Relative effects of nitrogen or phosphorus depletion and light intensity on the pigmentation, chemical composition, and volume of Pyrenomonas salina (Cryptophyceae)

Abstract

The nitrogen-rich phycobiliproteins are efficient light-harvesting pigments of cryptophytes, cyanobacteria, and rhodophytes. Whereas it is well established that certain cyanobacteria mobilize their phycobiliproteins in response to nitrogen deprivation, the effect of nitrogen stress on cryptophyte physiology has been studied only rarely. We compared the effects of nitrogen and phosphorus depletion on the biovolume, chemical composition, and pigment composition of the marine cryptophyte Pyrenomonas salina, grown in batch cultures under light-limiting and light-saturating conditions. Cellular phycoerythrin content declined during the late exponential growth phase in nitrogen-depleted cultures, and the cells were nearly devoid of phycoerythrin (< 3 % of the phycoerythrin content of nitrogen-replete cells) at the beginning of stationary growth. Phycoerythrin content also decreased during late exponential phase in phosphorus-depleted cultures, but these latter cells contained more than 10 times the phycoerythrin concentration of nitrogen-depleted cells at the same growth stage. Chlorophyll a content declined in nitrogen-depleted cultures, but at a slower rate than the decrease in phycoerythrin, such that the phycoerythrin to chlorophyll a ratio decreased by more than 95 O/O from the early exponential to early stationary growth phase. In nitrogen-depleted cultures grown at a low light intensity, the decline in phycoerythrin content preceded the decline in chlorophyll a content, and resulted in only slight changes in cellular nitrogen content and biovolume. These data indicate that phycoerythrin is preferentially lost from P. salina during nitrogen deficiency, and support the hypothesis that, similar to certain cyanobacteria, P. salina responds to nitrogen deprivation by mobilizing phycoerythrin in order to help sustain cellular nitrogen requirements.