Dissociation and metal-binding characteristics of yellow lichen substances suggest a relationship with site preferences of lichens

Abstract

Metal complexation by lichen substances could be a prerequisite for lichen substance-mediated control of metal uptake. Assuming such an effect at pH values where the affinity of the metal for the lichen substance is intermediate would explain the strong preference of lichens with usnic or rhizocarpic acids to acidic substrata. Moreover, it would explain the preference of lichens with parietin and some lichens with compounds of the pulvinic acid group either for nutrient-rich substrata at low pH or for calcareous substrata.

Lichen Substances Prevent Lichens from Nutrient Deficiency

“…However, although members of the same family (Parmeliaceae), both lichens differ in their morphology, which is also likely to affect element uptake. Complex formation of UA and Cu 2+ in the pH range preferred by UA-producing lichens (pH 3.5-6; Takani et al 2002;Hauck and Jürgens 2008;Hauck et al 2009) suggests that these complexes are involved in the observed promotion of Cu 2+ uptake. Whether such lipophilic complexes directly cross the phospholipid membrane (as proven for uncomplexed UA; Abo-Khatwa et al 1996;Hauck and Jürgens 2008) or Cu 2+ ions are transferred to transporters is unclear.…”

“…Given the multitude of compounds and their widespread ability to interact with metal ions (Hauck and Huneck 2007), it is likely that promotion of nutrient uptake will be seen in other lichen symbioses. Recent UV-spectroscopic studies in yellow and orange lichen substances, including UA, suggested that promotion of metal uptake by lichen substances might be widespread (Hauck et al 2009). Lichen compounds that occur in lichens of nutrient-poor sites form complexes with metal ions precisely at the pH ranges preferred by the respective lichens.…”

“…Lichen compounds that occur in lichens of nutrient-poor sites form complexes with metal ions precisely at the pH ranges preferred by the respective lichens. Lichens growing under pH conditions, at which lichen substances do not bind to metals, are limited to substrata rich in mineral nutrients (Hauck et al 2009). Research is necessary to elucidate the extent to which lichen substances are involved in the metal homeostasis of lichens.…”

Lichen deterioration of asbestos and asbestiform minerals of serpentinite rocks in Western Alps

“…On the other hand, the detected mineral deterioration may be related to the release of secondary metabolites such as pulvinic acid, the precursor of the crystalline deposits observed in the cortex layer and characterizing the Candelariella genus ( Culberson, 1979). Pulvinic acid, as oxalic acid, displays acidic and chelating functions that make it active in complexing metals, including Mg 2+ , Fe 2+ and Fe 3+ , in the alkaline range ( Hauck et al, 2009) which often characterizes water and soils deriving from serpentinized ultramafic rocks ( Alexander et al, 2007), including asbestos rich serpentinite sediments ( Schereier et al, 1987). Accordingly, the fibres produced upon incubation for 35 days with oxalic acid not only are similarly modified in their chemical composition to those colonized by C. vitellina, but are likely modified through a similar dissolution pathway, thus being suitable for testing the potency to release ROS of lichen deteriorated fibres.…”

Iron and phosphate uptake explains the calcifuge–calcicole behavior of the terricolous lichens Cladonia furcata subsp. furcata and C. rangiformis

“…A typical character of lichens is their ability to store large amounts of cations in the apoplast that can be taken up intracellularly with delay (Hauck et al 2006). Cation-binding sites in the cell wall and lichen secondary metabolites (Hauck et al 2009) are apparently involved in this process.…”