Premium
Protection of Photosystem II Against UV‐A and UV‐B Radiation in the Cyanobacterium Plectonema boryanum : The Role of Growth Temperature and Growth Irradiance ¶
Author(s) -
Ivanov Alexander G.,
Miskiewicz Ewa,
Clarke Adrian K.,
Greenberg Bruce M.,
Huner Norman P. A.
Publication year - 2000
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2000)0720772popiau2.0.co2
Subject(s) - irradiance , photosystem ii , chemistry , radiation , photochemistry , cyanobacteria , ultraviolet radiation , photosynthesis , materials science , biophysics , optoelectronics , optics , biology , physics , biochemistry , bacteria , radiochemistry , genetics
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, F v /F m , 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 F v /F m 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.