Abstract
Brazilian Savanna stands out for the large number of species with extrafloral nectaries (EFNs) with high morphological diversity. In Smilax polyantha (Smilacaceae), the base of the petiole showed a slight secretion and great visitation by ants suggesting the presence of an EFN. In this way, we aimed to determine the ant community associated with this plant, as well as to identify and characterize this unsuspected structure and determine the phenology and liquid production of this tissue. The study was carried out in a Cerrado area, in Uberlândia, Brazil. Ten individuals were used for the anatomical analysis and histochemical tests and the EFNs secretory activity was monitored, being categorized into active and non-active EFN. In addition, the volume and sucrose concentration were determined from three nectaries of ten individuals, and individuals of ants found foraging on these nectary were collected, day and night. Results showed a large amount of extrafloral nectar secretion and the EFN tissue is composed of a few cell layers that showed positive reactions for proteins and reducing sugars. We recorded a significantly correlation between percentage of EFNs activity and abundance of ants. The secretory activity is concentrated in September and ten ant species, of five subfamilies, were identified foraging on the EFNs.
Highlights
The base of the petiole is wrapped by an arc-shaped structure that has secretory tissue secreting nectar and intense visitation by ants (Fig 1A-B).This arc-shaped structure (Fig 1C) has a uniseriate adaxial epidermis displaying features typical of secretory cells, such as a thin cuticle and dense cytoplasm (Fig 1D)
The presence of an arc-shaped structure composed of adaxial epidermal cells with secretory features such as a thin cuticle and dense cytoplasm and underlying parenchyma with dense cytoplasm and conspicuous nucleus, together with the presence of sugars and proteins in these tissues and nectar-collecting activity exhibited by ants, show that the structure located in the petiole is an extrafloral nectaries (EFNs)
In the Cerrado, most of the known EFNs are elevated (Oliveira & Leitão-Filho, 1987; Machado et al, 2008), differing morphologically from those observed in S. polyantha
Summary
Tropical regions show a high diversity and distribution of plants bearing extrafloral nectaries (EFNs) (Oliveira & Leitão-Filho, 1987; Koptur 1992; Rico-Gray & Oliveira, 2007) and many of them are morphologically simple and composed of only a few layers of secretory cells (Machado et al, 2008). Escalante-Pérez and Heil (2012) have characterized the anatomy and ultrastructure of nectariferous tissue as a secretory epidermis and specialized nectariferous parenchyma that produces or stores the pre-nectar; the cells commonly have dense cytoplasm and a well-developed membrane system (Fahn, 1979; Nepi, 2007). EFNs are structures that produce a liquid substance, the extrafloral nectar, rich in carbohydrates andother diluted compounds (e.g. lipids, amino acids, etc.) (Baker & Baker, 1983; Koptur, 1994; González-Teuber & Heil, 2009), which attracts several arthropods for feeding (Marazzi et al, 2013) These arthropods, such as ants, can play an important role as biotic defenders of plants against herbivore attack (Rico-Gray & Oliveira, 2007; Heil, 2015).In return, there is a significant gain in survival and reproduction by extrafloral nectar feeding (Byk & Del-Claro, 2011)
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