1021-4437/05/5205- © 2005
Russian Journal of Plant Physiology, Vol. 52, No. 5, 2005, pp. 679–684. Translated from Fiziologiya Rastenii, Vol. 52, No. 5, 2005, pp. 763–768.
Original Russian Text Copyright © 2005 by Vysotskaya.
The ratio between root and shoot weights predicted
for successive stages of plant development  is genet-
ically determined . It reﬂects a relationship between
the processes of growth and development of plant
organs and suggests a mechanism that maintains a bal-
ance between shoot and root growth. Thus, after the
excision of a considerable part of roots in various plant
species, the growth of the root system was activated [3, 4];
this process requires a redistribution of assimilates in
favor of roots. It is still unknown how plants control
biomass accumulation by their underground and above-
ground organs. Environmental conditions play a signif-
icant role in the regulation of root and shoot biomass. It
is especially important that plant growth response in the
course of adaptation to stress conditions implies the
coordination of shoot and root growth aimed at the opti-
mization of resource consumption . For instance,
salinization  and deﬁciency in soil nutrients or water
inhibit shoot growth to a greater extent than root growth
, whereas the presence of heavy metals in the root
zone brings about a suppression of root growth .
Regulation of plant organ growth in the terms of
redistribution of resources between various plants parts
has been actively discussed in the literature [9–11].
Young wheat plants with their root system considerably
reduced by excising some roots present a convenient
model for studying the coordination of growth of their
aboveground and underground organs.
Previously  we compared the changes in hor-
monal balance of the intact seedlings and the seedlings
with partially excised roots in order to elucidate the role
of phytohormones in the regulation of the observed
activation of root growth. In this work, we employed a
different experimental design. One of the ﬁve roots was
preserved in order to discern the mechanisms of coor-
dination of shoot and root growth and follow in what
order these mechanisms are switched on when induced
by the loss of some roots.
MATERIALS AND METHODS
Desf., cv. Bezenchukskaya
139) seeds were germinated in darkness on tap water at
. Seedlings were transferred to the containers
ﬁlled with 10% Hoagland and Arnon medium and
placed in the light (14-h photoperiod, 450 mmol/(m
PAR; air temperature of
). The experiments
were conducted with 7–9-day-old seedlings.
A day before the experiments, caryopses were
excised, and seedlings were transferred for adaptation
to the beakers with 100 ml of the nutrient solution.
Immediately before the experiment, the main roots
were examined for the absence of lateral roots. Four out
of ﬁve embryo roots were cut off. Hereinafter, such
plants will be referred to as the experimental plants.
The main root remained after the reduction of the root
system was plunged into the nutrient solution so that
the cuts resulting from the excision of other roots would
be left above the surface of the nutrient solution.
Mechanisms Coordinating Wheat Seedling Growth Response
as Affected by Shoot/Root Ratio
L. B. Vysotskaya
Institute of Biology, Ufa Research Center, Russian Academy of Sciences,
pr. Oktyabrya 69, Ufa, 450054 Russia;
Received September 28, 2004
—Excision of four out of ﬁve roots in 7-day-old wheat seedlings (
Desf.) rapidly sup-
pressed shoot growth promoted biomass accumulation by the remained root largely due to its expanded branch-
ing. Next, the rate of shoot growth increased although was not completely recovered. After the reduction of the
root system, the rate of photosynthesis in the leaves of seedlings did not decrease. As compared to the intact
plants, auxins and cytokinins accumulated in the remained root, whereas in the growing part of the shoot, the
level of auxins rapidly declined. Shoot growth rate was assumed to decrease after the excision of a part of the
root system due to lower extensibility of growing tissue, and the promotion of lateral root formation on the
remained root apparently resulted from active redistribution of phytohormones and assimilates between plant
organs. The prime role of hormonal signals in the coordination of shoot and root growth is discussed.
Key words: Triticum durum - growth - lateral roots - IAA - cytokinins
: IEA—immunoenzyme analysis; PAR—photosyn-
thetically active radiation.