Effects of ultraviolet radiation on photosynthesis and related enzyme reactionsof marine macroalgaeKai Bischof, Dieter Hanelt, Christian WienckeFoundation Alfred Wegener Institute, Am Handelshafen 12, 27570 Bremerhaven, GermanyReceived: 4 October 1999 / Accepted: 15 February 2000Abstract. Changes in physiological parameters related to photosynthesis were studied in five macroalgal species from Spitsbergen(Monostroma arcticum, Laminaria solidungula, Alaria esculenta, Palmaria palmata, Phycodrys rubens) during a 72-h exposure to UVradiation. Maximal quantum yield of photochemistry (Fv/Fm) and maximal electron transport rate (ETRmax) were measured with apulse-amplitude-modulated fluorometer; the activity of the Calvin cycle enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) were estimated using a photometric test. Proteins of crude extracts were separatedby SDS gel electrophoresis and changes in cellular concentrations of Rubisco were determined. Moreover, the concentration of chlorophylla (Chl a), and protein content, were measured photometrically. In all species, Chl a content, maximal quantum yield as well as ETRmaxdecreased during the UV treatment. Changes in ETRmax were related to the changes in the overall activity of Rubisco. Analysis of SDS gelsshowed that in P. rubens, L. solidungula, M. arcticum and A. esculenta decreasing Rubisco activity partly resulted from a degradationof the enzyme. However, in A. esculenta, the formation of a high-molecular-weight polypeptide was observed. In all species, the activity ofRubisco was more strongly impaired than that of G3PDH. Exposure to UV resulted in loss of total protein only in the deepwater species L.solidungula and P. rubens. The different sensitivities to UV exposure of the species tested reflect their zonation pattern in the field.Key words: Macroalgae - Photosynthesis - Ribulose-1, 5-bisphosphate carboxylase/oxygenase - UV radiation