Spiral breakage and photoinhibition of Arthrospira platensis (Cyanophyta) caused by accumulation of reactive oxygen species under solar radiation

Previous studies showed that exposure of Arthrospira spp. spirals to natural levels of solar radiation in the presence of UV radiation (UVR, 280–400nm) led to the breakage of its spiral structure. However, the underlying mechanisms have not yet been explored. Here, we showed that associated accumulation of reactive oxygen species (ROS) resulted in the spiral breakage by oxidizing the lipids of sheath or cell membrane in Arthospira platensis, and presence of UVR brought about higher accumulation level of the ROS. Activities of superoxide dismutase (SOD) and catalase (CAT) were inhibited by high levels of solar PAR, addition of UVR led to further inhibition of CAT activity. High levels of ROS also decreased the content of photosynthetic pigments, damaged photosystem II (PSII) and inhibited the photosynthesis and growth. It is concluded that both UV and high PAR levels could generate higher amounts of ROS, which decreased the photosynthetic performances and led to spiral breakage of A. platensis.