Cyanobacteria must cope with the negative effects of ultraviolet B (280–315 nm) (UV-B) stress caused by their obligatory light requirement for photosynthesis. The adaptation of the cyanobacterium Anabaena sp. to moderate UV-B radiation has been observed after 2 weeks of irradiation, as indicated by decreased oxidative stress, decreased damage, recovered photosynthetic efficiency and increased survival. Oxidative stress in the form of UV-B–induced production of reactive oxygen species was measured in vivo with the oxidative stress–sensitive probe 2′,7′-dichlorodihydrofluorescein diacetate. Photooxidative damage by UV-B radiation, including lipid peroxidation and DNA strand breakage, was determined by a modified method using thiobarbituric acid reactive substances and fluorometric analysis of DNA unwinding. Photosynthetic quantum yield was determined by pulse amplitude–modulated fluorometry. The results suggest that moderate UV-B radiation results in an evident oxidative stress, enhanced lipid peroxidation, increased DNA strand breaks, elevated chlorophyll bleaching as well as decreased photosynthetic efficiency and survival during the initial exposure. However, DNA strand breaks, photosynthetic parameters and chlorophyll bleaching returned to their unirradiated levels after 4–7 days of irradiation. Oxidative stress and lipid peroxidation appeared to respond later because decreases were observed after 7 days of radiation. The survival curve against irradiation time exhibited a close relationship with the changes in photosynthetic quantum yield and DNA damage, with little mortality after 4 days. Growth inhibition by UV-B radiation was observed during the first 7 days of radiation, whereas normal growth resumed even under UV-B stress thereafter. An efficient defense system was assumed to come into play to repair photosynthetic and DNA damage and induce the de novo synthesis of UV-sensitive proteins and lipids, allowing the organisms to adapt to UV-B stress successfully and survive as well as grow. No induction of mycosporine-like amino acids (MAA) was observed during the adaptation of Anabaena sp. to UV-B stress in our work. The adaptation of the cyanobacterium correlated with and could be caused by the oxidative stress and oxidative damage.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 76 • No. 2