Ultrastructural studies on the secretory cavities ofCitrus deliciosa ten. I. Early stages of the gland cells differentiation

Summary Secretory cavities ofCitrus deliciosa seem to originate from a pair of meristematic cells (an epidermal cell and a second one placed under it). These cells undergo successive divisions resulting in the formation of a globular/oval gland situated in the parenchyma, and a conical stalk, which joins the gland with the epidermis. The young gland consists of a central group of polyhedral cells ensheathed by layers of radially flattened cells.During the early differentiation stages of the gland cells a close association of cytoplasmic microtubules with various organelles is observed. Plastids increase progressively in number and size and their matrix locally contains tubular networks accompanied by small oil droplets. In peripheral cytoplasm numerous myelin-like lomasomes have been observed. Peripheral cells of the gland are gradually modified from the inner cells following a different developmental pattern. Their walls become thicker and plastids do not contain tubular complexes, but only a few thylakoids partly surrounding the newly formed starch grains.