Photoprotective function of mycosporine-like amino acids in a bipolar diatom (Porosira glacialis): evidence from ultraviolet radiation and stable isotope probing

This study investigated the synthesis of photoprotective compounds by Bacillariophyceae (Porosira glacialis) in real time using a 13C tracer. Our results show a relationship between the net production rates of mycosporine-like amino acids (MAAs) and photoprotective pigments such as diadinoxanthin (DD). After 24 h, the total carbon uptake rate of P. glacialis was higher when exposed to photosynthetically active radiation (PAR) than when exposed to ultraviolet radiation (UVR). However, with time, the total carbon uptake rate and turnover rate of P. glacialis exposed to UVR increased to the point where the net production rate of MAAs under UVR was higher than that of P. glacialis exposed to PAR. The differences in MAA and DD production rates and carbon uptake indicate the production of MAA and DD as a defense strategy in response to UV-induced damage. The results of this study provide insight into the synthetic pathways of photoprotective compounds and the carbon cycle within P. glacialis cells and reveal contrasting patterns in the production of MAAs and xanthophyll compounds such as DD over time.