SOLUTE INCOMPATIBILITY WITH GLUTAMINE-SYNTHETASE IN WATER-STRESSED POPULUS-NIGRA

When poplar leaves were submitted to water-stress for 18 h (correspond ing to a 0.1 M mannitol application), the activity of glutamine synthe tase (EC 6.3.1.2) decreased by about 50%. The ability of several solut es accumulated by stressed poplars (glucose, putrescine, salicin, sper midine, sucrose, trigonelline) to affect in vitro the GS activity has been compared with that of some classical compatible solutes (mannitol , sorbitol, proline). Mannitol, salicin and trigonelline (in the range of 0.1-0.2 M) were drastic inhibitors of GS, while glucose and sucros e did not interfere with GS activity and might partially alleviate the inhibition of GS activity induced by mannitol in vitro. Proline and p utrescine (25 mM) were the most effective in alleviating the inhibitor y effect of mannitol; since a 0.2 M concentration of each one inhibite d GS, proline could not be referred to as a compatible solute. (C) 199 8 Elsevier Science B.V. All rights reserved.