ISSN 1021-4437, Russian Journal of Plant Physiology, 2006, Vol. 53, No. 1, pp. 110–115. © MAIK “Nauka /Interperiodica” (Russia), 2006.
Published in Russian in Fiziologiya Rastenii, 2006, Vol. 53, No. 1, pp. 122–127.
Proline is known to play an important role as an
osmoprotectant in plants subjected to hyperosmotic
stresses such as drought and salinity . Many studies
on proline synthesis and catabolism genes have shown
diverse functions of proline as a source of energy, nitro-
gen and carbon, and as an osmolyte in response to
dehydration [2–5]. Proline is synthesized via two routes
from either glutamate (Glu) or ornithine [1, 6]. It has
been demonstrated that the Glu pathway is predomi-
nant under the conditions of osmotic stress . In
, the ﬁrst two steps of the
proline biosynthesis from Glu are catalyzed by
line-5-carboxylate synthetase (P5CS), a bifunctional
enzyme with activities of
-glutamyl kinase (GK) and
Glu-5-semialdehyde (GSA) dehydrogenase (or
tamyl phosphate reductase, [7, 8]). In tomato plants,
there are two
loci in the nuclear genome: one spec-
iﬁes a bifunctional P5CS (tom
) and the other one
) apparently encodes a polycistronic mRNA
that directs the synthesis of GK and GSA dehydroge-
nase as two separate peptides . Two
present in both
and alfalfa plants [8, 10, 11].
gene expressed in most organs is
induced rapidly by stress [5, 8, 10].
in dividing cell cultures and its induction by stress is
dependent on protein synthesis .
Proline metabolism in bacteria has been studied in
detail . In
, conversion of Glu to Pro
is mediated by the sequential action of three enzymes
(Fig. 1), namely GK (ATP: L-glutamate 5-phospho-
-glutamyl phosphate reductase (L-
glutamate 5-semialdehyde NADP
P5CR (L-proline: NAD(P)
5-oxidoreductase) [1, 12].
These enzymes are the products of loci
organized into an operon. [13, 14]
Osmotins are a group of cationic proteins that exist in
at least two forms, with the isoelectric points of 7.8 and
8.2. They also differ slightly in molecular weight .
One of these forms, Osmotin-1, is water-soluble and
the other one, osmotion-11, is water-insoluble osmotin
synthesized as a proprotein with the molecular weight
of 26 kD. The molecular weight of the mature form is
24 kD . Osmotin is accumulated in vacuolar inclu-
sion bodies in the cells adapted to NaCl . It is local-
ized also in the cytoplasm at much lower levels  and
is loosely associated with isolated plasma membrane
and tonoplast vesicles .
Based on amino acid sequence and similarities in
pattern of expression, osmotin has been classiﬁed as a
member of PR-5 type proteins of tobacco plants. These
Comparison of Bacterial and Plant Genes Participating in Proline
Gene, with Respect to Enhancing
Salinity Tolerance of Transgenic Tobacco Plants
A. Sokhansanj*, S. A. Sadat Noori**, and V. Niknam*
*Department of Biology, Faculty of Sciences, University of Tehran, Tehran, 14155-6455, Iran
**Department of Agronomy and Plant Breeding, Abouraihan Campus, University of Tehran, Iran
Received April 25, 2005
—In an attempt to increase tolerance to salinity stress in tobacco plants, the genes encoding the mutant
form of glutamyl kinase (
), pyrroline-5-carboxylate synthetase, and osmotin were cloned into three differ-
ent shuttle vectors and were separately introduced into the tobacco plants. The transgenic lines were compared
for their ability to produce shoots and grow in MS medium containing 320 mM NaCl; it was shown that the
transgenic lines containing genetically handled
gene are more resistant to salinity. The amount of chlo-
was used to show continuing growth of plant lines. The results showed that only the tobacco lines
transformed with the modiﬁed
gene exhibited greater tolerance to salinity.
Key words: Nicotiana tabaccum - salt stress - salinity tolerance - glutamyl kinase - pyrroline-5-carboxylate
synthetase - transgenic plants - osmotin
: BA—benzyladenine; GK—glutamyl kinase;
Glu—glutamate; GSA—Glu-5-semialdehyde; MS—Murashige
and Skoog nutrient medium; P5CS—
The text was submitted by the authors in English.