Using various cytochemical techniques, the author has studied the way in which mucilage is secreted by the trichomes of
Psychotria bacteriophila. As in all cells specialized for the secretion of mucilage, the dictyosomes play the most important role.
However, their functioning in these cells is rather remarkable since they do not produce large secretory vesicles. The fenestrated cisternae on the secretory face bud small vesicle which open in the periplasm. Then the polysaccharide secretion condenses. More or less complete lysis of the cell wall then allows the mucilage to migrate to the outside of the trichome.
In contrast with what happens in other mucilage-secreting cells, the endoplasmic reticulum plays a part in the secretory process, since it produces a protein fraction which, after expulsion from the cytoplasm, associates itself with the polysaccharide fraction.
The trichomes are thus, in fact, the site of a twofold secretion; of polysaccharides (and perhaps of glycoproteins) in the dictyosomes, and of proteins in the cisternae of the endoplasmic reticulum.
They produce, then, a complex kind of mucilage which constitutes a veritable culture medium for the symbiotic bacteria.
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