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 6-phosphofructo-2-kinase/fructose-2,6-bisphosphate 2-phosphatase

The steady-state level of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphate2-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.