Effects of stressing high PAR on mycosporine-like amino acids in the red alga Gracilariopsis tenuifrons (Gracilariales, Rhodophyta)

Abstract

Studies in Rhodophyta species have been carried out to understand the mechanism of photoprotection against excessive photosynthetically active radiation (PAR). However, few studies concerning on the role of mycosporine-like amino acids (MAAs) in this mechanism have been developed. Thus, the aims of this study were to identify the MAAs in Gracilariopsis tenuifrons (C.J. and E.C Oliveira) Fredericq & Hommersand and understand the behavior of these compounds against the high PAR stress. To achieve these goals, apical tips of G. tenuifrons were cultivated at three PAR intensities (60, 600 and 1000µmol.m-2.s-1) for one week. The MAAs were identified and quantified by HPLC-MS and HPLC. Asterina-330, palythinol, palythene and usujirene were identified. Usujirene is an inedited MAA identified for this family and palythene is very unusual. Among these MAAs, only palythinol content increased about 3-fold in high light. This response may suggest that palythinol plays an important role in photoprotection in this alga. The role of MAAs in absorbing UV radiation and dissipate the excess of energy as harmless heat is well known. However, some of these compounds have been reported as PAR-dose dependent. Controversial results regarding palythinol amounts in red algae under high PAR intensities have been published. Although in Chondrus crispus (Gigartinales, Rhodophyta) this compound increased [1], in Palmaria palmata (Palmariales, Rhodophyta) it was reduced [2]. Since some MAAs could present antioxidant activity, this feature is suggested as the explanation for the mechanism of photoprotection. However, because there are conflicting results in the literature, the role of palythinol in photoprotection should be further investigated.