Acclimation of photosynthesis and pigments to seasonally changing light conditions in the endemic Antarctic red macroalga Palmaria decipiens

The influence of seasonally fluctuating Antarctic daylengths on the photosy nthetic apparatus of Palmaria decipiens was studied in culture experiments. Maximal photosynthetic activity (ETRmax) and maximal quantum yield (Fv/Fm) , measured by in vivo chlorophyll fluorescence, and concentrations of pigme nts (phycobiliproteins and Chl a) were determined monthly. Fv/Fm remained c onstantly high between 0.62 and 0.67 during mid-autumn, winter and spring. ETRmax and pigment contents increased continuously in mid-autumn and winter and were highest in spring. A positive correlation between pigments and ET Rmax was found. In summer, ETRmax, Fv/Fm and pigment levels decreased to th eir lowest values. P. decipiens acclimated by increasing phycobilisome (PBS ) number and changing PBS structure, probably changing rod length and rod n umber. The data show that P. decipiens is efficiently adapted to the short period of favourable light conditions in the field. A photoperiodic control of pigment synthesis triggered by daylength is suggested.