Abstract
ABSTRACTCadmium inhibits iron uptake and assimilation in the coastal diatom Thalassiosira weissflogii Grun. The effect of cadmium on short term Fe uptake fits ft competitive binding model: image where (Fe3+) and (Cd2++) tire the free ferric and cadmium ion concentrations, respectively. The apparent binding constant Kcds, is calculated to be ca. lO8.2M‐1 compared to a Kfe of lO19 M‐1. At low free ferric ion concentrations. interference of cadmium with iron transport (at pCd = 8 and pFe* < 20) results in a simultaneous decrease in growth rate and Fe accumulation to a level known 1o limit growth. Upon decreasing the free cadmium ion concentration, cells accumulate a large amount oj iron prior to resumption of normal growth. At higher free ferric ion concentrations (pFe* < 20) normal or elevated Fe quotas are absented but “luxury consumption” of iron still occurs upon reversal of toxicity. Evidence that these algae with high cellular iron quotas are effectively Fe deficient is provided by a decrease in the cytochrome f/chlorophyll a ratio and a much greater decrease in NO3‐ reductase activity than in aldolase activity or H14C03 assimilation. Under the conditions of this study, cadmium had little effect on Si accumulation. The transport of methylamine (an analog of NH+4) is unaffected by short term exposure to high free cadmium ion concentration but is greatly inhibited upon long term (97 h) exposure.
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