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1 December 2000 Protection of Photosystem II Against UV-A and UV-B Radiation in the Cyanobacterium Plectonema boryanum: The Role of Growth Temperature and Growth Irradiance
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Abstract

Plectonema boryanum UTEX 485 cells were grown at 29°C and 150 μmol m−2 s−1 photosynthetically active radiation (PAR) and exposed to PAR combined with ultraviolet-A radiation (UV-A) at 15°C. This induced a time-dependent inhibition of photosystem II (PSII) photochemistry measured as a decrease of the chlorophyll a fluorescence ratio, Fv/Fm, to 50% after 2 h of UV-A treatment compared to nontreated control cells. Exposure of the same cells to PAR combined with UV-A ultraviolet-B radiation (UV-B) caused only a 30% inhibition of PSII photochemistry relative to nontreated cells. In contrast, UV-A and UV-A UV-B irradiation of cells cultured at 15°C and 150 μmol m−2 s−1 had minimal effects on the Fv/Fm values. However, cells grown at 15°C and lower PAR irradiance (6 μmol m−2 s−1) exhibited similar inhibition patterns of PSII photochemistry as control cells. The decreased sensitivity of PSII photochemistry of P. boryanum grown at 15°C and 150 μmol m−2 s−1 to subsequent exposure to UV radiation relative to either control cells or cells grown at low temperature but low irradiance was correlated with the following: (1) a reduced efficiency of energy transfer to PSII reaction centers; (2) higher levels of a carotenoid tentatively identified as myxoxanthophyll; (3) the accumulation of scytonemin and mycosporine amino acids; and (4) the accumulation of ATP-dependent caseinolytic proteases. Thus, acclimation of P. boryanum at low temperature and moderate irradiance appears to confer significant resistance to UV-induced photoinhibition of PSII. The role of excitation pressure in the induction of this resistance to UV radiation is discussed.

Alexander G. Ivanov, Ewa Miskiewicz, Adrian K. Clarke, Bruce M. Greenberg, and Norman P. A. Huner "Protection of Photosystem II Against UV-A and UV-B Radiation in the Cyanobacterium Plectonema boryanum: The Role of Growth Temperature and Growth Irradiance," Photochemistry and Photobiology 72(6), 772-779, (1 December 2000). https://doi.org/10.1562/0031-8655(2000)072<0772:POPIAU>2.0.CO;2
Received: 7 July 2000; Accepted: 1 September 2000; Published: 1 December 2000
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