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Determinant factors for the formation of the calcium oxalate minerals, weddellite and whewellite, on the surface of foliose lichens

Published online by Cambridge University Press:  28 March 2007

Paolo Giordani
Affiliation:
Dipartimento per lo Studio del Territorio e delle sue Risorse (Dip.Te.Ris), Botanica, Università di Genova, corso Dogali 1/M, 1-16136 Genova, Italy.
Paolo Modenesi
Affiliation:
Dipartimento per lo Studio del Territorio e delle sue Risorse (Dip.Te.Ris), Botanica, Università di Genova, corso Dogali 1/M, 1-16136 Genova, Italy.
Mauro Tretiach
Affiliation:
Dipartimento di Biologia, Università di Trieste, Via Giorgeri 10, 34127 Trieste, Italy.

Abstract

The factors influencing the predominance of one of the two mineral forms of calcium oxalate (CO), the monohydrated whewellite (COM) and the di-hydrated weddellite (COD), forming the pruina of the upper cortex of lichens, have been investigated through a simple, sensitive histochemical assay: toluidine blue O (TBO), a metachromatic staining test. The differential reactivity of 43 thalli of 17 pruinose foliose species, supplemented by X-ray diffraction analysis and observations with polarizing and scanning electron microscopy, suggests that the histochemical reactivity of hyphal walls and cementing substances of the upper cortex are related to the density of anionic charges. These factors are probably due to the occurrence of polyuronic acid substances that strongly affects the mineralization of CO. Di-hydrated wedellite is always associated with TBO metachromatic reactivity, and COM with orthochromatic reactivity. When the material has an ambiguous ortho/metachromatic reactivity, COD and COM may occur together. This study presents the first experimental evidence that in lichens CO biomineralization is at least partially biologically controlled.

Type
Research Article
Copyright
Copyright © British Lichen Society 2003

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