Message - 7th IAL Symposium

Lichen: from genome to ecosystem in a changing world
5I-O
(5I-O5) Submission ID: IAL0254-00001
WHY LICHENS ARE OZONE TOLERANT? A POSSIBLE EXPLANATION FROM CELL
TO SPECIES LEVEL
Tretiach M. 1 , Bertuzzi S. 1 , Candotto Carniel F. 1 , Davies L. 2 , Francini A. 3
1 Dipartimento di Scienze Della Vita, Università degli Studi di Trieste, Trieste, Italy
2 Centre for Environmental Policy, Imperial College London, London, United Kingdom
3 Dipartimento di Coltivazione E Difesa Delle Specie Legnose Giovanni Scaramuzzi, Università di Pisa, Pisa, Italy
Ozone (O 3 ) is an important component of global change, contributing to 20 th century warming. Tropospheric
O 3 is constantly increasing and will continue to rise in the absence of control measures. This pollutant has
direct, deleterious consequences on the terrestrial biosphere through the formation of Reactive Oxygen Species
(ROS), that are particularly aggressive against cell membranes, enzymes and DNA. The data concerning the
putative effects on lichens available so far are largely incomplete and rather problematic, due to differences in
treatment methods, concentrations and exposure techniques. A recent field study with lichen transplants suggests
that the key factor in modulating the ozone resistance of lichens is water availability, because daily rehydrated
thalli can efficaciously repair O 3 damage and replenish the reservoir of antioxidants, whereas dry thalli
suffer from the sum of two co-occurring stressors, desiccation and O 3 . In this work the effects of O 3 on three
epiphytic macrolichens with different ecology and resistance to airborne pollutants (Flavoparmelia caperata,
Parmotrema perlatum and Xanthoria parietina) and their isolated photobionts (three species of Trebouxia) were
verified by exposing thalli and axenic cultures in fumigation chambers and/or OTCs at different air humidity and
watering regimes. Chlorophyll a fluorescence emission, antioxidants (AsA, GSH) and activity of specific enzymes
(APX, CAT, DHAR, GR, POD, SOD) were measured in pre and post exposure samples, and again after 1-2 days
of recovery. Histochemical techniques were used to localize ROS at cellular level by confocal microscopy, and
ultrastructural modifications were studied by TEM. The results show that all the three lichens tolerate O 3 well,
whereas desiccation tolerance varies in accordance to the species-specific ecology. The ozone tolerance is justified
by the availability of a large pool of constitutive antioxidants that in a lichen are necessary to contrast the
oxidative burst associated with the frequent dehydration-rehydration cycles to which it is naturally subjected, and
oxidation occurring during the protracted desiccation.
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