Development and differentiation of the extrafloral nectaries from flower buds in Vigna luteola (Leguminosae, Phaseolinae)

Abstract

To study the ontogeny of the extrafl oral nectaries present in the infl orescences of Vigna luteola (Jacq.) Benth (Leguminosae, Phaseolinae), the location, morphology, anatomy of the earliest stages, histology of the defi nitive structures and ultrastructure of the secretory stage were analyzed. The extrafl oral nectaries at different developmental stages were examined with light microscopy and scanning electron microscopy. The secretory stage was also examined with transmission electron microscopy. The racemose infl orescence of V. luteola has six nodes. At each node, a short globose secondary axis bears two fl owers and one to three extrafl oral nectaries. Each extrafl oral nectary originates from the abscission of a fl ower bud and is formed by two differentiated zones: a ring of epidermal cells surrounding a group of longitudinally enlarged papillose central cells, both with underlying secretory parenchyma. The primary secretory tissue consists of the central cells, while the ring contributes to secretion to a lesser degree. Secretion is granulocrine, by means of exocytotic vesicles and plasmalemma invaginations. Four developmental stages succeed; the third one being the secretory. The extrafl oral nectaries activity period starts when the fl owers of the same secondary axis open and ceases before fruit development.