EFFECT OF THE NITROGEN STATUS ON COPPER ACCUMULATION AND POOLS OF METAL-BINDING PEPTIDES IN THE PLANKTONIC DIATOM THALASSIOSIRA-PSEUDONANA

Effects of the algal cellular nitrogen status on the defence against c opper toxicity were studied in batch cultures of the coastal diatom Th alassiosira pseudonana, grown in coastal seawater (Oosterschelde, SW N etherlands; 30 parts per thousand salinity). The media represented nut rient-poor (summer) and nutrient-rich (winter) conditions, both withou t and with additional nitrate, respectively. In the summer series, ini tial inorganic N:P ratios were 1.5 and 7.1. In the winter series, N:P ratios were 12.2 and 18.4. Cu was added at five levels (0-315 nM). We expected a low cellular nitrogen status to limit the synthesis of meta l-binding peptides (phytochelatins). In N-enriched summer media phytoc helatins were detectable (HPLC) only at the upper Cu level. In N-enric hed winter media phytochelatins were detectable (14.6 mu M SH) even wi thout additional Cu (pCu similar to 14; pZn similar to 8), whilst in l ow-nitrate winter media, phytochelatins were induced at somewhat highe r Cu additions; cellular Cu concentrations were similar in both cases (similar to 25 mu M). In general, cells accumulated more Cu, Mn and Zn (summer and winter series) in N-enriched media, compared to low-nitra te media. In the low N:P media (summer) division rates were hardly aff ected by Cu. At N:P 12.2 and N:P 18.4, at cellular metal levels identi cal to those in low N:P media. T. pseudonana proved to be more Cu sens itive. In these nitrogen-rich winter conditions, phosphorus deficiency could have played a role. It was discussed that a P limitation might result in an impaired exclusion/export of copper. Phytochelatins appea red in T. pseudonana at cellular atomic C:N ratios lower than similar to 15, and at ambient inorganic N:P ratios higher than the Redfield ra tio (similar to 16). Phytochelatins indicate metal toxicity (sensitivi ty) rather than available metal concentrations in the coastal marine e nvironment, and will not be detectable at natural background concentra tions of Cu and Zn under a nitrogen limitation. (C) 1998 Elsevier Scie nce B.V. All rights reserved.