Surface hydrophobicity causes SO2 tolerance in lichens.
OBJECTIVE
The superhydrophobicity of the thallus surface in one of the most SO(2)-tolerant lichen species, Lecanora conizaeoides, suggests that surface hydrophobicity could be a general feature of lichen symbioses controlling their tolerance to SO(2). The study described here tests this hypothesis.


METHODS
Water droplets of the size of a raindrop were placed on the surface of air-dry thalli in 50 lichen species of known SO(2) tolerance and contact angles were measured to quantify hydrophobicity.


RESULTS
The wettability of lichen thalli ranges from strongly hydrophobic to strongly hydrophilic. SO(2) tolerance of the studied lichen species increased with increasing hydrophobicity of the thallus surface. Extraction of extracellular lichen secondary metabolites with acetone reduced, but did not abolish the hydrophobicity of lichen thalli.


CONCLUSIONS
Surface hydrophobicity is the main factor controlling SO(2) tolerance in lichens. It presumably originally evolved as an adaptation to wet habitats preventing the depression of net photosynthesis due to supersaturation of the thallus with water. Hydrophilicity of lichen thalli is an adaptation to dry or humid, but not directly rain-exposed habitats. The crucial role of surface hydrophobicity in SO(2) also explains why many markedly SO(2)-tolerant species are additionally tolerant to other (chemically unrelated) toxic substances including heavy metals.
Hauck
Markus
M
Albrecht von Haller Institute of Plant Sciences, Dept. Plant Ecology, University of Göttingen, Untere Karspüle 2, D-37073 Göttingen, Germany. mhauck@gwdg.de
Jürgens
Sascha-René
SR
Brinkmann
Martin
M
Herminghaus
Stephan
S
D057927:Hydrophobic and Hydrophilic Interactions; D008011:Lichens / Q000502:physiology*; D013458:Sulfur Dioxide; D014867:Water / Q000502:physiology*; D017155:Wettability
D014867:Water; D013458:Sulfur Dioxide