Plant Molecular Biology 43: 103–111, 2000.
© 2000 Kluwer Academic Publishers. Printed in the Netherlands.
Enhanced tolerance to salt stress in transgenic rice that overexpresses
chloroplast glutamine synthetase
, Yoshito Tanaka
, Takashi Hibino
, Yasuyuki Hayashi
, Akira Tanaka
and Teruhiro Takabe
Research Institute, Meijo University, Tenpaku-ku, Nagoya, Aichi, 468-8502 Japan (
author for correspondence;
Department of Chemistry, Faculty of Science and Technology, Meijo University,
Tenpaku-ku, Nagoya, Aichi, 468-8502 Japan;
Plantech Research Institute, Aoba-ku, Yokohama, Kanagawa, 227-
Graduate School of Bioagricultral Science, Nagoya University, Chikusa-ku, Nagoya, Aichi, 464-
Received 17 March 1999; accepted in revised form 16 March 2000
Key words: glutamine synthetase, photorespiration, rice, salt tolerance, transgenic plant
The potential role of photorespiration in the protection against salt stress was examined with transgenic rice plants.
Oryza sativa L. cv. Kinuhikari was transformed with a chloroplastic glutamine synthetase (GS2) gene from rice.
Each transgenic rice plant line showed a different accumulation level of GS2. A transgenic plant line, G39-2,
which accumulated about 1.5-fold more GS2 than the control plant, had an increased photorespiration capacity.
In another line, G241-12, GS2 was almost lost and photorespiration activity could not be detected. Fluorescence
quenching analysis revealed that photorespiration could prevent the over-reduction of electron transport systems.
When exposed to 150 mM NaCl for 2 weeks, the control rice plants completely lost photosystem II activity,
but G39-2 plants retained more than 90% activity after the 2-week treatment, whereas G241-12 plants lost these
activities within one week. In the presence of isonicotinic acid hydrazide, an inhibitor of photorespiration, G39-2
showed the same salt tolerance as the control plants. The intracellular contents of NH
in the stressed
plants correlated well with the levels of GS2. Thus, the enhancement of photorespiration conferred resistance to
salt in rice plants. Preliminary results suggest chilling tolerance in the transformant.
Accumulation of salts in irrigated soil are primary
factors depressing yield in crop production, because
the major crops are almost universally non-halophytic
(Yancey et al., 1982; Bohnert et al., 1995; Serrano,
1996; Volkmar et al., 1998). Organisms that thrive
in hypersaline environments possess speciﬁc mech-
anisms to adjust their internal osmotic status. One
such mechanism is the ability to accumulate low-
molecular-weight organic compatible solutes such as
sugars, some amino acids and quaternary ammonium
compounds, which are believed to be essential for
adaptability of plant cells to high salinity (Yancey
et al., 1982; Bohnert et al., 1995). Other mecha-
nisms of adaptation to high salinity are the exclusion
ions from the sodium-sensitive sites which
has been proposed as a function of a Na
tiporter and Na
ATPase (Serrano, 1996). Expression
of compatible solutes and heterologous sodium efﬂux
transporters may be a useful approach to improve the
salt tolerance of photosynthetic organisms. Indeed,
the increase of salt tolerance or water stress tolerance
of photosynthetic organisms transformed with genes
for synthesis of compatible solutes was demonstrated
(Tarczynski et al., 1993; Bohnert et al., 1995; Nomura
et al., 1995; Takabe et al., 1998).
In addition to these toxic effects, salt stress also
causes the induction of oxidative stress (Gossett et al.,
1994; Hernandez et al., 1995; Burdon et al., 1996).
Upon salt stress, stomatal closure triggeredby abscisic