Abstract
Floral nectaries of Ocimum basilicum L. were studied using light, fluorescence and scanning electron microscopy. Each nectary forms an asymmetrical four-lobed disc at the base of the outer surface of the ovary. The three large lobes were found to be functional, whereas the smallest lobe is lacking in the modified stomata. Nectary anatomy is characterized by three major zones: a uniseriate epidermis, sub-epidermal secretory tissue and vascular tissue. The nectary epidermis of three functional lobes is covered with a very thin cuticle, and contains many modified stomata involved in the exudation process. They are diffusely distributed and lie in the same plane as the epidermal cells. The secretory tissue is composed of small cells with thin walls, relatively large nuclei, dense granular cytoplasm and small vacuoles. Most of the cells of the nectariferous tissue contain calcium oxalate crystals of different sizes. The nectary diameter, the size of the secretory cells and the thickness of the epidermis and cuticle increased during nectary ontogeny. The nectary is vascularized exclusively by phloem originating from vascular bundles destined for the gynoecium.
Highlights
Floral nectar is secreted by distinct glandular organs, the nectaries, whose anatomy and morphology vary greatly upon the taxon
The floral nectary is vascularized by phloem alone, originating from vascular bundles destined for the gynoecium
The floral nectary has the form of a prominent ring, encircling the base of the ovary (Figs. 1A, 2A and 3A)
Summary
Floral nectar is secreted by distinct glandular organs, the nectaries, whose anatomy and morphology vary greatly upon the taxon. These glands, which produce and secrete nectar may perform a vital function in sexual plant reproduction by attracting pollinators. Because the gland is usually well vascularized, its product may be basically regarded as a derivative of phloem sap. It is modified during the secretion process, which is a complex physiological accomplishment controlled by anthesis. It starts shortly before the flower unfolds (Vogel, 1983)
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