Abstract
To study the ontogeny of the extrafloral nectaries present in the inflorescences of Vigna luteola (Jacq.) Benth (Leguminosae, Phaseolinae), the location, morphology, anatomy of the earliest stages, histology of the definitive structures and ultrastructure of the secretory stage were analyzed. The extrafloral 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 inflorescence of V. luteola has six nodes. At each node, a short globose secondary axis bears two flowers and one to three extrafloral nectaries. Each extrafloral nectary originates from the abscission of a flower 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 extrafloral nectaries activity period starts when the flowers of the same secondary axis open and ceases before fruit development.
Highlights
The extrafloral nectaries (EFNs) can be distinguished from the floral ones either for the position they occupy or their function. Caspary (1848) distinguished them for the position, naming “floral” those that are placed somewhere in a flower and “extrafloral” the ones located in vegetative structures. Delpino (1875) classified them according to their function, calling “nuptial” the ones involved directly in pollination and “extranuptial” the ones associated with other functions
The EFN of V. luteola originates from the abscission of a floral bud that stops its development. It consists of an elevation around the flower bud abscission scar, and corresponds to the “Hochnektarien” type according to the classification proposed by Zimmerman (1932), coinciding with what was observed in V. unguiculata (Ojehomon 1968), V. adenantha (Ojeda et al 2014), V. candida and V. caracalla (Ojeda et al 2015)
Díaz-Castelazo et al (2005) denominated “transformed nectaries” the EFNs that originate from transformation of an organ, including its abscission
Summary
The extrafloral nectaries (EFNs) can be distinguished from the floral ones either for the position they occupy or their function. Caspary (1848) distinguished them for the position, naming “floral” those that are placed somewhere in a flower and “extrafloral” the ones located in vegetative structures. Delpino (1875) classified them according to their function, calling “nuptial” the ones involved directly in pollination and “extranuptial” the ones associated with other functions. The extrafloral nectaries (EFNs) can be distinguished from the floral ones either for the position they occupy or their function. Caspary (1848) distinguished them for the position, naming “floral” those that are placed somewhere in a flower and “extrafloral” the ones located in vegetative structures. As there are intermediate situations, such as the ones on bracts, inflorescence rachis, or “outside” the flowers in the abaxial face of sepals, Schmid (1988) proposed the terms “reproductive” and “extra reproductive”. The “floral” and “extrafloral” denomination continues to be the traditional use (Bernardello 2007). Characterization of EFNs considering their morphology, and, in some instances, their origin was performed by Zimmermann (1931), commented and accepted by Elías (1983) and updated by Díaz Castelazo et al (2005)
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