1021-4437/02/4901- $27.00 © 2002
Russian Journal of Plant Physiology, Vol. 49, No. 1, 2002, pp. 68–73. Translated from Fiziologiya Rastenii, Vol. 49, No. 1, 2002, pp. 78–84.
Original Russian Text Copyright © 2002 by Pavlinova, Balakhontsev, Prasolova, Turkina.
Sucrose is widely spread in plants; it is formed in
leaves during photosynthesis as a primary free sugar
and is used as a transportable substance for export to
sink organs [1, 2]. The pathways of enzymatic sucrose
synthesis are well studied. However, the intracellular
location of the enzymes responsible for synthesis and
degradation of sucrose has not yet been determined.
The physiological signiﬁcance of the individual
enzymes also remains unclear.
Synthesis and subsequent conversions of the disac-
charide involve the following enzymes:
(1) Sucrose-phosphate synthase (UDP-glucose:D-
22.214.171.124) catalizes a reaction that is actually irrevers-
UDPG + fructose-6-phosphate
sucrose-6-phosphate + UDP.
Subsequently, sucrose phosphatase (EC 126.96.36.199)
catalizes a reaction:
Sucrose-6-phosphate + H
O sucrose + P
(2) Sucrose synthase (UDP-glucose:D-fructose-2-
-glucosyltransferase, EC 188.8.131.52) catalyzes a revers-
UDPG + fructose sucrose + UDP.
(3) Invertase (
-D-fructofuranosidase, EC 184.108.40.206)
hydrolizes sucrose to glucose and fructose:
sucrose + H
O glucose + fructose.
In this work we focused on the role of each enzyme
in relation to plant age and on the role of these enzymes
in individual leaves during the leaf development and
sink–source transition. Studying the enzyme activities
under the action of external and internal factors may be
important for understanding the ways of regulating and
enhancing sugar accumulation in sugar beet plants.
MATERIALS AND METHODS
To study the diurnal course of enzyme activities in
the middle-layer leaves (leaves expanded to 80–90% of
their ﬁnal surface area) and in leaves of different ages,
we used 70-day-old sugar beet plants (
cv. Verkhnyacheskaya 031) grown in pots with soil.
Changes in enzyme activities during plant growth and
development were monitored in experiments with a
beet cultivar Yaltushkovskaya odnosemennaya, grown
Sucrose-Phosphate Synthase, Sucrose Synthase,
and Invertase in Sugar Beet Leaves
O. A. Pavlinova*, E. N. Balakhontsev**, M. F. Prasolova*, and M. V. Turkina*
* Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, 127276 Russia;
fax: 7 (095) 977-8018; e-mail: firstname.lastname@example.org
**Bashkir Research Center, Ural Division, Russian Academy of Sciences, Ufa, Bashkortostan, Russia
Received February 22, 2001
—The activity of sucrose-phosphate synthase (SPS) in sugar beet (
L.) leaves was shown
to exceed considerably the synthesizing activity of sucrose synthase (SS). The rise in SPS activity was related
to the daylight period; i.e., it was associated with the rate of photosynthesis. The highest SPS activity was char-
acteristic of fully expanded source leaves. In young developing leaves (leaves expanded to less than half of their
ﬁnal size), which represent the sink organs, the SPS activity was 2.5 times lower. At all stages of leaf develop-
ment, the synthesizing SS activity was rather low. The diurnal change of SS activity was independent of pho-
tosynthesis and showed a slight rise from 6:00–8:00 p.m. Under ﬁeld conditions, the highest SPS activity was
found in leaves in the terminal stage of their development (105-day-old plants); the synthesizing activity of SS
showed little changes during this period. The activity of soluble acid invertase was characteristic of young
leaves. In mature leaves, the activity of this enzyme correlated with the daylight period. These changes occurred
on the background of low sucrose content in leaves. The regulation of SPS, SS, and invertase activity is dis-
cussed. It is supposed that compartmentation of these enzymes in the photosynthesizing cell is important for
transport, metabolism, and the osmotic function of sucrose in leaves.
Key words: Beta vulgaris - sucrose - leaf - sucrose-phosphate synthase - sucrose synthase - invertase - func-
: SPS—sucrose-phosphate synthase; SS—sucrose
synthase; UDPG—uridine diphosphate glucose.