Liquenes

Planta (2007) 226:1287–1297 DOI 10.1007/s00425-007-0563-6

O R I G I N A L A R T I CL E

Metabolic processes sustaining the reviviscence of lichen Xanthoria elegans (Link) in high mountain environments
Serge Aubert · Christine Juge · Anne-Marie Boisson · Elisabeth Gout · Richard Bligny

Received: 14 February 2007 / Accepted: 25 May 2007 / Published online: 16 June 2007 © Springer-Verlag2007

Abstract To survive in high mountain environments lichens must adapt themselves to alternating periods of desiccation and hydration. Respiration and photosynthesis of the foliaceous lichen, Xanthoria elegans, in the dehydrated state were below the threshold of CO2-detection by infrared gas analysis. Following hydration, respiration totally recovered within seconds and photosynthesis withinminutes. In order to identify metabolic processes that may contribute to the quick and eYcient reactivation of lichen physiological processes, we analysed the metabolite proWle of lichen thalli step by step during hydration/dehydration cycles, using 31P- and 13C-NMR. It appeared that the recovery of respiration was prepared during dehydration by the accumulation of a reserve of gluconate 6-P(glcn-6-P) and by the preservation of nucleotide pools, whereas glycolytic and photosynthetic intermediates like glucose 6-P and ribulose 1,5-diphosphate were absent. The large pools of polyols present in both X. elegans photo- and mycobiont are likely to contribute to the protection of cell constituents like nucleotides, proteins, and membrane lipids, and to preserve the integrity of intracellularstructures during desiccation. Our data indicate that glcn-6-P accumulated due to activation of the oxidative pentose phosphate pathway, in

response to a need for reducing power (NADPH) during the dehydration-triggered down-regulation of cell metabolism. On the contrary, glcn-6-P was metabolised immediately after hydration, supplying respiration with substrates during the replenishment of pools ofglycolytic and photosynthetic intermediates. Finally, the high net photosynthetic activity of wet X. elegans thalli at low temperature may help this alpine lichen to take advantage of brief hydration opportunities such as ice melting, thus favouring its growth in harsh high mountain climates. Keywords Energy metabolism · Lichens · Metabolic proWling · NMR spectroscopy · Reviviscence · Xanthoriaelegans Abbreviation CDTA 1,2-Cyclohexylenedinitrilotetraacetic acid Glcn-6-P Gluconate 6-P GPG Glycerophosphoglycerol GPC Glycerophosphocholine PCA Perchloric acid

Introduction
S. Aubert (&) · C. Juge · R. Bligny Station Alpine Joseph Fourier, UMS 2925 UJF CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble cedex 9, France e-mail: serge.aubert@ujf-grenoble.fr A.-M. Boisson · E. Gout · R.Bligny Laboratoire de Physiologie Cellulaire Végétale, Unité Mixte de Recherche 5168, Institut de Recherche en Technologies et Sciences pour le Vivant, CEA, 17 rue des Martyrs, 38054 Grenoble cedex 9, France

Lichens are among the most resistant of living organisms. They survive in extreme environments including the deserts and frigid areas of all Wve continents. In the alpine environment, thesesymbiotic organisms are exposed to harsh Xuctuations in water supply, light intensity, and temperature (Kappen 1988; Körner 2003). Xanthoria elegans (Link), used in this study, is a lichen typical of this habitat, whose growth on rocky surfaces mainly depends on atmospheric water inputs. X. elegans is a saxicolous desiccation-tolerant lichen of the Teloschistaceae family (Helms 2003),

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Planta (2007) 226:1287–1297

containing an ascomycetous fungus and a unicellular green alga belonging to the Teloschistes and Trebouxia genera, respectively (Helms 2003). At the site where they were harvested thalli naturally undergo hydration/dehydration cycles, growing when they are hydrated by melting snow, rain, or dew. Metabolic activity of lichen thalli, apparent as gas exchange,...