Effects of UV radiation on optimum quantum yield and sunscreen contents in members of the genera Interfilum, Klebsormidium, Hormidiella and Entransia (Klebsormidiophyceae, Streptophyta)

Abstract

Many members of the Klebsormidiophyceae typically occur in terrestrial habitats where they are exposed to ultraviolet radiation (UVR). To evaluate the extent of tolerance to this waveband, 32 strains of the genera Entransia, Hormidiella, Interfilum and Klebsormidium were exposed to identical artificial UVR. The respective response patterns were determined in terms of optimum quantum yield of PSII as well as the capability to synthesize and accumulate mycosporine-like amino acids (MAAs) as sunscreens. After exposure to UVR most of the investigated isolates of Hormidiella, Interfilum and Klebsormidium exhibited only a moderate or no decrease in optimum quantum yield. In contrast, both isolates of Entransia showed strong photoinhibition. These photosynthetic activity data are well reflected in the biochemical capability to synthesize MAAs. With the exception of both Entransia strains, where not even traces of MAAs could be detected, all other isolates of Hormidiella, Interfilum and Klebsormidium accumulated UV-absorbing compounds after UVR exposure. While Interfilum and Klebsormidium contained the same putative MAA with an absorption maximum at 324 nm, Hormidiella attenuata showed another putative MAA with an absorption maximum at 325 nm. In addition, both compounds exhibited different retention times during HPLC analysis, suggesting their chemical structure must be different. All data indicated a generally high UVR tolerance in Hormidiella, Interfilum and Klebsormidium which explains well their aeroterrestrial lifestyle.