Message - 7th IAL Symposium

4B-O
Lichen: from genome to ecosystem in a changing world
(4B-O6) Submission ID: IAL0210-00001
DESICCATION TOLERANCE IN THE HYGROPHILOUS LICHEN PARMOTREMA PERLATUM
AND IN ITS ISOLATED TREBOUXIA PHOTOBIONT
Candotto Carniel F. 1 , Bertuzzi S. 1 , Francini A. 2 , Pellegrini E. 2 , Tretiach M. 1
1 Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Trieste, Italy
2 Dipartimento di Coltivazione e Difesa delle Specie Legnose Giovanni Scaramuzzi, Università di Pisa, Pisa, Italy
Desiccation is one of the most important sources of oxidative stress because it gives rise to the production
of a variety of Reactive Oxygen Species. ROS are highly reactive, damaging molecules like DNA, lipids
and proteins. In poikilohydrous autophototrophic organisms the production of ROS is further enhanced by light,
because chlorophylls, although partially protected by structural changes at cortical and photosystem level, extinguish
excitation energy not only through heat emission, but also through the direct transfer of electrons to the
triplet oxygen, giving rise to the highly reactive singlet oxygen. In this study the role of light during a protracted
desiccation period on the ROS production and antioxidant response was investigated. Lobes of the lichen Parmotrema
perlatum and axenic cultures of the photobiont (a species of Trebouxia, putatively T. crenulata) were
treated at different light intensities (0, 40, 120 μmol photons m -2 s -1 ) for two weeks in a desiccated state. Concentrations
of H 2 O 2 , SOD, GSH and GSSG were measured spectrophotometrically, and a series of confocal laser
scanning microscope (CLSM) acquisitions were taken, using diclorofluorescein as a marker of the presence of
H 2 O 2 . After the light treatments the lobes and the cultures were kept fully hydrated at 20 μmol photons m -2 s -1
for three days to verify whether they were able to fully scavenge the accumulated ROS and to reconstitute their
original pool of antioxidants. The biochemical assays showed that concentrations of H 2 O 2 changed according
to the light treatments in both lobes and axenic cultures and CLSM acquisitions revealed a similar pattern. Accumulation
of ROS was mostly citoplasmatic and was particularly intense at photobiont and cortical level. The
comparison between lichenized and isolated Trebouxia based on chlorophyll a fluorescence emission revealed
that the former tolerates better the desiccation stress.
(4B-O7) Submission ID: IAL0195-00001
PHOTOSYNTHESIS, N FIXATION AND NUTRIENT CONTENT IN THREE SPECIES
OF PLACOPSIS FROM A SUBANTARCTIC ENVIRONMENT
Raggio Quilez J. 1 , Crittenden P. D. 2 , Green T. 1 , Pintado A. 1 , Vivas M. 1 , Sancho L. 1
1 Biología Vegetal II, Complutense University, Madrid, Madrid, Spain
2 School of Biology, University of Nottingham, Nottingham, United Kingdom
Placopsis is a genus of tripartite crustose lichens and has its main distribution in the Southern Hemisphere.
A common feature of all the species in the genus is the presence of cyanobacteria arranged in specialized
structures called cephalodia, in which nitrogen can be fixed from atmosphere. It has been suggested that
this nitrogen fixing capacity allows the genus to colonize barren nutrient poor habitats such as terrain recently
exposed following glacial retreat. Some of species of Placopsis have been used for dating exposed surfaces
using the technique of lichenometry. However, there are few physiological data for Placopsis sp., and little is
known about their growth dynamics. We have studied three species in the genus (the soil/mud inhabiting P.
pycnotheca, and the epilithic P. perrugosa and P. stenophylla) growing in the proximity of Pia Glacier, Beagle
Channel, Tierra del Fuego, Southern Chile. We report the results of novel investigations in Placopsis into the
relationships between CO 2 exchange, nitrogen fixation and total nitrogen and phosphorus content and show how
these parameters are related to individual species performance. Our laboratory results suggest: (i) a strong relationship
between the gas exchange data obtained and the two different ecologies of the species in the field and
(ii) positive correlations between CO 2 exchange, nitrogen fixation and nutrient content. These results improve
understanding of physiological interactions between the partners of tripartite lichens.
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