Ultrastructural changes in the primordia of juice sacs of satsuma mandarin fruits

Ultrastructural changes in cells of developing juice sac primordia at anthesis and 19 days after anthesis in citrus fruits, satsuma mandarin (Citrus unshiu Marc.), were studied by light and transmission electron microscopy, to further explore the question of the pathway for transport of solutes into juice sac. The distribution density of plasmodesmata in the walls of juice sac cells increased markedly during the first 19 days after anthesis. During the same period plasmalemma invaginations developed and multivesicular bodies were seen in the invaginations of the tonoplast membrane protruding into the vacuoles. These developed most commonly in the basal portion of juice sac. Plasmalemmasomes in juice sac cells were also seen. These features of juice sac cells show the possibility of two pathways for translocation of solutes, one via plasmalemma-vesicles to vacuoles, the other through plasmodesmata.