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UV-C tolerance of symbiotic Trebouxia sp. in the space-tested lichen species Rhizocarpon geographicum and Circinaria gyrosa: role of the hydration state and cortex/screening substances

Sánchez, Francisco Javier and Meeßen, Joachim and del Carmen Ruiz, M. and Sancho, Leopoldo G. and Ott, Sieglinde and Vílchez, Carlos and Horneck, Gerda and Sadowsky, Andres and de la Torre, Rosa (2013) UV-C tolerance of symbiotic Trebouxia sp. in the space-tested lichen species Rhizocarpon geographicum and Circinaria gyrosa: role of the hydration state and cortex/screening substances. International Journal of Astrobiology, 13 (1), pp. 1-18. Cambridge University Press. DOI: 10.1017/S147355041300027X. ISSN 1473-5504.

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Abstract

Many experiments were carried out in order to evaluate the survival capacity of extremotolerant lichens when facing harsh conditions, including those of outer space or of simulated Martian environment. For further progress, a deeper study on the physiological mechanisms is needed that confer the unexpected levels of resistance detected on these symbiotic organisms. In this work, the response of the lichenized green algae Trebouxia sp. (a predominant lichen photobiont) to increasing doses of UV-C radiation is studied. UV-C (one of the most lethal factors to be found in space together with vacuum and cosmic-ionizing radiation with high atomic number and energy (HZE) particles) has been applied in the present experiments up to a maximum dose analogue to 67 days in Low Earth Orbit (LEO). For that purpose we selected two extremotolerant and space-tested lichen species in which Trebouxia sp. is the photosynthetic partner: the crustose lichen Rhizocarpon geographicum and the fruticose lichen Circinaria gyrosa. In order to evaluate the effect of the physiological state of the lichen thallus (active when wet and dormant when dry) and of protective structures (cortex and photoprotective pigments) on the resistance of the photobiont to UV-C, four different experimental conditions were tested: (1) dry intact samples, (2) wet intact samples, (3) dry samples without cortex/acetone-rinsed and (4) wet samples without cortex/acetone-rinsed. After irradiation and a 72 hours period of recovery, the influence of UV-C on the two lichen’s photobiont under each experimental approach was assessed by two complimentary methods: (1) By determining the photosystem II (PSII) activity in three successive 24 hours intervals (Mini-PAMfluorometer) to investigate the overall state of the photosynthetic process and the resilience of Trebouxia sp. (2) By performing high performance liquid chromatography (HPLC)-quantification of four essential photosynthetic pigments (chlorophyll a, chlorophyll b, β-carotene and lutein) of one sample of each species and dose. Results indicate that the physiological state of the thallus is the most important factor impairing the tolerance of Trebouxia sp. to UV-C radiation in both lichen species. Desiccated thalli were demonstrated to be more resistant to UV-C. No clear influence of UV-C radiation on the carotenoid content was detected. Comparing the respective doses applied, the individuals of R. geographicum are more sensitive than C. gyrosa.

Document Type:Article
Title:UV-C tolerance of symbiotic Trebouxia sp. in the space-tested lichen species Rhizocarpon geographicum and Circinaria gyrosa: role of the hydration state and cortex/screening substances
Authors:
AuthorsInstitution or Email of Authors
Sánchez, Francisco JavierDepartamento de Observación de la Tierra, INTA – Instituto Nacional de Técnica Aeroespacial, Ctra. Ajalvir km. 4, Torrejón de Ardoz, 28850 Madrid, Spain, e-mail: sanchezifj@gmail.com
Meeßen, JoachimInstitute of Botany, Heinrich-Heine University, Universitätsstr.1, 40225 Düsseldorf, Germany
del Carmen Ruiz, M.International Centre for Environmental Research (CIECEM), Universidad de Huelva (UHU), Parque Dunar, Almonte, 21760 Huelva, Spain
Sancho, Leopoldo G.Departamento de Biología Vegetal II, Facultad de Farmacia, Universidad Complutense de Madrid (UCM), 28040 Madrid, Spain
Ott, SieglindeInstitute of Botany, Heinrich-Heine University, Universitätsstr.1, 40225 Düsseldorf, Germany
Vílchez, CarlosInternational Centre for Environmental Research (CIECEM), Universidad de Huelva (UHU), Parque Dunar, Almonte, 21760 Huelva, Spain
Horneck, GerdaGerman Aerospace Center (DLR), Institute of Aerospace Medicine, Radiation Biology Division, 51170 Cologne, Germany
Sadowsky, AndresInstitute of Botany, Heinrich-Heine University, Universitätsstr.1, 40225 Düsseldorf, Germany
de la Torre, RosaDepartamento de Observación de la Tierra, INTA – Instituto Nacional de Técnica Aeroespacial, Ctra. Ajalvir km. 4, Torrejón de Ardoz, 28850 Madrid, Spain
Date:2013
Journal or Publication Title:International Journal of Astrobiology
Refereed publication:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:13
DOI:10.1017/S147355041300027X
Page Range:pp. 1-18
Publisher:Cambridge University Press
ISSN:1473-5504
Status:Published
Keywords:Trebouxia sp., Rhizocarpon geographicum, Circinaria gyrosa, extremophile, UV-C radiation, Astrobiology
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Research under Space Conditions
DLR - Research area:Raumfahrt
DLR - Program:R FR - Forschung unter Weltraumbedingungen
DLR - Research theme (Project):R - Vorhaben Strahlenbiologie
Location: Köln-Porz
Institutes and Institutions:Institute of Aerospace Medicine > Radiation Biology
Deposited By: Kerstin Kopp
Deposited On:12 Sep 2013 13:59
Last Modified:08 Jan 2014 13:29

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