Membrane structures in the integumentary cell walls of the ovule of Nerium oleander

Ultrastructural changes in the integumentary cell walls of Nerium oleander L. were observed, starting with the beginning of nucellus degeneration. The cell walls in direct contact with the nucellus, followed in a regular progression by those of the next 2-3 cell layers, were seen to increase rapidly in thickness and, in contact with the plasmalemma, to develop a peculiar layer characterized by the presence of numerous membrane-like structures. Morphological and cytochemical findings indicate a membraneous nature of these wall structures; the structures exhibit a marked affinity to potassium permanganate, ruthenium red and phosphotungstic acid, and possess a three-layered configuration. Moreover, the structures were found to be disorganized by phospholipase C. Some of the wall structures appear to be pitted, sac-shaped formations; others to be single sheets. Both types exhibit a direct continuity with the plasmalemma after digestion of the wall material by cellulase. The origin and development of these structures are discussed.