Ultrastructure and secretion of secretory canals in vegetative organs of Bupleurum chinense DC.

The development of secretory canals in vegetative organs of Bupleurum chinense DC. and the accumulation of essential oils were investigated by transmission electron microscopy (TEM) analysis. The secretion mechanism of the essential oil was also discussed. The results indicate that the plastid, ground substances of cytoplasm and mitochondria took part in the biosynthesis of oil or oil precursor. The endoplasmic reticulum involved in the transport of essential oil to the secretory lumen. At latter stages of development of secretory cells, numerous different sized vesicles fused with the plasmalemma along the boundary between two neighbor secretory cells and secreted the substance into the wall. Thus, the wall between two neighbor secretory cells near the lumen became loosely structured. Then, the wall lined the lumen near two neighbor secretory cells extruded numerous grey vesicles with various sizes on the side facing the lumen, and released these vesicles into the lumen. As a result, the manner of secretion in secretory canals of Bupleurum chinense DC. appeared to be exocytosis.