Effects of UV–visible radiation on growth, photosynthesis, pigment accumulation and UV-absorbing compounds in the red macroalga Gracilaria cornea (Gracilariales, Rhodophyta)

Radiation induces different processes in photosynthetic organisms through photosynthetic pigments and photoreceptors. This study evaluated the performance of the red alga Gracilaria cornea cultivated under different radiation treatments. The objective was to identify responses associated with the treatments and mediated by photoreceptors. For this, G. cornea was exposed for 15 days to low fluence radiation of the ultraviolet (UV)-visible spectrum (red, green and blue light, and UV-A and UV-B radiation) combined with a high fluence radiation provided by a low-pressure sodium lamp (SOX), in order to saturate the photosynthesis. We measure the growth rate and other variables, such as photosynthesis estimated as chlorophyll a fluorescence, chlorophyll a, phycobiliproteins, carotenoids, mycosporine-like amino acids (MAAs), phenolic compounds, antioxidant capacity soluble proteins, and internal carbon and nitrogen content. The results showed that the UV radiation influenced the growth rates, as well as the accumulation of internal compounds (carotenoids: violaxanthin, antheraxanthin and zeaxanthin; MAA palythine; and phenolic compounds). As the treatments with UV radiation also had a peak of blue light, the presence of photoreceptors sensitive to these qualities of radiation (UV-A, UV-B and blue light) is suggested. In general, UV-A appears to induce some compounds without affecting growth, while UV-B seems to cause the accumulation of compounds at the expense of growth. The effect of light quality on growth and metabolism in G. cornea is compared to that in other species following similar experimental design.