ISSN 10214437, Russian Journal of Plant Physiology, 2012, Vol. 59, No. 4, pp. 502–514. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © S.S. Medvedev, 2012, published in Fiziologiya Rastenii, 2012, Vol. 59, No. 4, pp. 543–556.
Activities of individual organs, tissues, and cells in
any multicellular organism should be coordinated in
order to enable integrated functioning of the organism
as a whole. One of the most essential elements of plant
integrity is polarity, i.e., the axial spatial organization
of plant body. The term polarity means
tation of plant activity and morphogenesis in space.
Polarity can be also defined as the existence of function
ally significant asymmetric structures that are formed in
response to vectorial cues (external or internal).
polarity implies the presence of a well
developed longitudinal axis bearing lateral organs, i.e.,
lateral branches and roots, leaves, and flowers. The
axially organized growth of cells and tissues precludes
the formation of a shapeless bulk of living matter. All
plant organs and tissues are initiated symmetrically
along the plant axes. In addition to axial polarity, dor
soventral and radial polarities are also distinguished.
Nevertheless, the term polarity denotes in most cases
the axial polarity.
Polarization can be induced by physical factors
(light, gravity, electric and magnetic fields) and by
chemical agents (hormones, ions). Particularly effec
tive means of cell polarization is the creation of local
ion gradients, the gradients of Ca
, and H
particular [1, 2]. A distinctive feature of polarizing
cues is their directional (vectorial) mode.
CELL BASES OF POLARITY
Possible mechanisms of polarization at the plant
cell level were first considered by Bentrup  and
Schnepf . They believed that polarization is basi
cally related to axial gradients of bioelectric potentials
(BEP) arising from changes in membrane ionic per
meability, primarily to Ca
, and H
polar cell growth, e.g., growth of pollen tubes or root
hairs, is characterized by several features such as the
gradient focused in the direction of
growth, polarization of the actin cytoskeleton, and the
apical transport of membrane vesicles with their sub
sequent exocytosis. The formation of symmetry axes
in plant cells involves also monomeric GTPbinding
proteins, phosphoinositides, and Cadependent pro
tein kinases .
Electric Polarization of the Plant Cell
The electrophysiological polarity axis of the
nascent plant is established at the earliest stages of
plant development. Within 30 min after fertilization,
the zygote of a brown alga
polarized. At this stage, the inward electric current was
recorded in the nascent rhizoid area and the outward
current was observed on the opposite cell side where
the incipient thallus emerged. The highest density of
Mechanisms and Physiological Role of Polarity in Plants
S. S. Medvedev
Department of Plant Physiology and Biochemistry, St. Petersburg State University,
Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia;
fax: 7 (812) 3289703; email: email@example.com
Received June 25, 2011
—The concept of polarity was the starting point for the attempts of many investigators to understand
the principles of differentiation, because the polar organization underlies specific threedimensional struc
ture of the organism and provides for the integrity and coordination of its functions. The polarity axes are
established at the stage of zygote, extending to the developing embryo, and they “vectorize” subsequent plant
growth and development. Polarization of cells and tissues is crucial for plant morphogenesis, because the
emerging morphogenetic gradients provide the basis for differential genome activity at various stages of plant
development. This review deals with the polarity phenomena and the mechanisms of symmetry axis forma
tion at the level of cells and plant tissues. The roles of electrical gradients, Ca
ions, auxin, cytoskeleton,
ROPproteins, phosphoinositides, and microRNA in polarization of cells and tissues are considered.
higher plants, growth and morphogenesis, polarity, physiological gradients, polar IAA transport,
bioelectric potential gradients, polar Ca
fluxes, cytoskeleton, ROPGTPases, microRNA.
: BEP—bioelectric potentials; IP
trisphosphate; NPA—naphthylphtalamic acid; TIBA—2,3,5tri