Biology Reference
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to the cell walls of the cyanobiont
Nostoc
sp. (Lockhart
et al
., 1978). Likewise, Ingram (1982) conducted
a detailed survey of haemagglutinins and haemolysins from the extracts of 36 species of lichens
from 19 genera. The assays involved 20 types of erythrocytes and the extracts of
Usnea fragilescens
,
Parmelia caperata
and
Lepraria incana
exhibited haemagglutinin and haemolysin activities to over
13 and 10 types of erythrocytes, respectively. Proteins extracted from the lichen thalli of
Xanthoria
parietina
could bind to the cell surface of the cultured material of the phycobiont but not to the
freshly isolated phycobionts. Using fl uorescamine-labelled proteins from
X
.
parietina
, Bubrick and
Galun (1980) demonstrated strong binding to the cultured phycobionts obtained from
X
.
parietina
,
Caloplaca
auriantia
and
C
.
citrine
but not to the cultured or freshly isolated phycobionts from the
thalli of
Cladonia convoluta
,
Ramalina duriaei
and
R
.
pollinaria
. The binding very much depended on
the cell wall chemistry of the phycobiont and specially has been correlated with the presence of high
levels of acidic polysaccharides. Further, the binding of fl uorescamine-labelled protein could also
bind to the isolated cell walls of the phycobionts. Lectins from the thalli of
Peltigera horizantalis
have
been found to bind to the cell surface of cultured phycobionts but not to the cell surface of freshly
isolated phycobionts (Petit, 1982). Another purifi ed phytolectin from
Peltigera canina
var
canina
has
been found to be thermostable with a molecular weight of 80,000-90,000 and it could be used as
cytochemical marker in tissue (Petit
et al
., 1983). In order to visualize the cell surface receptors of
mycobionts and phycobionts through fl uorescence microscopy, Marx and Peveling (1983) employed
a number of purifi ed lectins. The mycobionts showed more affi nity to most of the lectins than the
phycobionts. However, all investigated species of
Trebouxia
could bind lectin ConA to their cell
surface but not to the cell surface of the two species of
Pseudotrebouxia
.
Cultures of the mycobiont from the thallus of
Xanthoria
produced ABP that is restricted to the cell
walls of the mycobiont and has a molecular weight of 12 kDa (Bubrick
et al
., 1981, 1985). A similar
ABP from cyanolichen
Nephroma laevigatum
revealed a heterodimeric structure with 52 kDa and 55
kDa subunits (Kardish
et al
., 1991). Characterization of lectins with homodimer structure from the
thalli of
Peltigera membranacea
(Lehr
et al
., 1995) and
P
.
aphthosa
(Lehr
et al
., 2000) has been reported.
Similarly, a homodimeric (each subunit with 16.5 kDa) lectin with haemagglutinating activity has
been purifi ed from the lichen
Dictyonema glabratum
which harbours
Scytonema
as a photobiont.
Structurally, it has been shown to be a glycoprotein with neutral monosaccharides galactose, xylose,
glucose, mannose, in addition to glucosamine. The haemagglutinating activity of the lectin has
been inhibited by N-acetylgalactosamine (Elifi o
et al
., 2000). A glycoprotein lectin with D-galactose
specifi city has been reported from the tripartite lichen
P
.
aphthosa
(Feoktistov
et
al
., 2009).
The ABPs from
X
.
parietina
,
Evernia prunastri
and
P
.
canina
have been characterized. The ABP from
X
.
parietina
has been shown to be a lectin exhibiting arginase activity that can hydrolyze arginine
to ornithine and urea (Molina
et al
., 1993). While ABP is retained by the mycobiont,
X
.
parietina
also
secreted a lectin that too possessed the arginase activity. This is designated as sectered arginase
of
Xanthoria
(SAX). Both of them differed in the glycosyl moieties.The glycosyl moiety of SAX is
composed of galactose and glucose while the endogenous arginase contained equimolar amounts of
N-acetyl-D-glucosamine and glucose (Molina and Vicente, 1995, 1996, 2000). The SAX and the ABP
have the same molecular mass and the same qualitative amino acid composition. That is why these
two glycoproteins have been considered as isolectins (Molina and Vicente, 2000). When purifi ed ABP
from
X.
parietina
was administered to the cultures of phycobiont of the same thallus, in the absence
of the cell wall receptor for the ABP, cellular disorganization took place (Molina and Vicente, 1996).
This has been attributed to an increase in the concentration of algal putrescine followed by apparent
loss of chlorophyll. The loss of chlorophyll has been suggested to be due to putrescine-activated
glucanse activity that led to the disruption of the membranes (Molina
et
al
., 1998a). Ferritin- or
