An Sem Study of Injury Symptoms in Parmotrema Reticulatum Treated With Paraquat or Growing in Sulphur Dioxide-Polluted Air

Abstract

The effect of Paraquat, a herbicide known to stimulate oxygen-centred free-radical production in green plants, is compared with visible injury symptoms due to air pollution in Parmotrema reticulatum, an SO2-sensitive lichen species. This is in order to verify the hypothesized SO2 toxicity mechanism via the generation of free radicals. A new SEM-visible symptom is described: the production of heavy crystalline deposition on the thallus surface in SO2-stressed and Paraquat-treated specimens. The examination of the crystalline deposition by X-ray diffraction, correlated with SEM studies, showed that it is calcium oxalate (weddellite).

An anatomical investigation of calcicolous endolithic lichens from the Trieste karst (NE Italy)

“…In our opinion, the absence of Ca-oxalate crystals in endolithic lichens agrees with the most recent hypotheses on the possible functions of Ca-oxalate in lichens, and with the peculiar biology of endolithic lichens. According to MoDENESI (1993), Ca-oxalate is produced by lichens in response to oxidative events, such as those induced by pollution, or by high light regimes that can be efficiently reduced by Ca -oxalate crystals deposited on the upper cortex (KAPPEN, 1988;RIKKlNEN, 1995). At least in some foliose species, however, Ca-oxalate crystals seem to play an important role as a low-costing structural material which increase the strength of the hyphal wall (MODENESI et al, 1997).…”

Hydrogen Sulphide and Epiphytic Lichen Vegetation: a Case Study on Mt. Amiata (Central Italy)

“…The symptoms observed in foliose and fruticose thalli growing near H 2 S sources are similar to those caused by SO 2 (see Richardson & Nieboer 1981;Modenesi 1993). For this reason, we hypothesized that SO 2 was emitted together with H 2 S or produced by oxidation along our transect, but this was not supported by the results of field measurements.…”

“…An alternative mechanism is that H 2 S, as already demonstrated for bisulphite, undergoes aerobic oxidation to sulphate within the thalli, with the concomitant production of free radicals, which are effective agents of metabolic damage (Asada & Kiso 1973;Pelser & Yang 1977). According to Modenesi (1993), however, such molecules should induce the production of Ca-oxalate on lichen thalli, but analyses by X-ray microdiffraction failed to detect this biomineralization product in specimens collected at the two extremes of the transect (D. Pinna, in litt. ).…”

Antiproliferative activity of lichen extracts on murine myeloma cells

“…Furthermore, the response to oxidative stress (e.g. high light influx, SO 2 pollution, paraquat treatment) in lichens can follow several routes, such as production of crystalline deposits of calcium oxalate (Modenesi 1993;Modenesi et al 1998), increased synthesis of ascorbic acid (Caviglia & Modenesi 1999), and usnic acid (Caviglia et al 2001). In X. parietina, the orange coloured cortical anthraquinone compound parietin synthesised by the mycobiont protects the lichen photobiont against oxidation by excessive solar radiation (Gauslaa & McEvoy 2005).…”