1021-4437/04/5106- © 2004
Russian Journal of Plant Physiology, Vol. 51, No. 6, 2004, pp. 769–773. Translated from Fiziologiya Rastenii, Vol. 51, No. 6, 2004, pp. 855–859.
Original Russian Text Copyright © 2004 by Kabachevskaya, Lyakhnovich, Volotovskii.
The process of signal transduction in cells is gener-
ally represented simplistically as a linear chain of
sequential events initiated by the interaction of an
external factor with a cell receptor and ending in a bio-
logical effect proper. Simplistically, signals are trans-
duced in cells in such a way that one signal (of physical
or chemical nature) corresponds to one signal chain.
Such relationship applies to the transduction of phyto-
hormone effects in plants, such of auxin, gibberellin
and cytokinin. In fact, the relationships between vari-
ous signal chains are rather complicated; it allows plant
to respond to numerous changes in the internal and
environmental conditions and provide for ﬁne adjust-
ment in cell homeostasis . Transduction of phytohor-
mone and light signals is an example. The studies of
functions of many phytohormone classes demonstrated
their effect on photomorphogenetic responses. For
example, transferring to darkness of light-grown
the endogenous concentration of abscisic acid, due to
release of inhibitory control of phytochrome, red light
(RL) photoreceptor, on cell phytohormone content .
Phytochrome also controls phospholipase D (PLD)
activity . In its turn, PLD is involved in ABA-signal-
ing in plant cell [4, 5]. In view of the fact that ABA
metabolism and PLD activity are regulated by light, it
seems reasonable to examine the potential relationships
between these systems. In addition, the effect of other
phytohormones on PLD activity mediated by the activ-
ity of phytochrome system  remains virtually unex-
plored. Hence, we studied the effect of IAA, GA, and
cytokinin on photoregulation of PLD activity.
MATERIALS AND METHODS
L.), cultivar Bug, seedlings, were
grown for four days at 25
C on ﬁlter paper moistened
with tap water. The seedlings were grown in darkness
or in the light in a luminostat under ﬂuorescent lamps
(ﬂux rate at the plant level was 20 W/m
, light period
was 12 h).
The effect of ABA and RL on PLD activity in eti-
was studied by the radiolabel
method. The label was introduced into membrane lipids
of oat seedlings by incubating lipid preparation (150 mg)
for 24 h in 100
l of a solution, containing 0.5 MBq
inorganic orthophosphate (
). Phospholipase activity
was assayed by measuring transphosphatidylation reac-
tion, PLD-catalyzed transfer of phosphatidyl group
from phospholipid to primary alcohol, ethanol, with the
formation of phosphatidylethanol (PEt) . Transpho-
sphatidylation reaction was initiated by adding 1% eth-
anol to oat seedlings preloaded with the radiolabel.
Along with ethanol, ABA was added to the seedlings,
and latter were incubated for 1 h. Some seedlings were
irradiated with RL (
= 660 nm, 9 W/m
). The reaction
was discontinued by adding 600
l of chloroform :
methanol : HCl (100 : 100 : 1, v/v) mixture to the seed-
lings and freezing the sample in liquid nitrogen. Lipids
were extracted from plant tissues by the method of
Bligh and Dyer .
Lipid extracts were dried under argon ﬂow. The
qualitative analysis of the lipid extract was carried out
Regulation of Phospholipase D Activity by Light
and Phytohormones in Oat Seedlings
E. M. Kabachevskaya, G. V. Lyakhnovich, and I. D. Volotovskii
Institute of Biophysics and Cell Engineering, National Academy of Sciences,
Akademicheskaya ul. 27, Minsk, 220072 Belarus;
fax: 375-172-842359; e-mail: email@example.com
Received March 5, 2004
—The effect of synthetic analogs of phytohormones and red light absorbed by phytochrome on the
phospholipase D activity (PLD) was studied in oat (
L.) seedlings. ABA manifested a short-term
stimulating effect on PLD activity in the green seedlings and inhibited phospholipase activity in the etiolated
plants. Kinetin inhibited enzyme activity in the etiolated seedlings and did not affect its activity in light. GA did
not markedly affect PLD activity in the etiolated plants and activated this enzyme in the green seedlings.
Finally, IAA did not affect the enzyme activity. The relationship of the regulatory effects of phytohormones and
light on PLD activity is discussed.
Key words: Avena sativa - phospholipase D - phytohormones - red light
: Kin—kinetin; PC—phosphatidylcholine; PE—
phosphatidylethanolamin; PEt—phosphatidylethanol; PG—phos-
phatidylglycerol; PLD—phospholipase D; RL—red light.