The cyanobacterial symbionts in some Nostoc-containing
lichens
were investigated using the nucleotide sequence
of the highly variable cyanobacterial tRNALeu
(UAA) intron. When comparing different Nostoc-containing
lichens, identical intron sequences were found in different samples
of the same lichen species collected from two
remote areas. This was true for all species where this comparison
was made (Peltigera aphthosa (L.) Willd., P.
canina (L.) Willd. and Nephroma arcticum (L.) Torss.). With
one
exception, a specific intron sequence was never
found in more than one lichen species. However, for two of the
species, Peltigera aphthosa and Nephroma arcticum,
two different cyanobionts were found in different samples. By
examining a P. aphthosa photosymbiodeme it could
be shown that the same Nostoc is present in both bipartite
and tripartite lobes of this lichen. It is thus possible for
one cyanobiont/Nostoc to form the physiologically
different symbioses that are found in bipartite and tripartite
lichens. The connection between photobiont identity and secondary
chemistry is discussed, as a correlation
between differences in secondary chemistry and different
cyanobionts/Nostocs in the species Peltigera
neopolydactyla (Gyeln.) Gyeln. was observed. It is concluded
that more knowledge concerning the photobiont will
give us valuable information on many aspects of lichen biology.