Photosynthetic characteristics and UV stress tolerance of Antarctic seaweeds along the depth gradient

The photosynthetic characteristics through P-E curves and the effect of UV radiation on photosynthesis (measured as rapid adjustment of photochemistry, F (v)/F (m)) and DNA damage (as formation of CPDs) were studied in field specimens of green, red and brown algae collected from the eulittoral and sublittoral zone of Fildes Peninsula (King George Island, Antarctic). The content of phenolic compounds (phlorotannins) and the antioxidant activity were also studied in seven brown algae from 0 to 40 m depth. The results indicated that photosynthetic efficiency (alpha) was high and did not vary between different species and depths, while irradiances for saturation (E (k)) averaged 55 mu mol m(-2) s(-1) in subtidal and 120 mu mol m(-2) s(-1) in eulittoral species. The studied species exhibited notable short-term UV tolerance along the vertical zonation. In intertidal and shallow water species, decreases in F (v)/F (m) by UV radiation were between 0 and 18 %, while in sublittoral algae, decreases in F (v)/F (m) varied between 3 and 35 % relative to PAR treatment. In all species, recovery was high averaging 84-100 %. The formation of CPDs increased (15-150 %) under UV exposure, with the highest DNA damage found in some subtidal species. Phlorotannin content varied between 29 mg g(-1) DW in Ascoseira mirabilis from 8 m depth and 156 mg g(-1) DW in Desmarestia menziesii from 17 m depth. In general, phlorotannin concentrations were constitutively high in deeper sublittoral brown algae, which were correlated with higher antioxidant activities of algal extracts and low decreases in photosynthesis. UV radiation caused a strong decrease in phlorotannin content in the deep-water Himantothallus grandifolius, whereas in D. menziesii and Desmarestia anceps, induction of the synthesis of phlorotannins by UV radiation was observed. The antioxidant activity was in general less affected by UV radiation.