Chelating organic acids hampered the hydrolytic reactions of Al and affected the nature of the crystalline aluminum hydroxides. Chemical composition, structure, size, nature of functional groups, and concentration of each organic anion, as well as the pH of the system, controlled the rate of Al(OH)3 crystallization. The order of effectiveness of the various acids was: glutaric < succinic = phthalic < glycine < malonic < glutamic < aspartic < oxalic < salicylic = malic < citric < tartaric. An increase in the stability of complexes formed between the organic ligands and Al decreased the rate of crystallization and changed the final aluminous products from bayerite to nordstrandite and/or gibbsite and then to pseudoboehmite and/or amorphous material. In the presence of anions with a great affinity for Al, particularly at pH equal to or less than 9.0, the reaction products were commonly poorly crystalline or structurally distorted. In the range of pH 8.0 to 10.0 moderately or strongly chelating anions acted to retard or prevent olation and facilitated the formation of stable pseudoboehmite or X-ray-amorphous products. The stronger the chelating power or the higher the concentration of organic anions, the easier was the formation of pseudoboehmite or amorphous material.

Nordstrandite was obtained synthetically by precipitation of Al(OH)3 at pH 9.0 to 11.0 in citrate or malate systems with Al: carboxylic acid molar ratios of 10–100 in the absence and in the presence of montmorillonite. Examination by transmission and scanning electron microscopy showed that the nordstrandite had a tabular morphology in the clay-free systems with Al: carboxylic acid ratio >50. Because the inhibiting effect on crystallization of the citrate or malat e anion decreases with increase in pH, the crystal size varied from <2 μm at pH 10 to 5 μm at pH 11. With increasing concentration of citrate or malate, the nordstrandite crystals became more elongated in the c-direction probably due to organic anion occupation of the coordination sites of Al on the edge faces parallel to the c-axis. Irregular growth along the c-axis was probably due to steric hindrance by the organic ligands distorting the arrangement of the unit layers of nordstrandite.

The catalytic effect of montmorillonite on the formation of nordstrandite was confirmed. Nordstrandite synthesized in the presence of montmoriUonite at pH 9.0 presented an ill-defined ovoidal outline (0.2–0.5 μm), some showing shafts of bayerite growing from the center. At higher pH, where conditions for crystalline growth were again more favorable, nordstrandite crystals nucleated on the montmorillonite surfaces and condensed in clusters of weak face-to-face associations of plates.

Cellular responses to copper stress were investigated for the first time in a saxicolous lichen species, Lecanora polytropa (Hoffm.) Rabenh. Bright blue-green apothecia accumulated up to 1·3% Cu on a dry weight basis (205 μ mol Cu g−1), c. 50% in an exchangeable form. A bright turquoise-blue layer extended beneath the hymenium into the medulla, above and between a dentate photobiont layer. Oxalic (1·88 μ mol g−1), citric (0·83 μ mol g−1) and lower concentrations of malic (0·45 μ mol g−1) acids were determined by GC/MS analysis. Short-term exposure to high Cu2+ concentrations (40 and 400 μ mol g−1) under non-complexing conditions caused a dose-dependent decrease in chlorophyll a content; chlorophyll b and total carotenoid contents remained constant. The phaeophytinization quotient remained unchanged during Cu2+ exposure. Analysis of thiol peptides confirmed glutathione was reduced (GSH) in native L. polytropa (0·538 μ mol g−1), and phytochelatins (PC2 and PC3) oxidised. Short-term exposure to 40 μ mol g−1 Cu2+ oxidised c. 28% of the glutathione pool; oxidised phytochelatin concentrations remained unchanged. This is the first report of phytochelatin production and thiol peptide status in a crustose lichen. These represent two possible detoxification mechanisms in this Cu-tolerant species. Copper complexation by low molecular mass organic acids and non-protein thiols do not entirely account for its tolerance.