Sugar levels altered by ectopic expression of a yeast-derived invertase affect cellular differentiation of developing cotyledons of Vicia narbonensisL.

In order to change the sugar status during seed development a yeast-derived invertase gene was expressed in cotyledons of Vicia narbonensis. As a resu lt. sucrose decreased whereas hexoses accumulated. We analysed cell structu re and cellular differentiation in cotyledons expressing the yeast-invertas e. Transgenic cells contained large and long-persisting vacuoles apparently serving as storage compartments for hexoses and clusters of storage-protei n aggregates. In the wild-type, large vacuoles did not persist but were rep laced by smaller protein bodies. During maturation and desiccation, the tra nsgenic cells showed plasmolysis and vesiculation of the endo-membrane syst em. Immunogold-labelling revealed that the storage proteins vicilin and leg umin were present within the cytoplasm and the extraproto-plasmic space and were attached to membranes of the endoplasmic reticulum and the nuclei. Pr otein storage vacuoles in mature seeds appeared heterogeneous and only part ially filled. The data suggest that sugars control the subcellular organisa tion of the vacuolar system. Transcript levels encoding a tonoplast intrins ic protein, a marker for membranes of protein storage vacuoles, remained un changed whereas mRNA levels of a hexose and a sucrose transporter increased . Generally, transgenic seeds appeared to be physiologically younger than w ild-type seeds of the same age. The data underline the important role of su gars in legume seed development.