ISSN 1021-4437, Russian Journal of Plant Physiology, 2009, Vol. 56, No. 4, pp. 480–487. © Pleiades Publishing, Ltd., 2009.
Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 4, pp. 530–538.
Excretion of the substances by the roots is an impor-
tant vital function of the plant organism involved in the
formation of plant associations and functioning of bio-
cenoses  because it may participate in the defense of
plants against competitors and pests, ensure protection
from toxic agents , suppress propagation of some
microorganisms, and stimulate reproduction of others
. A wide range of effects exerted by root exometab-
olites is accounted for by a diverse chemical nature of
the substances excreted to the medium .
It was shown that the “root–microenvironment” sys-
tem is formed in the earliest stages of growth. Quanti-
tative and qualitative composition of root microenvi-
ronment may control root cell metabolism. Investiga-
tion of the operation of the “root–microenvironment”
system is necessary not only for the comprehension of
the mechanisms of root growth but also for the use of
this phenomenon in “rhizosphere technologies,” for
instance, for the production of biologically active sub-
stances, rhizoﬁltration, etc. .
In 1990, when the so-called border cells were
described , active investigation of these cells started.
Border cells (BCs) come off (are scaled off) from
the root surface and get over to the rhizosphere .
Separation of BCs from the root is a result of solubili-
zation of the cell wall by pectin methylesterase [5, 6].
BCs produce a gel sheath around the root apex as a
result of excreting pectin polysaccharides, arabinoga-
lactan proteins , and glycine-rich proteins .
One can assume that the rate of BC release and
excretion of substances by them may depend on various
factors, such as toxic agents, the rate of root growth,
and the formation of microenvironment. However, the
effect of biotic and abiotic factors on BCs is still poorly
Earlier, we have estimated the number of BCs in the
root apex of 1-day-old wheat seedlings detected in vitro
. One can assume that BCs are a heterogeneous
population of the cells differing in spatial location in
the gel sheath and in the contribution to total excretory
activity of the root.
The number of BCs in the early stages of root
growth in 1-day-old wheat seedlings was determined in
two ways: (1) by microscopic examination of cytologi-
cal preparations of the roots in situ and (2) after prepar-
ative collection of BCs. Subsequently, by the number of
BCs and viscosity of the gel sheath, we estimated the
effect of a phytotoxic compound (sodium ﬂuoride) on
excretory activity of the root.
MATERIALS AND METHODS
The experiments were conducted with winter wheat
L.), cv. Donetskaya-48. By
50 grains that began germination were placed in the
petri dishes 9 cm in diameter and by 5 ml of distilled
water was added therein. In the experiments with NaF,
by 5 ml of 1, 5, 10, or 20 mM solution of chemically
pure NaF was added to the dishes with the grains. The
Effect of Sodium Fluoride on the Root Apex Border Cells
in One-Day-Old Wheat Seedlings
A. I. Bozhkov, Yu. A. Kuznetsova, and N. G. Menzyanova
Research Institute of Biology, Khar’kov National University, pl. Svobody 4, Khar’kov, 61077 Ukraine;
Received November 6, 2007
—The number of border (scaled off) cells (BCs) was determined in the root apex of 1-day-old wheat
L.) seedlings. Microscopic examination of cytological root preparations showed that in 24
h the number of BCs in the gel sheath of the root apex was 30–40 per root. When the gel sheath was prepara-
tively removed, their number per root increased twice. It is assumed that the subpopulation of BCs directly asso-
ciated with the root apex differs from the subpopulation of BCs freely accommodated in the gel sheath. The number
of BCs was the same in the roots with low and high natural growth rates. NaF (1–20 mM) suppressed growth of wheat
seedling roots; the viscosity of the gel sheath increased (by 3–5 times), and the number of BC rose with the most
pronounced increment in the size of the BC subpopulation directly associated with the root apex.
Key words: Triticum aestivum - border cells - root cap - NaF
: BCs—border cells; HGR—high growth rate;
LGR—low growth rate.