilhem; Senger, Sebastian; Westermeier, RenatoPhotosynthetic activity, photoinhibition and recovery of photosynthesis in the brown alga Adenocystis ultricularis and in the red alga Palmaria decipiens were studied infield experiments on King George Island (Antarctica) in February 1993. Experiments were carried out with a portable fluorometer and an oxygen-measuring device constructed especially for field studies. Both algal species show photoinhibition of photosynthesis observed influorescence and oxygen measurements during the course of a day. The kinetics of photoinhibition and recovery of photosynthesis were very fast at low water temperature albeit enzymatic reactions are involved in these processes. The brown alga A. utricularis reacts faster than brown macroalgae of the tropic and moderate latitudes. Thus, it may be questioned whether the turnover-cycle of the D1 -protein of photosystem II is involved in the molecular process of photoinhibition, unless the enzymatic processes involve in photoinhibition or recovery are adapted to low temperatures in the Antarctic species. A comparison of the reactivity to changing light conditions of the intertidal A. utricularis and P. decipiens with maximal growth rate in the subtidal zone shows that the brown intertidal alga responds to a strong light stress much faster and with a higher photoinhibitory degree as the red alga. In addition, recovery of the brown intertidal alga is much faster than the recovery of P. decipiens. This indicates that a relation between photoinhibition and zonation of these algae exists. Both algal species can cope with excessive light conditions as a results of photoinhibition. Thus, photoinhibition of photosynthesis is rather a regulatory mechanism than a photodamage in marine algae so that photosynthesis can acclimate to strong light conditions especially occuring when low tide concides with high irradiance around noon.