Ultrastructure of gum-resin secreting cells in the pith of Ailanthus excelsa Roxb.

The pith ducts of Ailanthus excelsa Roxb. (Simaroubaceae) secrete gum-resin. The synthesis of resin in the epithelial cells of the duct is associated with plastids and endoplasmic reticulum (ER) while dictyosomes are involved in the synthesis of the gum. In the secreting cells, large numbers of osmiophilic globules are scattered in the cytoplasm. Dictyosomes and ER produce abundant vesicles. The osmiophilic globules and vesicles fuse with the plasmalemma facing the duct lumen and are entrapped in plasmalemma invaginations. The walls of some of the epithelial cells have a few ingrowths which presumably enhance the efficiency of the cell in the transportation of materials from the cytoplasm. Some of the epithelial cells in a duct undergo autolysis and degeneration after secretion. The appearance of autophagic vacuoles containing portions of cytoplasm, the loss of tonoplast, the distortion of ER, mitochondria, dictyosomes and the darkening of cytoplasm are some of the autolytic features in the degenerating cells. The lysed cells with ‘dark’ cytoplasm, osmiophilic droplets and free ribosomes detach and disintegrate in the duct lumen, becoming part of the gum-resin content in the duct.