Biology Reference
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1983), habitat preferences (White and James, 1988) and morphology also as in
P
.
aphthosa
group
(Holtan-Hartwig, 1993; Vitikainen, 1994; Goward
et al
., 1995) and
Pseudocyphellaria
(Renner and
Galloway, 1982; Galloway, 1988). The generic identity and the specifi city of the cyanobacterial
strains present in the morphotypes of tripartite lichens have been investigated. Miao
et al
. (1997)
reported the existence of different
Nostoc
strains in the morphotypes of
P
.
membranacea
. On the other
hand, Paulsrud
et al
. (1998) detected that there exists specifi city and the same strain of
Nostoc
is
represented in the morphotypes examined from geographically distant areas in central Sweden and
collection sites in Sweden and Finland. The identity of
Nostoc
strain was based on similarity in the
sequences of intron of tRNA
Leu
(UAA) gene of the photobionts. The bipartite and tripartite lichens
of
P
.
aphthosa
harboured the same
Nostoc
strain as revealed by the matching of intron sequences of
the photosymbiodeme. Similarly, intron sequences of photobiont of one specimen of bipartite lichen
P
.
neopolydactyla
(from central Finland) were similar to the sequences of photobionts of tripartite
lichens collected from Finland and Sweden. It was thus concluded that the apparent diversity in
Nostoc
strains associated with
P
.
neopolydactyla
infact is dependent on the particular fungal chemotype
that establishes the association.
The diversity of photobionts in lichens from geographically distant regions has been studied
by Paulsrud
et al
. (2000). The photobionts of
P
.
membranacea
collected from Oregon (USA) and in
Sweden showed identical sequences of the intron of tRNA
Leu
(UAA) gene. Similarly,
Nephroma
resupinatum
thalli inhabiting Oregon and Finland showed similar sequences of the intron. These
results indicate that the same photobiont is present in particular species of thallus irrespective of its
place of collection. On the contrary, the cyanobionts of
P
.
neopolydactyla
collected from Oregon and
Washington revealed intron sequences different from the sequences of cyanobionts present in the
thalli of
P
.
neopolydactyla
collected from central Finland. At least two different
Nostoc
strains have been
identifi ed in the materials from USA thus confi rming their earlier observations on
P
.
neoploydactyla
(Paulsrud
et al
., 1998). Further, two different
Nostoc
strains were represented in different samples
of
P
.
brittanica
and fi ve different strains seem to be associated with six specimens from Oregon
and Washington based on the intron sequences. The diversity of
Nostoc
strains in populations of
P
.
neopolydactyla
is whether due to the particular chemotype of the fungus involved in the association
or due to the existence of several morphological and chemical races in this species of
Peltigera
remains
to be elucidated. To establish specifi city of the cyanobiont, populations of
P. aphthosa
growing in
fi eld were subjected to asceptic removal of their cephalodia (containing the cyanobiont
Nostoc
) and
seven axenic cultures of
Nostoc
(fi ve isolates from lichen thalli: two strains from
P
.
aphthosa
-
Nostoc
Pa-1 and
Nostoc
Pa-2; one each from
P
.
membranacea
,
P
.
canina
and
N
.
resupinatum
, i.e.
Nostoc
-Pm,
Nostoc
-Pc and
Nostoc
-Nr, respectively;
N
.
punctiforme
PCC 73102 and
Anabaena
sp. strain PCC 7120)
were inoculated on the surface of
P
.
aphthosa
thalli. After the development of new cephalodia, 80 such
cephalodial cyanobionts were analyzed for tRNA
Leu
(UAA) intron sequences and compared with
the sequences of seven axenic cultures as well as those of cyanobionts of thalli occurring in nature.
Interestingly, none of the inoculated strains appeared in the newly generated cephalodia but all the
80 cephalodia contained the same sequences of tRNA
Leu
(UAA) intron that were originally present
in the cephalodia of the thalli at the site. Two of the inoculated strains survived as epiphytes on the
same thalli and they belonged to the isolates from bipartite
Peltigera
species. These results suggest
that cyanobacterial association and lichen-forming fungi can be specifi c and stable (Paulsrud
et
al
., 2001).
Rikkinen
et al
. (2002) subjected cyanobionts of cyanolichens from northern Europe, western north
America and central China for 16S rDNA and tRNA
Leu
(UAA) intron sequence analysis. The former
helped in resolving phylogenetic relationships while the latter enabled in the identifi cation of
Nostoc
