Effects of heavy metals on protonemal development and ultrastructure in populations of the moss Funaria hygrometrica Hedw. (Bryophyta) from a mine and an unpolluted site

The effects of Pb and Zn on protonemal morphogenesis and ultrastructure were studied in two populations of the toxic-tolerant moss Funaria hygrometrica Hedw., one from a mining site with Pb and Zn pollution (A population) and the other from an unpolluted site (B population). Spores from the two populations were cultured in Mohr modified liquid medium either without heavy metals (control) or with the addition of both Pb and Zn nitrate 10 -5 M. The responses to heavy metals were evaluated on the basis of the following parameters: percentage of germination, protonemal growth, structural and ultrastructural changes. Under control conditions a high frequency of spore germination (90-95%) and comparable appearance of the protonemata from both A and B populations were shown. When grown in medium additionated with heavy metals, the protonemata from A population showed no severe alterations relative to the control; in contrast, the samples from B population showed severe alterations. The structural and morphogenetic alterations observed might reflect heavy-metal-induced disturbances in the microtubule cytoskeleton. In protonemata from A population X-ray TEM microanalysis revealed Pb and Zn essentially in vacuoles and cell wall, whereas these two elements were also detected in other cell compartments including plastids, and the nucleus in protonemata from B population. Cell wall and vacuolar compartmentation might account, at least in part, for the higher tolerance to heavy metals shown by the A population relative to B population.