Biology Reference
In-Depth Information
Nephroma
and
Stereocaulon
are able to accept a broader spectrum of
Nostoc
strains as photobionts.
Specimens collected from different geographical regions showed similar
Nostoc
strains suggesting
that
Nostoc
taxa are very widely distributed. In other words,
Nostoc
strains diversifi ed (as the other
Nostoc
strains that associate with
Blasia
and
Macrozamia
) and are versatile in forming bipartite
(
Pseudocyphellaria
crocata
) or tripartite (
Lobaria pulmonaria
) lichens. Strains of
Nostoc
present in lichens
Stereocaulon
spp. and
N. arcticum
(with external cephalodia) do not appear in the '
Pseudocyphellaria
clade' as also certain of the free-living
Nostoc
spp. They concluded that some of the
Nostoc
taxa are
specialized in leading a symbiotic life with only lichen-forming fungi.
Cyanobiont selectivity of eight epiphytic lichens (
Lobaria pulmonaria
, tripartite lichen with
internal cephalodia;
Nephroma
bellum
,
N
.
laevigatum
,
N
.
parile
,
N
.
resupinatum
,
P. triptophylla
,
P
.
leucophlebia
, tripartite lichen with external cephalodia and
P
.
praetextata
) of an old growth forest
area in Finland was examined by sequencing of three gene loci (partial 16S rDNA, partial
rbcL
and
complete
rbcX
gene of the
rbcLX
gene cluster). The above lichen species growing on same old aspen
(
Populus tremula
) and adjacent trees in the same stand were compared to know whether they share
the same cyanobiont or harbour different strains specifi c to the lichen. The main fi ndings can be
summarized as follows: (i) all the lichen species showed the sequence similarities of the cyanobiont
to be
Nostoc
, (ii) there is no correlation of the geographic origin of the samples, (iii) the sequences of
the cyanobionts in all the epiphytic species are distributed into two major clades, (iv) cyanobionts
of
P
.
leucophlebia
and
P
.
praetextata
group together in clade I with four
P
.
leucophlebia
samples from
lithophytic habitats, (v) clade II consisted of two subgroups, subgroup II
a
having the two cyanobionts
from
N. laevigatum
together with cyanobionts of
Degelia plumbea
,
L
.
scrobiculata
,
N
.
helveticum
,
N
.
tangeriense
and
Pseudocyphellaria crocata
and subgroup IIb consisting of all the cyanobionts of
N
.
bellum
,
N
.
parile
,
N
.
resupinatum
and
P
.
triptophylla
irrespective of their geographical origin together
with three cyanobionts of
L
.
pulmonaria
and (vi) the cyanobionts of
L
.
pulmonaria
revealed sequence
similarities to the clade II signifying that
L
.
pulmonaria
is more versatile and can form symbioses
with a wide range of
Nostoc
strains. This could also lead to different
Nostoc
strains in a single lichen
thallus (Myllys
et al
., 2007). In this context, it is interesting to note that the thalli of
L
.
pulmonaria
do
not always contain cephalodia (Zoller
et al
., 1999).
The clades I and II identifi ed by these workers corresponded to those already described earlier
by Rikkinen
et al
. (2002), Lohtander
et al
. (2003) Rikkinen (2003, 2004) and Oksanen
et al
. (2004).
Moreover, following Rikkinen
et al
. (2002) the clades I and II were designated as “
Peltigera
guild”
and “
Nephroma
guild”, respectively based on the ecology of the lichens. Though “
Peltigera
guild”
includes the terricolous lichens, the “
Nephroma
guild” corresponded only to epiphytic lichens of old
growth forests. However, “
Nephroma
guild” does not constitute a homogeneous group of epiphytic
lichens since it consisted of certain other cyanobionts collected from terrestrial and lithophytic
habitats (Stenroos
et al
., 2006).
The variability in the morphotypes of Peltigerineae is whether due to differences in the
photobionts or genetically distinct mycobionts has been investigated. Though the fi rst such
molecular study was conducted by Armaleo and Clerc (1991), the results did not have suffi cient
resolution to distinguish the presence of two species. DePriest and Been (1992) used ITS region of
5.8S gene of lichenized fungus
Cladonia chlorophaea
for such studies. The fungus specifi c primers
designed for mycorrhizal fungi by Egger (1995) were put to test for the amplifi cation of the 5.8S
ITS region of mycobionts using total lichen DNA as template (Goffi net and Bayer, 1997). Further,
these workers also used ITS of 5.8S gene sequences of mycobiont members of photomorph pairs in
P
.
aphthosa
,
P
.
brittannica
,
P
.
leucophlebia
,
N
.
expallidum
and
N
.
arcticum
. One possibility suggested for
the development of a tripartite lichen thallus in the genera studied is the fusion of the chloromorph
