Plant Molecular Biology 53: 51–59, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.
Fructose-2,6-bisphosphate contents were increased in response to salt,
water and osmotic stress in leaves of Bruguiera gymnorrhiza by differential
changes in the activity of the bifunctional enzyme
, Nobutaka Hanagata
, Zvy Dubinsky
and Isao Karube
Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo
School of Bionics, Tokyo University of Technology, 1404-1 Katakura, Hachioji, Tokyo 192-
0982, Japan (
author for correspondence; e-mail email@example.com);
Faculty of Life Sciences, Bar-Ilan
University, Ramat Gan 52900, Israel
Received 13 November 2002; accepted in revised form 10 August 2003
Key words: Bruguiera gymnorrhiza, fructose-2,6-bisphosphate, 6-phosphofructo-2-kinase/fructose-2,6-bisphos-
phate 2-phosphatase, salt stress
The steady-state level of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphate 2-phosphatase (F6P2K/F26BPase)
transcript has been found to be raised in the mangrove Bruguiera gymnorrhiza treated with 500 mM NaCl for 6 h.
In the present study, we assayed both F6P2K/F26BPase activity and fructose-2,6-bisphosphate(F26BP) contents in
leaves of salt- and water-stressed B. gymnorrhiza. In the plants treated with 500 mM NaCl, no increase in transcript
level was observed after 1 day of treatment, while both the ratio between F6P2K and F26BPase activity (K/P ratio)
and leaf F26BP level were about two-fold higher than in control plants.
Several water stress-associated treatments, including 500 mM NaCl treatment for 6 h, 1 M mannitol treatment
for 6 h and dehydration treatment, resulted in increases in leaf F26BP level as compared with water-grown plants.
The raised levels of F26BP in osmotically stressed plants treated with NaCl and mannitol were accompanied with
increased transcript levels and subsequent increases in both F6P2K and F26BPase activities, while the increase
in F26BP levels in dehydrated plants was attributed to an increase in K/P ratio without an increase in transcript
levels. These results suggest that, although both treatments resulted in increases in F26BP levels, B. gymnorrhiza
differentially responds to osmotic stress and water stress.
Abbreviations: F6P2K, 6-phosphofructo-2-kinase; F26BPase, fructose-2,6-bisphosphate 2-phosphatase; F26BP,
Fructose-2,6-bisphosphate (F26BP) is a regulatory
metabolite which is an inhibitor of fructose-1,6-
bisphosphatase and an activator of 6-phosphofructo-
1-kinase, and plays an important role in controlling
carbohydrate metabolism in eukaryotic cells (Okar
and Lange, 1999). In plant leaves, F26BP contrib-
utes to the coordination of sucrose synthesis with rate
ﬁxation and the regulation of photosynthetic-
ally assimilated carbon partitioning between sucrose
and starch (Stitt, 1990). Several studies of transgenic
plants have revealed that an increase in the level of
F26BP increases starch formation, whereas a decrease
in the level of F26BP increases sucrose formation
(Kruger and Scott, 1994; Scott et al., 2000; Draborg
et al., 2001).