Ultrastructure of the epidermis of developing, ripening, and senescing navel oranges

Electron microscope studies revealed that throughout the development, maturation, and after-ripening of Navel orange fruits, the epidermal cells contained typical organelles. There were few significant changes in the ultrastructure of the organelles during these stages. However, there was considerable variation in the vacuoles, as well as changes in cytoplasmic inpockets and membranous configurations associated with the tonoplast, and changes in vacuolar content. These changes and variations probably indicate that the vacuoles have an important role as lysosomal compartments in accumulating and recycling cellular material during these stages. With early and late senescence there was a decrease in cytoplasmic organelles and a partial loss of membrane definition, indicating that metabolic dysfunctions associated with senescence may be related to the loss of compartmentation and the organizational integrity of the cells. Also with senescence, the vacuoles became filled with granular and lipid material, an indication that a reduction in the lytic and recycling capacity may have occurred. Dissolution of wall material also took place during this period. The final stage of degeneration was characterized by a loss of definition of membranes and organelles.