The results presented in this paper describe the short- and long-term toxicity of arsenate in Silene vulgaris. Short-term toxicity, measured as inhibition of root elongation, depended on phosphate nutrition, arsenate being much less toxic at high phosphate supply. At low phosphate levels more arsenic was taken up by the plants. Under chronic exposure, toxicity (measured as inhibition of biomass production) did not increase with time. In addition, the accumulation of phytochelatins (PCs) as a function of toxicity and duration of exposure was studied. Short-term PC accumulation (over a 3 d period) was positively correlated with exposure. Isolation of peptide complexes from prolongedly exposed plants showed that PC2, PC3 and PC4 were present, although the latter not until at least 3 d exposure. Arsenic co-eluted mainly with PC2 and PC3. Fractions containing PC4 were devoid of As, probably due to dissociation of the complexes during extraction or elution. The breakdown of PCs after arresting As exposure was very slow. This could explain the continuous accumulation of PCs throughout longer periods of As exposure.

Production of phytochelatins (PCs) in response to cadmium uptake in the benthic macroalgae Vaucheria compacta and V. debaryana (Xanthophyceae) was investigated. The algae synthesized thiol-containing peptides, identified by means of high-performance liquid chromatography as PC2, PC3 and PC4. In both algal species the level of PCs increased with time of cadmium exposure and was dependent on external cadmium concentration. V. compacta synthesized significantly more PCs than V. debaryana. Exposure of the algae to cadmium at low temperature and in darkness resulted in a significant decrease in PC content over the time interval tested (3 days).