Photosynthesis and relative amounts of photosynthetic proteins (D1, PsaA and Rubisco) in marine and brackish water ecotypes of Fucus vesiculosus and Fucus radicans (Phaeophyceae) :  Photosynthesis and proteins in Fucus

• This study investigated if the photosynthetic maximum capacity (Pmax) is related to the relative amounts of D1 (PsbA), PsaA proteins and ribulose-1.5-bisphosphate carboxylase/ oxygenase (Rubisco) in the marine, Norwegian Sea (34-35 practical salinity units, psu) and the brackish, Bothnian Sea (4-5 psu) ecotypes of Fucus vesiculosus and in Fucus radicans. The results revealed higher Pmax in the marine ecotype of F. vesiculosus compared to the brackish Fucus species. The relative amounts of PsaA proteins or D1/PsaA (photosystem II/photosystem I; PSII/PSI) ratio did not indicate any differences between the Fucus strains whereas the relative amount of D1 was higher in the marine F. vesiculosus compared to F. radicans. The PSII/PSI ratios confirm an overweight of PSI in all three Fucus strains. The analyses of the relative amount of Rubisco indicated a greater amount in both ecotypes of F. vesiculosus compared to F. radicans, whereas no differences could be detected between the two ecotypes of F. vesiculosus. Therefore, we suggest that the amount of Rubisco contributed to the differences of Pmax between the marine ecotype of F. vesiculosus and F. radicans. The lower Pmax in the brackish ecotype of F. vesiculosus compared to the marine ecotype however must have another origin and we suggest further investigations of the CO2 fixation rate of Rubisco. The study also included an investigation of the effects of salinity on Pmax and the relative amount of D1, PsaA and Rubisco in the brackish ecotype of F. vesiculosus. Treatment of the algae for one week in 5, 10, 20 and 35 psu resulted in a higher Pmax at higher salinities and a maximum at 10 psu. These results were not reflected in the amount of D1 or Rubisco whereas analyses of the amount of PsaA revealed the highest amount of PsaA in algae treated in 10 psu. We suggest a need of more ATP by cyclic ATP formation to supply a greater Rubisco activity as an explanation.  

Nyckelord

D1

Fucus vesiculosus

Fucus radicans

oxygen evolution

photosynthetic maximum capacity (Pmax)

protein

PSI

PSII

PsaA

Rubisco

salinity

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