ISSN 1021-4437, Russian Journal of Plant Physiology, 2007, Vol. 54, No. 6, pp. 790–796. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © V.N. Zholkevich, M.S. Popova, N.V. Zhukovskaya, 2007, published in Fiziologiya Rastenii, 2007, Vol. 54, No. 6, pp. 885–891.
Recently, we have described the stimulatory effects
of neurotransmitters on root water-pumping activity
. Similar neurotransmitter action was also noted in
earlier publications [2–8]. It manifests in the enhanced
exudation of detached roots and is related to the
increased root pressure due to its metabolic component,
the increased temperature coefﬁcient of exudation
), a reduced exudate osmotic pressure, and
decreased root hydraulic conductivity. It turned out that
a stimulatory effects of all neurotransmitters tested
(acetylcholine, adrenalin, noradrenalin, and serotonin)
was completely abolished in the presence of microﬁla-
ment- and microtubule-disrupting drugs and also
uncouplers of oxidative phosphorylation. The effects of
aforementioned agents were not limited by only neu-
tralizing of neurotransmitter stimulatory action. Exuda-
tion was suppressed to the same degree as in the pres-
ence of only cytoskeleton drugs or oxidative phospho-
rylation uncouplers in the absence of neurotransmitters
[4, 5, 7]. This fact is especially important. It could indi-
cate that, during exudation stimulation, the targets of
neurotransmitters are energy-dependent contractile
systems. This supposition is conﬁrmed by the absence
of any additivity of various neurotransmitter stimulat-
ing effects at their combined application in each com-
binations . The reason for such additivity absence
could be a commonness of neurotransmitter targets,
and the cytoskeleton is evidently such a target.
Stimulatory Effects of Adrenalin and Noradrenalin on Root
Water-Pumping Activity and the Involvement of G-Proteins
V. N. Zholkevich, M. S. Popova, and N. V. Zhukovskaya
Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, 127276 Russia;
fax: 7 (495) 977-8018; e-mail: Zhvn@ippras.ru
Received April 12, 2007
—To evaluate the involvement of G-proteins in the signal transduction during stimulatory action of
neurotransmitters, adrenalin and noradrenalin, on root exudation and the ivolvement of G-proteins in water
transport in the root and creaction of the root pressure, we tested the effects of guanosinethiodiphosphate, an
inhibitor of GTP-binding capacity of G-proteins, and guanosinethiotriphosphate, a stimulator of this capacity.
Experiments were performed with detached roots of 5–7-day-old maize (
L.) seedlings and the mittens
produced from them due to the removal of the vascular cylinder. The latter are a convenient model to study the
nature of the root pressure due to its strongly limited possibility to function as an osmometer during the early
step of exudation. In the “mittens,” adrenalin and noradrenalin enhanced exudation, increased its temperature
), root pressure, and its metabolic component much stronger than in detached roots with the vas-
cular cylinder retained (conventionally named as “intact” roots). In control treatment (with water), guanosineth-
iodiphosphate retarded exudation on the average by 30% in intact roots and by 50% in mittens, simultaneously
from 3.0 to 1.7 in intact roots and from 4.0 to 1.3 in mittens. Guanosinethiotriphosphate exerted
an opposite action: it stimulated exudation on the average by 30% in intact roots and by 60% in mittens; the Q
value increased from 3.0 to 3.6 in intact roots and from 4.0 to 5.8 in mittens. These data indicate that G-proteins
are involved in the control of water transport and creation of the root pressure (without any other treatments).
Guanosinethiodiphosphate neutralized completely adrenalin- and noradrenalin-induced stimulation of exuda-
tion, resulting in the level substantially below the control one, especially in mittens. Guanosinethiotriphosphate
enhanced stimulatory effects of both neurotransmitters, mainly in mittens, whereas its effect on intact roots was
relatively weak, especially in experiments with noradrenalin. It should be emphasized that the mittens
responded to both neurotransmitters and the regulators of G-protein activity much stronger than intact roots.
The data obtained argue for the G-protein involvement in (1) transduction of adrenalin and noradrenalin signals
stimulating root water-pumping activity and (2) the control of water transport and creation of the root pressure
under normal conditions. Experiments with mittens indicate that this G-protein involvement could by mainly
related to the functioning of the root cortex parenchymal cells and the formation of the metabolic component
of the root pressure.
Key words: Zea mays - root - mittens - exudation - signal transduction - G-proteins - neurotransmitters - gua-
nosinethiodiphosphate - guanosinethiotriphosphate
: MC—metabolic component; OP—osmotic pres-
sure; RP—root pressure.