ISSN 1021-4437, Russian Journal of Plant Physiology, 2008, Vol. 55, No. 4, pp. 475–479. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © E.A. Pavlova, A.I. Maslov, 2008, published in Fiziologiya Rastenii, 2008, Vol. 55, No. 4, pp. 529–534.
Lichens are symbiotic associations of heterotrophic
fungi (mycobiont) and autotrophic algae (photobiont).
Usually the photosynthesizing components of lichens
are green unicellular algae, in some cases cyanobacte-
ria, or both.
The symbiosis is based on the integration of the
biont metabolic systems controlling mutual exchange
of the basic nutrients, such as carbon and nitrogen .
Mycobiont provision with algal photosynthetic prod-
ucts is intensively studied [2, 3]. It is well known that
up to 90% of assimilated carbon is utilized by the
Nitrogen metabolic integration is less studied and is
mostly related to lichens containing cyanobacteria as
the associated photobiont [4, 5]. The strategy of nitro-
gen metabolism of this group of lichens is determined
by the capacity of cyanobacteria to ﬁx atmospheric
nitrogen, which then is redistributed between bionts.
The lichen associations containing green algae depend
on external sources of organic and inorganic nitrogen.
They are limited in nitrogen nutrition [5, 6] and, as a
rule, have the lower nitrogen content  and respond
stronger to exogenous nitrogen addition as compared to
cyanobacterial lichens [7, 8].
Currently, the interest for nitrogen nutrition of
lichens with green algae intensiﬁes. The uptake, accu-
mulation, and redistribution of different nitrogen forms
were studied in various lichen species [9, 10] differing
morphologically and ecologically [11, 12]. These stud-
ies dealt with integrated metabolism indices because
they were performed on intact thalli of lichens. In this
connection, it is of importance to study nitrogen metab-
olism of lichen bionts as individual organisms.
In this study, the rates of nitrate uptake by bionts iso-
lated from the lichen
sp. were measured. We also
examined the inﬂuence of illumination on nitrate
uptake because it is well known that nitrate reduction in
freely living single-cell green algae is functionally
related to photosynthesis providing energy and carbon
skeletons for this process [13, 14]. The exchange of
assimilated nitrogen between bionts was evaluated
N stable isotope. The main aim was to dem-
onstrate the existence of nitrogen metabolic integration
in lichens with green algae as an associated photobiont.
MATERIALS AND METHODS
Fresh thalli of the lichen
collected in spring in Pushchino (Moscow oblast) were
used. 10 g of the fresh thalli was homogenized in a
blender by two 10-s cycles at 14 000 rpm with 100 ml
of 10 mM phosphate buffer, pH 7.2. Large thallus frag-
ments were separated by ﬁltration through the nylon
cloth, and the smaller ones were fractionated as was
described earlier , and two fractions enriched in
photobiont and mycobiont were obtained.
Puriﬁed photobiont was obtained from the fraction
enriched in photobiont by further homogenization,
repeated ﬁltration through Miracloth (Calbiochem,
Nitrate Uptake by Isolated Bionts of the Lichen
E. A. Pavlova and A. I. Maslov
Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow oblast, 142290 Russia;
Fax: 7(496) 733-0532; e-mail: firstname.lastname@example.org
Received June 21, 2007
—It was found that bionts isolated from the lichen
had a marked difference
with respect to nitrate assimilation. Isolated and puriﬁed photobiont, the green alga
sp. showed no
ability of nitrate absorption. Mycobiont and thallus fragments containing both bionts absorbed nitrate. Illumi-
nation had no essential inﬂuence on the rate of nitrate uptake. The respiratory inhibitor sodium azide decreased
the rate of nitrate uptake by 80–100%, whereas the photosynthetic inhibitor dichlorophenyldimethylurea did
not reduce it. Using mass-spectroscopic technique, it was shown that, in the intact thallus, nitrate was ﬁrst
absorbed by the mycobiont, and only later appeared in the photobiont. Probably such nutritional difference
between bionts serves as one of the mechanisms by which the host fungi control the associated green algae and
support their symbiosis.
Key words: Parmelia sulcata - Trebouxia sp - lichen - thallus - photobiont - mycobiont - nitrate - nitrate uptake
: Chl—chlorophyll; DCMU—dichlorophenyldime-