1021-4437/03/5004- $25.00 © 2003
Russian Journal of Plant Physiology, Vol. 50, No. 4, 2003, pp. 441–443. Translated from Fiziologiya Rastenii, Vol. 50, No. 4, 2003, pp. 496–498.
Original Russian Text Copyright © 2003 by Pustovoitova, Drozdova, Zhdanova, Zholkevich.
Although the impact of drought on physiological
processes has been under study for a long period, with
numerous data collected, the time-course of the
changes in the leaf growth rate and the rate of photosyn-
thesis was never related explicitly to water deﬁcit pro-
gression. Many researchers still cling to the notion that,
in addition to ABA accumulation, growth arrest under
drought conditions is caused by a decline in the rate of
photosynthesis, because photosynthesis is the physio-
logical process most sensitive to moisture deﬁcit .
Meanwhile, this idea has been confuted already in the
classic studies by Maksimov  and Alekseev .
Our goal was to place the deceleration of leaf
growth arrest and the inhibition of photosynthesis in the
succession of events observed under the progressive
soil drought and to correlate growth suppression with
leaf phytohormone contents.
MATERIALS AND METHODS
Cucumber plants (
L., cv. Nezhin-
skie) were grown in a phytotron chamber under ﬂuores-
cent light (40 W/m
, a 16-h photoperiod) at 21–23
Plants were grown in pots containing 350 g of dried
soil. The control plants were watered daily to 70% of
ﬁeld water capacity (MWC). Drought was imposed by
the cessation of watering on day 17 after seedling emer-
gence, when the ﬁrst leaf has developed almost com-
pletely, and the second leaf was rapidly expanding (leaf
area of about 45 cm
). The second leaf was the subject
for our study. Its growth was assessed by the changes in
the leaf dry weight and area and by the length of the
The rate of carbon dioxide ﬁxation was determined
in the same attached leaves using a gasometric open
system in series with an Infralyt-3 infrared gas analyzer
(Junkalor, Germany) at 0.03% CO
leaf in an exposure chamber was illuminated at the sat-
urating irradiance of 2240
s). A TN-10-60T
turgorometer with a scale factor of 0.01 mm was used
to measure leaf thickness .
Phytohormone contents were determined by an
immunoenzymic method ; transpiration rate, by
weighing ; and the total moisture content, by weigh-
ing leaves after drying at 105
Four experiments were run, and their results were
compatible. Below we give the data from a typical
experiment. Measurements were replicated 4–10 times,
with assays repeated three times in each replication.
The data in the ﬁgures are means and their standard
The cessation of watering produced the gradual pro-
gressive soil drought. In seven days, soil moisture con-
tent dropped down from 70.0 to 28.8% MWC (Fig. 1a).
By the end of the experiment, the control plants devel-
oped three leaves and those subjected to drought, only
two leaves. Thus, drought evidently repressed leaf
growth in plants. In plants subjected to drought, the sec-
ond leaf maintained its turgor up to the day 6. The sec-
ond leaf thickness in the control and droughted plants
0.01 and 0.18
0.01 mm, respectively. On
the day 7, the second leaf of the droughted plants
wilted, and its thickness diminished to 0.17
0.01 mm in the control plants (this dif-
ference was signiﬁcant at
0.05) (Fig. 1h).
Leaf Growth, Photosynthetic Rate, and Phytohormone Contents
Plants under Progressive Soil Drought
T. N. Pustovoitova, I. S. Drozdova, N. E. Zhdanova, and V. N. Zholkevich
Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, 127276 Russia;
fax: 7 (095) 977-8018; e-mail: email@example.com
Received June 7, 2002
—Effects of progressive soil drought on leaf growth, the rate of photosynthesis, and phytohormone
contents were followed in the experiments with cucumber (
L.) plants. Suppression of photo-
synthesis by drought did not immediately cause growth retardation, because the latter was observed one day
earlier than the inhibition of photosynthesis. In the meantime, growth retardation could be caused by a decline
in IAA and cytokinin contents, rather than ABA accumulation, because ABA accumulated when the growth has
been already suppressed.
Key words: Cucumis sativus - growth - photosynthesis - phytohormones - drought
: MWC—maximum soil water capacity.