Differential Response to Moderate UV-B Irradiation of Two Heterocystous Cyanobacteria Isolated from a Temperate Ricefield

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 O 2 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.

Physiological responses and specific fatty acids composition of Microcystis aeruginosa exposed to total solar radiation and increased temperature

“…Furthermore, CAT activity had a significant decrease at 26 °C when cells were exposed at high UVBR irradiance. This result has been reported before [41,94] and inactivation of CAT due to UVBR is a consequence of photo inactivation and degradation [95] of the haem group in CAT. A high reactive species concentration (statistically not significant) was produced in cells exposed to UVAR at 26 °C with a high solar irradiance, with consequent increased lipid damage despite of an increased SOD activity.…”

“…In cyanobacteria, proteins [41] and DNA [42] are the primary targets for UVR exposure and reactive species generation. Further, photosynthesis inhibition [43,44] and morphological changes [43] will be generated.…”

Effects of Ultraviolet-B Radiation in Plant Physiology

“…Lipids: When exposed to UV-B, lipids undergo lipid peroxidation whether they are glycolipids, phospholipids, or unsaturated fatty acids. UV-B exposed phospholipids are sensitive to ROS in two sites: the unsaturated double bond between the carbon atoms and the ester bond between glycerol and fatty acids (Kramer et al 1991;Moorthy & Kathiresan 1998;Hollosy 2002;Bhandari & Sharma 2006;Noaman 2007;Pérez et al 2012;Ganapathy et al 2017;Wang et al 2017). Polyunsaturated fatty acids (PUFAs) in the membrane`s phospholipids are also sensitive to ROS; since hydroxyl radical and singlet oxygen can react with methylene groups of PUFA and form lipid peroxy radicals and hydroperoxide.…”

Potential cyanobacterial inoculants for rice described from a polyphasic approach

“…Commercially available standard ethylene was used for quantification. ARA was performed in 25 mL aliquots of cell suspensions placed in 60 mL vials incubated with acetylene for 4 h. Ethylene concentrations were determined in a Shimadzu HP 5890 gas chromatograph equipped with a Porapack N column (28) . Nitrogenase activities were expressed as U mg -1 total proteins -1 , where U was μmol ethylene min -1 .…”