STRATIFICATION OF STORAGE PROTEINS IN THE PROTEIN STORAGE VACUOLE OF DEVELOPING COTYLEDONS OF PISUM-SATIVUM L

Legumin, vicilin and pea albumin are the most prominent storage proteins in pea seeds. In order to localize these proteins in the developing cotyledons we have employed an improved fixation procedure for immunogold labelling for electron microscopy. Profiles of protein bodies (PB, 1-2 mu m diameter) label heavily and specifically with antibodies against vicilin and legumin. By contrast, such PB are only weakly labelled with antibodies against pea albumin 1. Antibodies against pea albumin 1 label a narrow, granulated zone at the luminal borders of the deposits. Depending on their size, storage protein deposits at the tonoplast of the protein storage vacuole (PSV) show different labelling patterns: small deposits label positively only with vicilin antibodies; labelling with legumin is seen in large deposits but is restricted to the tonoplast rather than luminal borders of the deposits. We frequently observed profiles of storage protein deposits at the tonoplast of the PSV, which were elongated and protruded into the cytoplasm. A gradient of legumin labelling in these deposits was seen. We interpret such images as stages in the formation of PB, which apparently arise by budding at the surface of the PSV.