Photosynthesis, pigment composition and antioxidant defences in the red alga Gracilariopsis tenuifrons (Gracilariales, Rhodophyta) under environmental stress

Gracilariopsis tenuifrons is a red alga living in the upper intertidal zone of Playa de Carmen (Quintana Roo, Mexico), where abiotic stressors occur over the year. A high antioxidant capacity has been previously demonstrated for G. tenuifrons from the Mexican Caribbean. In this study, we evaluated the photosynthetic activity, pigment composition and antioxidant activity of G. tenuifrons under different culture conditions. G. tenuifrons was submitted to different irradiance intensities (100 and 1,000 mu mol photons m(-2) s(-1)), UV-B radiation and two nitrogen treatments (enriched and non-enriched). An effective defence system against oxidative stress in G. tenuifrons was induced by UV-B radiation coupled with high photosynthetically active radiation (PAR) with an increase in chlorophyll a, carotenoids content and antioxidant activity (2,2-diphenyl-1-picrylhydrazyl (DPPH) and Folin-Ciocalteu antioxidant assays). Our study has confirmed the hypothesis that G. tenuifrons is a stress-tolerant tropical species, and its tolerance strongly depends on nitrogen availability in the medium.