This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Lichens colonize trees and rocks all over the world. They are symbiotic communities between fungi and photosynthetically active green algae or cyanobacteria, in which both partners benefit from each other: The fungal partner relies on the algae for a supply of carbohydrates and, in return, it protects the algae from UV radiation and other environmental influences.
The contact zone where the fungal cells and algal cells touch is crucial for transferring nutrients between the two symbiotic partners. Detailed investigations, particularly a three-dimensional understanding of this area between the cells, have been lacking until now. A research team led by botanist PD Dr.
Andreas Beck of the Bavarian State Collections of Natural History (SNSB), in collaboration with Prof. Christian Bayer of Aalen University of Applied Sciences, has now succeeded for the first time in visualizing this interaction zone between the two symbiotic partners of the wall lichen Xanthoria parietina in three dimensions. The work is published in the journal Scientific Reports.
The high-resolution nano-CT images show in detail where and how the fungus and algae come into contact via their cell walls—areas inside the lichen that are only a few ten-thousandths of a millimeter in size. For comparison, an average human hair is about 200 times thicker than these structures. It becomes apparent that the algae are directly connected to the filamentous fungal cells via about one-quarter of their cell wall surface area.
The contact area is further increased by a volume expansion of fungal cells located in the immediate vicinity of the algal cells. Specialized material analyses, known as energy-dispersive X-ray spectroscopy, also show that the chemical composition of the cell walls at the fungus-alga contact zones has changed. Both the nitrogen and sulfur content are significantly elevated there, which the researchers suspect may reflect an influence on transport processes between the symbionts.
"Our analyses show, for the first time, the precise modification of the symbiont cell wall in the contact area between the alga and the fungus. Genomic analyses have not provided us with these details so far. The 3D models of the interaction zone between the two lichen symbionts are of great interest for understanding their interaction.
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