Effects of heavy metals on seudoevernia furfuracea (L.) Zopf exposed in urban site and in vitro.

The lichens are effective pollution bioindicators and bioaccumulators. There are few ultrastructural studies on the effects of the environment in lichens and performed only on field exposed samples, submitted to numerous injuries, lacking comparisons with in vitro experiments that could reduce the possible causes of alterations. The aim of this study was to compare the effects of heavy metals on in vitro treated Pseudevernia furfuracea with field-exposed lichen. Lichen bags were exposed in the area of Acerra (Southern Italy). P. furfuracea, a fruticose and epiphytic lichen, was collected from Mount Faito. Nylon mesh bags containing lichen thalli (0.75 g) were exposed for six months (from March to September 2001) in 8 urban sites and 3 sites on Mount Faito (control). Heavy metal content in exposed lichen was quantitatively measured by inductively coupled plasma-mass spectrometry (ICP-MS Elan 600 of Perkin Elmer Sciex). The metals found were As, Cd, Cr, Pb, V, Cu, Zn, Fe, Al, and Mn. The heavy metals present in the highest quantity (Cu, Zn and Cd) were used for in vitro tests in the concentration range found in exposed samples. Lichen thalli were in vitro exposed to Mohr medium with the addition of Zn 10-4 M and Cu and Cd at 10-5 M and to metal free Mohr medium (control) for 24 hrs. Samples from lichen bags and in vitro experiments were fixed, dehydrated, embedded and stained for Transmission Electron Microscopy as elsewhere reported (Basile et al., 1994). Ultrastructural alterations showed by both samples (in vitro and in field exposed) were compared. The effects of stress on both kinds of specimen are very similar. The chloroplasts showed a change in thylakoid arrangement and pyrenoid morphology. Pyrenoglobuli and cytoplasmic storage droplets increased in number. The algal cells frequently contained dark vacuolar bodies only occasionally seen in the control. In the mycobiont cells abnormal and strong vacuolisation occurred. The fungal vacuoles often contained dark accumulations never seen in the control. Concluding, both symbionts are affected by stress due to atmospheric pollution and by in vitro heavy metal stress, showing similar ultrastructural alterations.