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

In order to change the sugar status during seed development a yeast-derived invertase gene was expressed in cotyledons of Vicia narbonensis. As a result, sucrose decreased whereas hexoses accumulated. We analysed cell structure and cellular differentiation in cotyledons expressing the yeast-invertase. Transgenic cells contained large and long-persisting vacuoles apparently serving as storage compartments for hexoses and clusters of storage-protein aggregates. In the wild-type, large vacuoles did not persist but were replaced by smaller protein bodies. During maturation and desiccation, the transgenic cells showed plasmolysis and vesiculation of the endo-membrane system. Immunogold-labelling revealed that the storage proteins vicilin and legumin were present within the cytoplasm and the extraprotoplasmic space and were attached to membranes of the endoplasmic reticulum and the nuclei. Protein storage vacuoles in mature seeds appeared heterogeneous and only partially filled. The data suggest that sugars control the subcellular organisation of the vacuolar system. Transcript levels encoding a tonoplast intrinsic protein, a marker for membranes of protein storage vacuoles, remained unchanged whereas mRNA levels of a hexose and a sucrose transporter increased. Generally, transgenic seeds appeared to be physiologically younger than wild-type seeds of the same age. The data underline the important role of sugars in legume seed development.