Metabolic changes of the red marine alga Gracilariopsis tenuifrons elicited by high PAR in laboratory

Although known, the photosynthetically active radiation (PAR) triggers responses that still deserve attention. Then, our study aims to investigate the photoresilience responses of Gracilariopsis tenuifrons (C.J. Bird and E.C. Oliveira) Fredericq and Hommersand and the metabolic changes related with NO levels to understand the connective physiological responses under high light exposure. This outcome was evaluated after exposing this red alga for a week, to PAR levels of 60 and 600 μmol photons m⁻² s⁻¹, in both day and night phases. Growth rate, CHN (carbon, hydrogen, and nitrogen) contents, photosynthetic pigments (phycoerythrin, phycocyanin, chlorophyll-a, and carotenoids), total soluble proteins (TSP), antioxidant capacity, and nitric oxide (NO) production were analyzed. High PAR promoted the dissociation and diminution of photosynthetic pigments, thickened cell walls, increased C and H levels and antioxidant activity, raised NO values, and attenuation of N levels. Phycobiliproteins together with nitrogen and carbon metabolisms, antioxidant activity, and remarkable NO action have played significant roles in the photoresilience, as well as light-stress responses in G. tenuifrons under high PAR.