The ovular integument of Pittosporum undulatum Vent.: Fine structural observations

Abstract

The single integument of the anacampylotropous ovule of Pittosporum undulatum Vent. (Pittosporaceae) has been investigated by light and electron microscopy. Three integumentary different regions have been detected: a peripheric layer, a parenchymatous outer region and an inner region. These may be distinguished in the medium antiraphe side on the basis of the cell shape, size and features. The cells of the peripheric layer facing the ovaric hollow appear different from the inner ones adjacent to the nucellar epidermis in their shape, for the thickness of their continuous cuticular layers and for the structure of the cell walls. The outer cells are also covered by an epicuticular layer and show the occurrence of plastids with starch grains, electron dense matrix and Light Stained Membranes. The same cells accumulate lipid bodies and a reserve of protein nature in cytoplasmic areas lacking ribosomes. The inner peripheric cells show thick inner periclinal walls characterized by a loose texture often containing flat sac-like structures. The outer integumentary region consists of parenchymatous cells with a high concentration of both carbohydrate and lipid bodies. On the other hand, the periclinally elongated cells which characterize the inner region show the ultrastructural features of scarcely differentiated cells. Such morphology of the tegumentary system has been also observed in anomalous ovules showing an arrested development of nucellus. They appear tenuinucellate and contain either a single megasporocyte or a linear tetrad of megaspores with an enlarged chalazal sporial cell.

Key words:

• Embryology
• Ovular integument
• Pittosporum undulatum
• ultrastructure