Abstract
One of the adaptations whereby phytoplankton can alleviate damage induced by ultraviolet radiation (280-400 nm) is the synthesis of mycosporine-like amino acids (MAAs). The synthesis of MAAs was studied after exposure of the Antarctic diatom Thalassiosira sp. isolated from Potter Cove (South Shetland Is., Antarctica) to 2 treatments with a solar simulator: surface (Sfix) and vertical mixing (Mix) irradiance conditions. Light exposure was simulated in daily cycles with maximum irradiance at noon. Only 2 MAAs, Porphyra-334 (82-85%) and Shinorine (15-18%), were identified. The concentration of the two compounds increased during experimental light exposure (50-55%) and declined in the dark (10-15%). During the light period the synthesis rate of MAAs per unit of chlorophyll a was higher in the Sfix treatment (µ=0.17 h -1 ) than in the Mix treatment (µ=0.05 h -1 ). In spite of the higher MAA levels, low cell numbers were observed in the Sfix treatment, suggesting that the algae synthesized photoprotective compounds at the expense of growth. Our results document overlapping effects of both daily light cycles and vertical mixing affecting the synthesis of MAAs. This, and the high thermal dissipation of the ultraviolet B radiation energy (280-320 nm) absorbed by these substances, suggest a rapid photoadaptive response of Thalasiossira sp. upon exposure to elevated irradiance in a stratified water column, as well as the complementary role of vertical mixing in photo-protection.
Highlights
UV-absorbing compounds, especially mycosporinelike amino acids (MAAs), strongly absorb ultraviolet radiation (UVR, 280-400 nm) in phytoplankton and macroalgae (Carreto et al 1990a, Karsten et al 1999; Shick et al 1996)
SUMMARY: One of the adaptations whereby phytoplankton can alleviate damage induced by ultraviolet radiation (280-400 nm) is the synthesis of mycosporine-like amino acids (MAAs)
The synthesis of MAAs was studied after exposure of the Antarctic diatom Thalassiosira sp. isolated from Potter Cove (South Shetland Is., Antarctica) to 2 treatments with a solar simulator: surface (Sfix) and vertical mixing (Mix) irradiance conditions
Summary
UV-absorbing compounds, especially mycosporinelike amino acids (MAAs), strongly absorb ultraviolet radiation (UVR, 280-400 nm) in phytoplankton and macroalgae (Carreto et al 1990a, Karsten et al 1999; Shick et al 1996). Cullen and Lesser (1991), Neale et al (1998b) and Hernando and Ferreyra (2005) suggested that the impact of solar radiation on Antarctic phytoplankton in the upper metres of the water column in the euphotic zone is significantly modulated by vertical mixing. Both the degree of exposure to UVBR and the balance between damage and repair are a function of mixing depth and mixing speed (Neale et al 1998b). Mixing in water column is a key factor to be considered in evaluating MAA induction patterns (Ivanov et al 2000, MacDonald et al 2003)
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