Paolo Modenesi

Determinant factors for the formation of the calcium oxalate minerals, weddellite and whewellite, on the surface of foliose lichens

The factors influencing the predominance of one of the two mineral forms of calcium oxalate (CO), the monohydrated whewellite (COM) and the di-hydrated weddellite (COD), forming the pruina of the upper cortex of lichens, have been investigated through a simple, sensitive histochemical assay: toluidine blue O (TBO), a metachromatic staining test. The differential reactivity of 43 thalli of 17 pruinose foliose species, supplemented by X-ray diffraction analysis and observations with polarizing and scanning electron microscopy, suggests that the histochemical reactivity of hyphal walls and cementing substances of the upper cortex are related to the density of anionic charges. These factors are probably due to the occurrence of polyuronic acid substances that strongly affects the mineralization of CO. Di-hydrated wedellite is always associated with TBO metachromatic reactivity, and COM with orthochromatic reactivity. When the material has an ambiguous ortho/metachromatic reactivity, COD and COM may occur together. This study presents the first experimental evidence that in lichens CO biomineralization is at least partially biologically controlled.

Isidia ontogeny and its effect on the CO 2 gas exchanges of the epiphytic lichen Pseudevernia furfuracea (L.) Zopf

The development of isidia in thalli of Pseudevernia furfuracea from the Carnic Alps (North-eastern Italy), and the effects of these structures on CO2 gas exchanges were investigated. The ontogenetic events were studied by comparison of sections stained with different histochemical tests and SEM observations. A high cell turnover rate in both symbiotic partners is the first sign of isidium development, followed by an increased aplanosporogenesis of algae and growth of neighbouring medullary hyphae which become oriented upwards. Large nuclei and an intense cytoplasm activity characterize the mycobiont cells. The surface of very young isidia shows an irregular structure of spherical to ovoid protruding tips of perpendicular cortical hyphae, that are later organised in a pseudomeristematic area similar to that observed in the apex of growing lobes. CO2 gas exchange measurements carried out in the laboratory confirmed the high metabolic activity of isidia. At optimal water content and favourable light conditions, isolated isidia had rates of gross photosynthesis and dark respiration that were twice those of non-isidiate lobes. Isolated isidia also had a very low CO2 saturation point, probably because of their favourable surface/volume ratio, and a high light saturation, probably linked to their high content of photosynthetic pigments. The different roles played by isidia in the biology of Pseudevernia furfuracea, and particularly their rejuvenating effect on aged lobes, are discussed, and the presence of thalloconidia is briefly mentioned.

Biomonitoring of Trace Metals by Different species of Lichens (Parmelia) in North-West Italy

The concentrations of Cd, Cu, Mn, Ni, Pb, V, and Zn were measured in four different species of lichens (Parmelia caperata, P. pastillifera, P. saxatilis, P. sulcata) sampled in North-West Italy, in order to obtain maps showing metal distribution and the degree of deviation from background (natural) conditions. Significant differences among the species were found for Zn, Mn, Pb and V, suggesting that the combined use of mixed species in biomonitoring surveys can affect the interpretation of results. Results obtained for Parmelia caperata samples have been compared with background (natural) levels, and maps showing the distribution of each metal expressed as deviation from background levels have been obtained. Overall such maps show a medium to high alteration degree in the study area.

Oxidative stress and usnic acid content in Parmelia caperata and Parmelia soredians (Lichenes).

High light levels together with Paraquat treatment or exposure to pollutants (e.g. SO2) can cause oxidative stress in epiphytic lichens. In some cases, a significant increase in ascorbic acid and other antioxidant metabolites, sometimes occurring in lichens only, was observed. In this study, usnic acid was measured by HPLC in Parmelia caperata and Parmelia soredians thalli treated with Paraquat, a herbicide which transfers electrons from various transport systems to oxygen, producing O2*- superoxide radicals. In light, Paraquat acts by generating active oxygen species within the chloroplast, thus simulating the oxidative component of environmental stress. The significant increase in the usnic acid content measured in P. soredians thalli (+ 36.3%) is in line with the hypothesis that it has an antioxidant action, but it is in contrast to the limited increase measured in P. caperata thalli (+ 13.7%). These apparently contradictory results confirm those found in the literature, which attribute different functions to usnic acid depending on the lichen species considered and on whether they have other detoxifying substances in their thalli. These studies are of potential application-oriented interest in relation to research into new active principles to be used in the pharmaceutical, food and cosmetic fields and/or in environmental biomonitoring.

Rapid biodiversity assessment in lichen diversity surveys: implications for quality assurance

Rapid Biodiversity Assessments (RBAs) of lichen communities, obtained by means of simplified sampling lists based on morphospecies, showed good correlations with Lichen Diversity Values (LDVs), based on the complete identification of lichen species only when performed by operators with high levels of taxonomic knowledge. Furthermore, the use of highly simplified sampling lists did not lead to significant advantages in terms of time needed for field operations. This approach proved to be especially unreliable in high diversity ecological contexts where variation of morpho-structural composition within lichen communities is frequent (i.e. co-occurring crustose- and foliose-dominated communities); it may also lead to weak results if applied for conservation purposes. Hence, the use of simplified RBA sampling lists in lichen monitoring has to be carefully evaluated and, in any case, should be based on sound taxonomic knowledge on the part of those in charge of data collection. The proper assessment of descriptors of lichen abundance and/or frequency, however, strictly depends on the skill, taxonomic knowledge, and willingness to learn of the lichenologist-in-training.

Applicability of the lichen biodiversity method (L.B.) to a Mediterranean area (Liguria, nw Italy)

This study is part of the work aimed to standardise air quality biomonitoring methods in Italy. Some practical problems of the application of the lichen biodiversity (L.B.) method to a coastal area of the eastern Ligurian Riviera are analysed. In the first phase we studied the influence of variability on the parameters of the phorophytic substrata, on which we carried out the releves. We considered the inclinations and circumferences of the tree trunks, and the exposure and height from the ground of the sampling grid. In the second phase, the study deals with the influence of the great geomorphologic variability on the microclimate and epiphytic lichen vegetation. The L.B. values were considered in relation to versant exposure, height above sea level and distance from the coast. We have suggested the use of less restrictive parameters for the L.B. sampling protocol. Furthermore, the distribution of two of the principal types of epiphytic lichen vegetation of the area, Xanthorion and Parmelion, were analysed in relation to the microenvironmental conditions.

New histochemical techniques for the localization of metal ions in the lichen thallus

The localization of inorganic contaminants in lichens is an important step toward a better understanding of the accumulating capability and toxitolerance of species (Hauck et al . 2002). Different methods, such as sequential elution technique (Brown 1995; Tretiach et al . 1999), X-ray microanalysis (Hauck et al . 2002) and microscopic histochemistry (Garty & Theiss 1989), have been used.

Preliminary evidence for a cholinergic-like system in lichen morphogenesis

SummaryMembrane acetylcholinesterase activity is considered to be a marker for a cholinergic system. When temporarily expressed in differentiating cells other than the nervous or muscular ones, it may play a role in morphogenesis. In the lichenParmelia caperata (L.) Ach., acetylcholinesterase is histochemically localized mainly in the cell walls and/or membranes of both symbionts just where they proliferate and form well-organized propagation structures, the soredia. The enzyme activity is first detected in a few algae undergoing aplanosporogenesis and later in medullary hyphae that reach the dividing algae by elongating perpendicularly to the thallus surface. This histochemical pattern that is associated with algal proliferation and oriented hyphal growth is characteristic of early morphogenesis of the soredia; when fully differentiated, they consist of an inner dividing alga and an outer hyphal envelope, both showing cholinesterase activity. Substrate specificity and inhibitor sensitivity of the histochemical staining indicate an acetylcholinesterase-like activity. However, extracts of the thallus areas where soredia develop give four bands of cholinesterase activity on disc electrophoresis: the two cathodal bands have the characteristics of acetylcholinesterase, the others of pseudocholinesterase. One of the latter hydrolyses propionylthiocholine very rapidly. The findings suggest that in lichen symbiosis, a cholinergic-like system participates in regulating morphogenetic processes such as cell division, oriented tip growth and alga-fungus membrane interactions. Environmental stimuli, particularly light, might trigger the development of soredia by modulating the activity of the cholinergic mechanism.

Temporal trends (1981-2007) of trace and rare earth elements in the lichen Cetraria islandica (L.) Ach. from Italian herbaria.

Twenty-four herbarium specimens of Cetraria islandica collected in Italy from 1981 to 2007 were used for retrospective analysis. Cd, Ce, Cu, Fe, Gd, La, Mn, Ni, Pb, Sb, V, Y, and Zn concentrations were measured. Pb showed a negative temporal trend, linked to the ban of leaded fuel for vehicles. Pb showed a negative correlation with the distance of the sampling sites from a highway in the years before 1995 and no relationship after that year, corresponding to the Pb content reduction in gasoline. A significant trend towards increasing Mn concentrations over time also emerged, which deserves further investigations due to Mn toxicity. Cluster analysis showed a group of elements of anthropogenic origin, while rare earth elements formed a separated cluster of natural origin. Lichens from herbaria proved to be a valuable tool for reconstructing historical trends in trace element deposition, highlighting variations produced by human activities.

Biomonitoring urban air pollution using transplanted lichens: element concentrations across seasons

We investigated the bioaccumulation of selected trace elements in samples of the lichen Evernia prunastri (L.) Ach. transplanted across two seasons in the urban area of Genoa (NW Italy), which is heavily affected by traffic and industrial pollution. Total concentration of most elements did not exhibit differences between seasons, exceptions being Al and Na, higher in summer, and As, Cd, and Ti, higher in winter. Differences emerged in the initial concentrations of some elements in control samples, and this was accounted for by the use of exposed-to-control (EC) ratios, which allowed interpretation of changes in element concentrations. The study area resulted highly polluted, likely by particulate matter, as suggested also by the higher concentrations of airborne PM10 during winter months. Bioaccumulation of particulate matter seems to be affected by differences in rainfall regimes across seasons, since element solubilization and leaching due to precipitation may vary considerably.