ISSN 1021-4437, Russian Journal of Plant Physiology, 2008, Vol. 55, No. 6, pp. 843–845. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © I.M. Andreev, 2008, published in Fiziologiya Rastenii, 2008, Vol. 55, No. 6, pp. 931–933.
Over the last few years G.A. Velikanov and coau-
thors from Kazan Institute of Biochemistry and Bio-
physics (Kazan Research Center, Russian Academy of
Sciences, Kazan) have published a series of papers in
the Russian Journal of Plant Physiology [1–4] ﬁnding
evidence for the existence in plants of the vacuolar con-
tinuum or, simply speaking, the vacuolar symplast. The
authors’ contention is that vacuoles of adjoining cells
are interconnected, forming a uniﬁed compartment by
means of specialized structures supposedly integrated
into the plasmodesmata. Data underlying the vacuolar
symplast concept were obtained with a pulsed magnetic
ﬁeld gradient NMR. This method provides a means to
study restricted self-diffusion of water molecules in
various cell compartments and plant tissues and to eval-
uate the effective coefﬁcient of water self-diffusion.
The hypothesis on the existence of the vacuolar
symplast stems from the notion of continuous endo-
plasmic network in plant tissues [5–7]. The ideas, put
forward in the works [5–7], are based on microscopic
observations of various plant tissues. Speciﬁcally, the
possibility that vacuoles of adjoining cells are intercon-
nected through the plasmodesmata is considered [6, 7].
However, the idea of the vacuolar symplast is quite
speculative and has not been proven by convincing
experimental evidence. This idea was not even cited by
other researchers dealing with plasmodesma function-
ing ( and references therein). Although publications [1–7]
raised new discussion in the literature, they are seri-
ously ﬂawed, which casts doubt on the validity of con-
clusions drawn by Velikanov et al. [1–4].
First, the purpose of investigations undertaken by
Velikanov et al. [1–4] is poorly stated from a theoretical
viewpoint, because the challenging physiology prob-
lem remains unclear. Therefore, the authors appeal to
the hypothesis proposed in [5–7] as the only argument
in formulating the nature of the problem, even though
this hypothesis remains largely unproven.
Second, the authors completely neglect alternative
interpretations for changes in relaxation characteristics
of spin echo signals under the action of some metabolic
inhibitors (e.g., sodium azide) and consider these
changes as related exclusively to alterations in water
permeability of plasmodesmata, even though other fac-
tors may play a crucial role. The interpretation sug-
gested by Velikanov et al. is largely based on the sensi-
tivity of spin echo relaxation to some agents that were
reported capable of modulating the plasmodesma con-
ductance. In other words, the inference of plasmodes-
mata as a determinant factor for the restricted self-dif-
fusion of water molecules in maize root tissues is
entirely based on the inhibitor analysis. However, a
closer inspection of the data presented in [1–4] and
publications cited therein shows that the authors’ inter-
pretation is quite subjective. For example, the meaning
of the cited work , principally signiﬁcant for the
interpretation, is conveyed in a distorted manner. Veli-
kanov et al. declare that sodium azide closes plas-
modesmata due to the 80% decrease in intracellular
ATP content and support this statement by referring to
studies with wheat roots . However, Cleland et al. 
and other researchers  actually observed the plas-
modesmata opening in the presence of sodium azide, in
evident contradiction with the statement of Velikanov et al.
Furthermore, the question remains open as to which
extent the ATP concentration decreases in maize root
cells in the presence of this inhibitor, because the
authors did not measure the ATP content. In addition,
the experimental conditions applied by Velikanov et al.
substantially differed from those used by Cleland et al.
. Thus, the initial functional state of most plas-
modesmata in maize root tissues sampled for NMR
studies remains unknown, because the above consider-
ations imply that ATP is needed for plasmodesmata
closing rather than their opening [8–10].
Third, the results of experiments with antibodies to
-pyrophosphatase are not entirely con-
vincing, despite the authors contention that these exper-
iments prove the localization of the tonoplast within the
plasmodesmal pore or in immediate vicinity to plas-
The Vacuolar Symplast: Does It Really Exist in Plants?
(Comments on Publications of G.A. Velikanov et al. in Russian
Journal of Plant Physiology)
I. M. Andreev
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 December 27, 2007