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Applied and Environmental Microbiology, April 2005, p. 2121-2129, Vol. 71, No. 4
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.4.2121-2129.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Rehydration of the Lichen Ramalina lacera Results in Production of Reactive Oxygen Species and Nitric Oxide and a Decrease in Antioxidants

Lior Weissman,¹ Jacob Garty,^1,2 and Ayala Hochman^3*

Department of Plant Sciences,¹ Institute for Nature Conservation Research,² Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel³

Received 28 October 2004/ Accepted 1 November 2004

Lichens are slow-growing associations of fungi and unicellular green algae or cyanobacteria. They are poikilohydric organisms whose lifestyle in many cases consists of alternating periods of desiccation, with low metabolic activity, and hydration, which induces increase in their metabolism. Lichens have apparently adapted to such extreme transitions between desiccation and rehydration, but the mechanisms that govern these adaptations are still poorly understood. In this study, the effect of rehydration on the production of reactive oxygen species and nitric oxide as well as low-molecular-weight antioxidants was investigated with the lichen Ramalina lacera. Rehydration of R. lacera resulted in the initiation of and a rapid increase in photosynthetic activity. Recovery of photosynthesis was accompanied by bursts of intracellular production of reactive oxygen species and nitric oxide. Laser-scanning confocal microscopy using dichlorofluorescein fluorescence revealed that formation of reactive oxygen species following rehydration was associated with both symbiotic partners of the lichen. The rate and extent of reactive oxygen species production were similar in the light and in the dark, suggesting a minor contribution of photosynthesis. Diaminofluorescein fluorescence, indicating nitric oxide formation, was detected only in fungal hyphae. Activities associated with rehydration did not have a deleterious effect on membrane integrity as assessed by measurement of electrolyte leakage, but water-soluble low-molecular-weight antioxidants decreased significantly.

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* Corresponding author. Mailing address: Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel. Phone: 972-3-6409886. Fax: 972-3-6406834. E-mail: ayalah{at}tauex.tau.ac.il.

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Applied and Environmental Microbiology, April 2005, p. 2121-2129, Vol. 71, No. 4
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.4.2121-2129.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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• Weissman, L., Garty, J., Hochman, A. (2005). Characterization of Enzymatic Antioxidants in the Lichen Ramalina lacera and Their Response to Rehydration. Appl. Environ. Microbiol. 71: 6508-6514 [Abstract] [Full Text]