Changes in Exudate Composition during the Development of the Ovary Glands in Aptenia cordifolia: I. The Quantitative Saccharide-Protein-Relations and the Protein Components

Summary Investigations on the exudate composition and the ultrastructure of the ovary glands in Aptenia cordifolia were carried out at different developmental stages to support the hypothetical secretion model for Saccharide-protein-secreting glands postulated by KRISTEN (1976). During the first 9 days after the beginning of secretion, the exudate composition shows only an insignificant change (polysaccharides 70-80%; mono-/ oligosaccharides 9-21%; proteins 4-6%). However, about 10 days after the beginning of secretion, the protein contents rises significantly to 24 °/o. This quantitative change of exudate composition is paralleled by the degeneration of the gland cells. In addition, the protein fraction of the exudate and of cell squashes taken at different developmental stages were analysed using gel electrophoretical separation. The results of these analyses suggest that at least two of the main protein components of the post-degenerative exudate must originate from the storage vesicle contents. The ultrastructure of the glands shows a high activity of the Golgi apparatus two days after the beginning of secretion. The contents of the numerous and rather big Golgi vesicles is extruded by exocytosis. Three days thereafter, vacuole-like storage vesicles which contain polysaccharides and proteins are also observable. These storage vesicles probably arise from fusion of Golgi vesicles, and, after formation, are ensheathed by cisternae of the rough ER. The Golgi apparatus, however, seems only to play an insignificant role in the intracellular transport of the proteins, as is demonstrated by comparisons of the compositions of exudates and of cell squashes in different developmental stages. The results o£ both exudate and ultrastructure analyses confirm the postulated secretion processes, which can be described as follows: (a) At the beginning of secretion predominantly polysaccharides are transported by Golgi vesicles and extruded via exocytosis, presumably accompanied by an eccrine secretion of mono- and oligosaccharides. (b) In a later stage, parallel to the granulocrine and eccrine secretion mentioned first, there is an accumulation of polysaccharides in the storage vesicles. The protein component is contributed to the storage vesicles presumably by their ensheathing rough ER. (c) Towards the end of secretion the protoplast degenerate, leading to a holocrine extrusion of the vesicle contents.