ISSN 1021-4437, Russian Journal of Plant Physiology, 2006, Vol. 53, No. 3, pp. 298–304. © MAIK “Nauka /Interperiodica” (Russia), 2006.
Original Russian Text © E.A. Egorova, N.G. Bukhov, A.G. Shugaev, D.A. Los, 2006, published in Fiziologiya Rastenii, 2006, Vol. 53, No. 3, pp. 336–342.
In phototrophic cells of higher plants and single-
celled microalgae, photosynthesis and respiration are
separated spatially and occur in different organelles,
chloroplasts and mitochondria. These organelles
exchange by their reducing and energetic equivalents
with the help of the number of transporters inserted into
organelle membranes . In addition, such exchange
demands diffusion of transferred molecules within the
cytosol of the plant cell . Thus, metabolic interaction
between photosynthesis and respiration in phototrophic
cells of higher plants and microalgae is a complex and
ambiguous process .
As distinct from higher plants, in cyanobacteria the
components of respiratory and photosynthetic electron
transport chains are located in the same membranes.
Moreover, both chains share the same redox-transport-
ers . This permitted a supposition that the rate of
electron ﬂow from respiratory dehydrogenases to the
total pool of quinone electron carriers could change
substantially the rate of electron ﬂow to PSI, which is
not associated with PSII functioning and exerted by the
so-called alternative routes of electron transport .
The absence of spatial separation between respiratory
and photosynthetic functions makes intact cells of
cyanobacteria an attractive model for the investigation
of interaction between these processes. These investi-
gations are facilitated by an easy availability of cyano-
bacterial cells for exogenous glucose, a major respira-
tory substrate. In addition, it is unknown whether
cyanobacterial cells, with their rather homogenous
membrane system devoid of grana, display multiple
routes of electron transport, which are characteristic of
higher plants and related to the heterogeneity of chloro-
plast membrane system, i.e., the occurrence of stromal
and granal membranes .
The objective of this work was to study the effects
of exogenous glucose on the functioning of alternative
pathways of electron ﬂow to PSI, not associated with
the electron inﬂux from PSII, and the rate of respiration
in the cells of cyanobacterium
, one of the
most studied members of this class of phototrophic
organisms [7, 8].
MATERIALS AND METHODS
sp. 6803 phototrophic culture was
grown as describer earlier [7, 8].
Effect of Exogenous Glucose on Electron Flow to Photosystem I
and Respiration in Cyanobacterial Cells
E. A. Egorova, N. G. Bukhov, A. G. Shugaev, and D. A. Los
Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, 127276 Russia;
fax: 7 (495) 977-8018; e-mail: firstname.lastname@example.org
Received October 3, 2005
—The effects of exogenous glucose on the rates of alternative pathways of photosystem II (PSII)-inde-
pendent electron ﬂow to PSI and of dark respiration in
sp. 6803 cells were studied. The presence
of glucose was shown to accelerate the electron ﬂow to
, the PSI primary electron donor oxidized with
far-red light (FRL), which excites speciﬁcally only PSI. An increase in the glucose concentration was accom-
panied by a further activation of electron ﬂow to PSI, which was supported by the dark donation of reducing
equivalents to the electron transport chain. An increase in the external glucose concentration resulted also in the
disappearance of lag-phase in the kinetics of
reduction, which was observed in the cells incubated with-
out glucose after FRL switching off. A similarity of nonphotochemical processes of electron transfer to PSI in
cyanobacteria and higher plants was supposed, basing on the earlier observed fact of the occurrence of such lag-
phase in higher plants and its dependence on the exhausting of stromal reductants in the light. Acceleration of
dark electron ﬂow to PSI in the presence of glucose, a major respiratory substrate, may indicate the coupling
between nonphotochemical processes in the photosynthetic and respiratory chains of electron transport in
cyanobacterial cells. A close correlation between photosynthesis and respiration in cyanobacterial cells is also
conﬁrmed by a sharp acceleration of respiration with an increase in the glucose concentration in medium.
Key words: Synechocystis - alternative pathways of electron transfer - dark respiration - photosynthesis
: FRL—far-red light; PS—photosystem; WL—white