Enhancement of seed germination in high salinity by engineering mannitol expression in Arabidopsis thaliana

Abstract

The bacterial gene mtlD, which encodes mannitol 1‐phosphate dehydrogenase (E. C. 1. 1. 1. 17), was transformed into Arabidopsis thaliana and expressed under control of the CaMV 35S promoter. MtlD‐transformants accumulated mannitol, a sugar alcohol that is not normally found in Arabidopsis. Amounts of soluble carbohydrates, sucrose, glucose, fructose, myo‐inositol and mannitol were determined in different tissues of wild‐type and transgenic plants. We estimated that less than 1& of the carbon assimilated was converted into mannitol by the transgenic plants. The establishment of individual transformed lines (after self‐crossing three times) resulted in high and low mannitol‐producing lines which were stably maintained. The presence of mannitol did not alter plant appearance or growth habit. When MtlD‐expressing seeds and control seeds (T3 generation) were imbibed with solutions containing NaCl (range 0 to 400 mol m−3), transgenic seeds containing mannitol germinated in medium 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 ability to germinate in high salt was a result of an osmotic effect exerted by elevated levels of mannitol, considering that mannitol concentrations were in the mol m−3 range in seeds. A specific effect of polyols, for example on the integrity of subcellular membranes or enzymes, cannot be excluded.