1021-4437/04/5102- © 2004
Russian Journal of Plant Physiology, Vol. 51, No. 2, 2004, pp. 189–193. Translated from Fiziologiya Rastenii, Vol. 51, No. 2, 2004, pp. 211–216.
Original Russian Text Copyright © 2004 by Izmailov.
Nitrate penetrating the plant cell partitions between
the two compartments, the cytosol and vacuole (corre-
spondingly, metabolic and storage pools) [1, 2]. Both
direct and indirect assays of nitrate concentrations in
these compartments demonstrated that nitrate was pre-
dominantly stored in the vacuole [3–8]. However,
nitrate reductase is located in the cytosol [2, 9, 10].
Therefore, the investigation of the interaction between
metabolic and storage nitrate pools is important for
understanding the control of NR activity. This can help
to exploit the entire plant potential in the efﬁcient
nitrate consumption and to escape its excessive accu-
mulation in crops.
Despite the 30-year-long period of studying these
topics, the mechanisms of the interaction between met-
abolic and storage pools, the nature of their genetic
determination, and their dependence on various abiotic
factors are still poorly studied. A general conclusion
from performed investigations was that the rates of
nitrate inﬂux into and especially efﬂux from the vacu-
ole were much slower than the rate of nitrate exchange
in the metabolic pool . However, different crops
evidently differ in these indices.
The goal of this work was to study the kinetic and
functional characteristics of the saturation and exhaus-
tion of metabolic and storage nitrate pools in two crops,
pea and sugar beet, differing in the type of their metab-
olism (protein and carbohydrate metabolism, respec-
tively) and in their salt-tolerance.
MATERIALS AND METHODS
Experiments were performed with the second leaves
of pea plants (
L., cv. Ul’yanovskii 68)
and the ﬁrst true leaves of sugar beet plants (
L., cv. Yaltushkovskii). In peas, second leaves
appeared at the age of 7–8 days and wilted at the age of
20–24 days. In sugar beet plants, ﬁrst leaves appeared
on day 12 and grew for a month. Plants were grown in
the controlled chambers at a temperature of 22/20
(day/night), an illuminance of 15–20 klx from xenon
lamps, and a relative humidity of 70%. Plants were
grown in water culture in 6-l vessels (100 pea and
84 sugar beet plants per vessel).
To study the dynamics of nitrate uptake, 5.5-day-old
pea plants (from the moment of seed soaking in water)
and 14.5-day-old sugar beet plants (which were grown
on water for 6 days and then on the Knop solution con-
taining 0.1 mM KNO
) were transferred to the Knop
solution containing 4.2 mM , i.e., one-third of its
content in full Knop solution, at 8:00 p.m. (the shortage
was compensated with equimolar con-
centrations of K
). Plants were kept on
this solution during the entire experimental period.
Sampling was performed at 10:00 a.m. In experiments
Saturation and Utilization of Nitrate Pools
in Pea and Sugar Beet Leaves
S. F. Izmailov
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 May 5, 2002
—The critical periods in the saturation of pea and sugar beet leaves with nitrate absorbed by roots
were discriminated. In peas, during the ﬁrst 14 h, all nitrate penetrating leaf cells was concentrated in the cytosol
(metabolic pool). During the second period (14–62 h), nitrate began to ﬂow into the vacuole (storage pool), and
the ﬁlling of the metabolic pool continued. Metabolic pool was saturated by the end of this period (62 h). During
the third period (62–110 h), further nitrate accumulation in the cell occurred because of expanding of the stor-
age pool. Its saturation (similarly as total cell saturation) commenced 86 h after the start of nitrate uptake. In
sugar beet leaves, both metabolic and storage nitrate pools were saturated by the end of the ﬁrst period (14 h),
and the sizes of these pools did not change during the second period (14–86 h). When pea plants were trans-
ferred to the nitrate-free medium, nitrate efﬂux began from the storage pool until its complete exhausting after
3 days. In sugar beet leaves, nitrate was still present in the storage pool 4 days after plant transfer to the nitrate-
free medium. In both crops, nitrate export from the storage pool was aimed at the maintenance of the optimum
nitrate concentration in the metabolic pool and, thus, at the maintenance of nitrate reductase activity. A func-
tional diversity of nitrate compartmentation in the cells of various plant species is discussed.
Key words: Pisum sativum - Beta vulgaris - nitrate reductase - metabolic and storage nitrate pools
: NR—nitrate reductase.