Acclimation of photosynthesis and pigments during and after six months of darkness in Palmaria decipiens (Rhodophyta):: A study to simulate Antarctic winter sea ice cover

The influence of seasonally fluctuating photoperiods on the photosynthetic apparatus of Palmaria decipiens (Reinsch) Ricker was studied in a year-round culture experiment. The optimal quantum yield (F-v/F-m) and the maximal relative electron transport rate (ETRmax), measured by in vivo chl fluorescence and pigment content, were determined monthly. During darkness, an initial increase in pigment content was observed. After 3 months in darkness, ETRmax and F-v/F-m started to decrease considerably. After 4 months in darkness, degradation of the light-harvesting antennae, the phycobilisomes, began, and 1 month later the light harvesting complex I and/or the reaction centers of PSII and/or PSI degraded. Pigment content and photosynthetic performance were at their minimum at the end of the 6-month dark period. Within 24 h after re-illumination, P. decipiens started to accumulate chl a and to photosynthesize. The phycobiliprotein accumulation began after a time lag of about 7 days. Palmaria decipiens reached ETRmax values comparable with the values before darkness 7 days after re-illumination and maximal values after 30 days of re-illumination. Over the summer, P. decipiens reduced its photosynthetic performance and pigment content, probably to avoid photodamage caused by excess light energy. The data show that P. decipiens is able to adapt to the short period of favorable light conditions and to the darkness experienced in the field.