ENHANCEMENT OF SEED-GERMINATION IN HIGH SALINITY BY ENGINEERING MANNITOL EXPRESSION IN ARABIDOPSIS-THALIANA

The bacterial gene mtlD, which encodes mannitol 1-phosphate dehydrogen ase (E.C.1.1.1.17), was transformed into Arabidopsis thaliana and expr essed under control of the CaMV 35S promoter, MtlD-transformants accum ulated mannitol, a sugar alcohol that is not normally found in Arabido psis, Amounts of soluble carbohydrates, sucrose, glucose, fructose, my o-inositol and mannitol were determined in different tissues of wild-t ype and transgenic plants. We estimated that less than 1% of the carbo n assimilated was converted into mannitol by the transgenic plants. Th e establishment of individual transformed lines (after self-crossing t hree times) resulted in high and low mannitol-producing lines which we re stably maintained, The presence of mannitol did not alter plant app earance or growth habit. When MtlD-expressing seeds and control seeds (T3 generation) were imbibed with solutions containing NaCl (range 0 t o 400 mol m(-3)), transgenic seeds containing mannitol germinated in m edium supplemented with up to 400 mol m(-3) NaCl, while control seeds ceased germination at 100 mol m(-3) NaCl, It is doubtful whether the a bility to germinate in high salt was a result of an osmotic effect exe rted by elevated levels of mannitol, considering that mannitol concent rations were in the mol m(-3) range in seeds. A specific effect of pol yols, for example on the integrity of subcellular membranes or enzymes , cannot be excluded.