PHYTOTOXICITY OF ALUMINUM-FLUORIDE COMPLEXES AND THEIR UPTAKE FROM SOLUTION CULTURE BY AVENA-SATIVA AND LYCOPERSICON-ESCULENTUM

Avena sativa (oats) and Lycopersicon esculentum (tomatoes) were grown in dilute nutrient solutions supplemented with Al only, F only or a co mbination of both. In solutions containing Al and F, shoot growth was limited when predicted Al-r (Al3+, AlOH2+ and Al(OH)(2)(+)) activities were < 0.1 mu M, activities three orders of magnitude lower than the critical value determined with Al only. The data suggest that at the a ctivities used in these experiments, Al-r is most toxic, AlF2+ and AlF 2+ are toxic to a lesser extent, and AlF3, AlF4- and F- are least toxi c. Fluoride concentrations in shoots grown in solutions correlated bes t with positively charged AlFx3-x species (i.e. AlF2+ AlF2+) and the m olar ratio of F:AI in most plants shoots was about 3:2. However, when activities of positively charged AIF(x)(3-x) species were low (< 50 mu M) and the activity of AlF3 species high (500 mu M the molar ratio of F:Al in plant shoots suggested AlF3 was taken up. These findings are discussed in relation to plant uptake and toxicity. Measured concentra tions of Al-r and F- in solutions containing Al and F were compared wi th concentrations predicted by a computer model (GEOCHEM-PC). The meth od for measuring F- concentrations, using a noncomplexing buffer and F ion-selective electrode, gave good agreement with predicted F-concent rations. The 8-hydroxyquinoline method for measuring Al-r concentratio ns did not agree with predicted concentrations, highlighting the limit ations of this method when measuring Al-r in the presence of F in a mu lti-ligand system with high concentrations of F and Al.