Ultrastructural Study of the Development of Oil Cells in the Mesocarp of Avocado Fruit

The development of idioblastic oil cells in the mesocarp of avocado fruit was studied with the electron microscope. Observations concentrated on the formation of the complex cell wall and on the process of oil accumulation. The cell wall of the mature oil cells has three distinct layers: an external primary wall, a suberin lamella, and an interior tertiary wall No significant oil accumulation was observed until after the suberin layer was deposited and tertiary wall formation had begun. Formation of an extensive network of smooth tubular endoplasmic reticulum was observed concomitant with the initial accumulation of oil in the cytoplasm. In the latter stages of tertiary wall formation, the primary site of oil accumulation shifted from the cytoplasm to the vacuoles By the time the deposition of the tertiary wall was complete, most of the cell volume was occupied by a massive oil droplet; and the cytoplasm, which was devoid of membranes, was displaced to the cell periphery