Rapidly-secreting,cultured oat cells serve as a model system for the study of cellular exocytosis. Characterization of cells and isolated secretory vesicles

Summary Callus-derived suspension cultures of oats dramatically increase the viscosity of the culture media after one month in culture. Colorimetric assays for sugars and protein, as well as measurements of viscosity, suggest that the released material is a long-chain polysaccharide, probably a pectinaceous substance. These cells grow slowly in liquid culture, yet despite their low cell density, they are able to increase the viscosity of the media several fold within seven days after media transfer. Ultrastructural observations show that oat cells have features common to actively-secreting cells; especially evident are numerous dictyosomes with hypertrophied cisternae. Using a combination of filtering and centrifugation techniques we were able to recover large numbers of intact secretory vesicles. The interior of the vesicles stain with periodic acid-silver hexamine, and colormetric analysis of the vesicle pellet for total sugars confirms the presence of polysaccharides in this vesicle fraction. Because of the uniformity of these cells, the high rate of secretion, and the accessability of a large vesicle population, this culture system is'a useful model for studying the secretory process in plant cells.Scientific Article No. A-3128, Contribution No. 6196 of the Maryland Agricultural Experiment Station, College Park, MD.