Message - 7th IAL Symposium

Lichen: from genome to ecosystem in a changing world
4B-P
(4B-P5) Submission ID: IAL0173-00001
LICHENIZED FUNGI PROVIDE AN IDEAL OSMOTIC SPACE BY ADJUSTING THEIR
OWN CELLULAR OSMOLARITY DIFFERENTLY FOR CHLOROBIONTS OR CYANOBIONTS
Kosugi M. 1 , Shizuma R. 2 , Takeuchi A. 3 , Suzuki Y. 3 , Uesugi K. 3 , Koike H. 4 , Fukunaga Y. 2 ,
Miyazawa A. 2 , Kashino Y. 2 , Satoh K. 2
1 Biosphere Research Group, National Institute of Polar Research, Tokyo, Japan
2 Department of Life Science, University of Hyogo, Hyogo, Japan
3 Research & Utilization Division, SPring-8, Japan Synchrotron Radiation Research Institute (JASRI), Hyogo, Japan
4 Department of Biological Sciences, Chuo University, Tokyo, Japan
Lichens are organisms resulted from symbioses between a fungus and either a green alga or a
cyanobacterium. They are known to exhibit extreme tolerance of desiccation. Their all metabolic activities are
stopped in drought condition and rapidly recovered in re-hydration. We investigated the responses of photosystem
against dehydration using chlorolichens (Ramalina yasudae and Parmotrema tinctorum), cyanolichens
(Collema subflaccidum and Peltigera degenii), a cephalodium-possessing lichen (Stereocaulon sorediiferum)
that has a green-algal part and a cyanobacterial part within the same thallus, a green-algal photobiont (Trebouxia
sp.), an aerial green alga (Trentepolia aurea), and a terrestrial cyanobacterium (Nostoc commune). The response
of photosystem to dehydration shown by cyanolichen was almost the same as that shown by a terrestrial
cyanobacterium. The cyanolichen was more sensitive to dehydration than the chlorolichen or the chlorobiont. We
found that the differences in response to dehydration were closely related to cellular osmolarity; osmolarity was
comparable between cyanolichen and cyanobacterium and between chlorolichen and green alga. Furthermore,
in the cephalodium-possessing lichen, the osmolarity of cepharodia and effect of dehydration on cephalodia
were similar to those of cyanolichen. Responses of its green-algal part within the identical thallus were similar
to those of chlorolichens. This indicates that photobionts retain their original properties as free-living organisms,
such as their ability to combat water loss, even after lichenization. More importantly, symbiont fungi adjust their
osmotic pressures for the sake of their green-algal or cyanobacterial partners; providing suitable osmotic environments
to combat desiccation. We conclude that the lichen symbiosis involves a mutual partnership rather
than a commensalism. Inspired by these results, we conducted three-dimensional image analysis by X-ray
microtomography, and we will also discuss on the morphology related to photosynthetic environments of greenalgal
and cephalodia parts of a S. sorediiferum.
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