PH-ALTERED INTERACTION OF ALUMINUM AND FLUORIDE ON NUTRIENT-UPTAKE, PHOTOSYNTHESIS AND OTHER VARIABLES OF CHLORELLA-VULGARIS

This study presents information on the pH-induced toxicity of AlCl3, A lF3, NaF and AlCl3 + NaF on growth, nutrient uptake, photosynthesis, p hotosynthetic electron transport, enzymes of nitrogen and phosphorus m etabolism and ATPase activity of Chlorella vulgaris. Both PS I and PS II were severely inhibited by the combination of AlCl3 + NaF followed by AlF3, AlCl3 and NaF. Inhibition of acid phosphatase activity was mo re pronounced than alkaline phosphatase. In general, toxicity of all t he test chemicals increased with a downshift in pH. The interaction of AlCl3 and NaF produced additive effect at pH 6.8, and synergistic at pH 6.0 and 4.5. The combination of AlCl3 + NaF did not produce signifi cant difference in the activity of Mg2+ and Ca2+-ATPase in the medium supplemented with 60 and 100 mu M PO43- at pH 6.8. Compared to 60 mu M PO43-, the test organism grown in 100 mu M PO43- containing medium de picted significant increase in Mg2+ and Ca2+-ATPase activity at pH 6.0 and 4.5. Infra-red spectra revealed the formation of AlF4- at pH 6.0 and 4.5 in AlCl3 + NaF supplemented medium as well as in the algal cel ls. Aluminium uptake from the medium containing AlCl3 decreased in the presence of PO43-. This study suggests that phosphate restricts the e ntry of Al into the cell, while fluoride promotes it. AIF, toxicity co uld be due to its interference with phosphate binding site of ATPase t hereby arresting the release of energy. (C) 1998 Elsevier Science B.V. All rights reserved.