1021-4437/03/5003- $25.00 © 2003
Russian Journal of Plant Physiology, Vol. 50, No. 3, 2003, pp. 305–307. Translated from Fiziologiya Rastenii, Vol. 50, No. 3, 2003, pp. 346–348.
Original Russian Text Copyright © 2003 by Lukatkin, Bashmakov, Kipaikina.
Plant organisms are affected by numerous stress fac-
tors of various origins. Among particularly important
abiotic factors are adverse thermal environments, such
as chilling temperatures in the case of chilling-sensitive
plants [1–3]. Among the anthropogenic factors, the
impact of heavy metals on plants should be mentioned
[4–6]. The toxicity of heavy metals is an important
problem for many industrial regions of Russia and
other countries, because it hampers high-quality agri-
cultural production . A combined action of adverse
climatic and anthropogenic factors substantially dis-
turbs plant functions and decreases crop yields.
The inﬂuence of single stress factors on physiologi-
cal processes in plants has been characterized in detail.
For example, chilling temperatures are known to induce
multiple dysfunctions in chilling-sensitive plants [1–3,
7, 8]. The disturbances are manifested at the cell and
subcellular levels [1, 8] as well as at the whole plant
level [2, 3, 7]. A complex of alterations in physiological
processes upon chilling results in cold-induced injury
of chilling-sensitive plants and a sharp decrease in their
productivity . Ample data has accumulated in the lit-
erature on metabolism, growth, and reproductive func-
tions of cultivated plants exposed to various doses of
heavy metals [4–6].
However, the combined action of stress factors of
different origin remains insufﬁciently characterized.
One may assume that two or several factors applied
simultaneously produce either additive or antagonistic
Possible mechanisms of plant protection under sep-
arate or combined action of stress factors is a matter of
considerable interest. There is some evidence that vari-
ous biologically active substances can alleviate the neg-
ative effects of environmental cues [9–11]. Low-toxic
synthetic phytohormones applied at extremely low con-
centrations [10, 11], e.g., cytokinin analogs [11, 12],
are particularly interesting in this respect. The activity
of some recently synthesized preparations is by several
orders of magnitude higher than that of natural phyto-
hormones. Thidiazuron is one of such substances with
defoliant activity. This synthetic growth regulator
exhibits cytokinin activity at low concentrations and
elevates cold resistance of cucumber leaves .
The goal of this study was to test the inﬂuence of
thidiazuron on cucumber seedlings upon separate and
combined application of cold treatment and heavy met-
MATERIALS AND METHODS
Preparation of plant material.
Seeds of cucumber
cv. Monastyrskii were germinated on distilled water at
C, a 16-h photoperiod, and an illuminance of
5000 lx. On the ﬁfth day, germinated seeds were placed
for 48 h into 0.5 mM solutions of PbNO
O (analytical grade, Russia). The control plants
remained on distilled water. Some plants were treated
with 10 nM thidiazuron (2 ml per plant). Prior to anal-
yses, plants of each treatment were divided in two
groups; some groups were placed in a chilling chamber
C) for 24 h, whereas other groups were kept for 24 h
at room temperature in darkness.
Protective Role of Thidiazuron Treatment on Cucumber
Seedlings Exposed to Heavy Metals and Chilling
A. S. Lukatkin, D. I. Bashmakov, and N. V. Kipaikina
Department of Botany and Plant Physiology, Mordovian State University, Bol’shevistskaya ul. 68, Saransk, 430000 Russia;
Received October 29, 2001
—The action of thidiazuron, a synthetic growth regulator, was studied on 7-day-old cucumber seed-
L., cv. Monastyrskii) exposed to chilling and sublethal concentrations of lead and copper
ions. The extent of injury was assessed from the electrolyte leakage from cotyledonary leaves into distilled
water. Separate application of each stress factor induced an increase in membrane permeability; however, their
combined application caused a weaker response. A preliminary treatment of seedlings with thidiazuron fully or
partly prevented the stress-induced stimulation of electrolyte leakage from cotyledon segments. It is concluded
that thidiazuron elevates plant resistance to adverse environments.
Key words: Cucumis sativus - chilling temperatures - heavy metals - thidiazuron - membranes - electrolyte leak-
age - resistance
: II—index of injury.