Effects of ultraviolet radiation on photosynthesis and related enzyme reactions of marine macroalgae

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 UV radiation. Maximal quantum yield of photochemistry (F v/Fm) and maximal electron transport rate (ETRmax) were measured with a pul se-amplitude-modulated fluorometer; the activity of the Calvin cycle enzyme s ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and glyceraldeh yde-3-phosphate dehydrogenase (G3PDH) were estimated using a photometric te st. Proteins of crude extracts were separated by SDS gel electrophoresis an d changes in cellular concentrations of Rubisco were determined, Moreover, the concentration of chlorophyll a (Chl a), and protein content, were measu red photometrically. In all species, Chl a content, maximal quantum yield a s well as ETRmax decreased during the UV treatment. Changes in ETRmax were related to the changes in the overall activity of Rubisco. Analysis of SDS gels showed that in P. rubens, L. solidungula, M. arcticum and A. esculenta decreasing Rubisco activity partly resulted from a degradation of the enzy me. However, in A. esculenta, the formation of a high-molecular-weight poly peptide was observed. In all species, the activity of Rubisco was more stro ngly 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 dif ferent sensitivities to UV exposure of the species tested reflect their zon ation pattern in the field.