Abstract
In cyanobacteria both photosynthesis and nitrogen fixation can be affected by UV radiation. Two of the most abundant heterocystous cyanobacteria isolates from a temperate ricefield in Uruguay belonging to Anabaena and Calothrix genus were exposed for 1 or 3 hours to UV-B dosis similar to those to which they are exposed in summer. Anabaena survival after 1 h of UV-B exposure was 10% whereas in Calothrix’s was 30%. Both the quantum yields of photosybtem II fluorescence and O2 photoevolution decreased with time of UV-B exposure for Calothrix and only till 1 h for Anabaena. Only the Calothrix strain presented phycoerithryn as antenna pigment and constitutive UV-B screening mycosporine like aminoacids. In the Anabaena strain, nitrogenase activity was drastically reduced with UV-B irradiation but in Calothrix was not affected. Proline content and lipid peroxidation increased after 3 hours of UV-B exposure only in Anabaena sp. The antioxidant enzyme activities evaluated followed different trends for both isolates, with an increase in superoxide dismutase activity in the Calothrix isolate. These results show that the two nitrogen-fixing cyanobacteria studied have different responses to UV-B radiation and that cyanobacteria diversity may be considered when selecting strains to be used as biofertilizers.
Highlights
The current trend in the decrease of stratospheric ozone from anthropogenic inputs of chlorinated fluorocarbons has caused an increase of ultraviolet-B radiation (UV-B, 290 - 320 nm) reaching the biosphere
The antioxidant enzyme activities evaluated followed different trends for both isolates, with an increase in superoxide dismutase activity in the Calothrix isolate. These results show that the two nitrogen-fixing cyanobacteria studied have different responses to UV-B radiation and that cyanobacteria diversity may be considered when selecting strains to be used as biofertilizers
BI22 after UV-B radiation were inhibited in a different trend
Summary
The current trend in the decrease of stratospheric ozone from anthropogenic inputs of chlorinated fluorocarbons has caused an increase of ultraviolet-B radiation (UV-B, 290 - 320 nm) reaching the biosphere. High doses of UV-A/B radiation can pass through the water column and have deleterious effects on aquatic systems [2]. UV-B radiation is the one that produces the most severe cellular damage due to its direct effects on DNA and proteins and indirectly by the reactive oxygen species (ROS) production [3]. Cyanobacteria comprise the biggest and most widely distributed group of photosynthetic prokaryotes. They absorb solar radiation to drive photosynthesis and nitrogen fixation in some cases, being exposed to high doses of UV radiation. Many cyanobacteria have developed mechanisms to prevent the toxic effects caused by UV. DNA damage repair mechanisms, accumulation of detoxifying and antioxidant enzymes or synthesis of UVprotectants compounds [4]
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