Accumulation of zinc by the brown alga Padina gymnospora

Recently high zinc concentrations have been observed in Padina gymnospora (Kutzing) Vickers (Phaeophyta) in Sepetiba Bay, an area located on the Southeastern Brazilian coast. The environment of Sepetiba Bay is strongly influenced by large emissions of contaminants from a nearby industrial park. To evaluate the capability to accumulate zinc, individuals of this species were collected in a non-polluted area and experiments were conducted under a controlled situation. Young plants were exposed to 10, 100 and 1000 μg.l -1 Zn for 4 days. No significant effect on growth was observed at all tested concentrations. The level of zinc in the thalli contaminated with 10 μg.l -1 was about 100 μg.g -1 (dry wt), while the average levels found in algae collected in the field varied from 16 to 20 μg Zn.g -1 of dry wt. The levels of zinc at the concentrations of 100 and 1000 μg.l -1 were respectively 643 and 3764 μg.g -1 (dry wt) in the apical regions, and 289 and 1725 μg.g -1 (dry wt) in the basal regions of the thalli. In this study, electron spectroscopic images of cells treated with 1000 μg.l -1 were obtained with the Zeiss CEM 902 electron microscope, to study the location of zinc in cells. Numerous granules of zinc were observed along the both outer and inner cell walls. Very few Zn granules with very small diameters were observed inside the cells, bound to membranous structures. Their roles in the cell metabolism and ultrastructure are to be investigated.