STUDENT ABSTRACTS - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 272

UV-B-induced oxidative stress and damage in the cyanobacterium Anab ana sp.
YU-YING HE, DONAT-P. HÄDER
Friedrich-Alexander-Universität, Institut für Botanik und Pharmazeutische Biologie,
Erlangen, Germany
The increased UV-B irradiance on Earth due to the depletion of stratospheric
ozone 1 is detrimental to all forms of life including cyanobacteria, the most ancient
photosynthetic organisms. Under UV-B stress, the leakage of electrons from the
photosynthetic electron transport chain to oxygen 2 , the photosensitization of
photosynthetic pigments such as chlorophylls, phycobiliproteins and quinones 3
enhances the formation of reactive oxygen species (ROS) and thus exert oxidative stress
and oxidative damage to biomolecules such as lipids, proteins and DNA. Here we report
the UV-B-induced oxidative stress and oxidative damage including lipid peroxidation
and DNA strand breaks in the cyanobacterium Anabaena sp. Protective effects of
ascorbic acid were also investigated.
UV-B-induced production of ROS was detected in vivo by using the ROS-
sensitive probe 2´,7´-dichlorodihydrofluorescein diacetate (DCFH-DA). Photooxidative
damages by UV-B radiation were determined. Thiobarbituric acid reactive substances
(TBARS) and fluorometric analysis of DNA unwinding (FADU) methods were adapted
to measure lipid peroxidation and DNA strand breaks in Anabaena sp. under UV-B
stress. Our results suggested that moderate UV-B radiation results in an increase of ROS
production, enhanced lipid peroxidation and DNA strand breaks and a decreased
survival. The addition of ascorbic acid, an antioxidant which can scavenge ROS either
directly or via the ascorbate-glutathione cycle, counteracted the UV-B effect with
respect to the ROS enhancement and protected the test organisms from oxidative stress
and the resultant lipid peroxidation as well as DNA strand breaks, which allowed better
survival under UV-B stress.
Acknowledgements. The work outlined here was financially supported by an
Alexander-von-Humboldt Research Fellowship to Y.-Y. He and the European Union
(DG XII, Environment programme, ENV4-CT97-0580) to D.-P. Häder.
References
1. Kerr JB, McElroy CT (1993) Evidence for large upward trends of ultraviolet-B radiation linked to ozone
depletion, Science 262: 1032-1034.
2. Jordan BR (1996) The effects of ultraviolet-B radiation on plants: a molecular perspective, Adv. Bot. Res.
22 , 97-162.
3. Franklin LA, Forster RM (1997) The changing irradiance environment: consequences for marine
macrophyte physiology, productivity and ecology, Eur. J. Phycol. 32: 207-232.