Morphoanatomy, histochemical and secretions process of extrafloral nectaries in Joannesia princeps Vell. (Euphorbiaceae).

• The acropetiolar glands of J. princeps are extrafloral nectaries (EFNs). • EFNs are anatomically similar to those described for other Euphorbiaceae. • Nectar is chemically complex including mainly fructose, besides polysaccharides, mucilage, and proteins. • Nectar exudation involves the subcuticular accumulation and cuticle disruption. Joannesia princeps presents two acropetiolar glands, with topography and morphology similar to extrafloral nectaries (EFNs). In the present study we described the anatomy and the ultrastructure of acropetiolar glands, and analyzed the histochemistry and chemical composition of secretion in order to (i) verify if these glands are nectaries and (ii) understand the complexity of secretion and the cell compartment involved with the production and exudation. The samples were processed according to the standard methodology for anatomical and ultrastructural studies. The gland has uniseriate epidermis composed by palisade secretory cells. The secretion produced by the secretory epidermis is accumulated in a subcuticular space, which causes distention of the cuticle until it be broken, allowing the exudation. Xylem and phloem vascularize the gland, with the phloem reaching the nectariferous parenchyma, even close to the secretory epidermis. The histochemical tests revealed polysaccharides, mucilage and protein in the secretion, whereas the exudate chemical analysis showed that glucose, fructose and sucrose are components of the nectar, being fructose the sugar predominant. The secretion is complex and different organelles are involved in this synthesis and secretion process. Secretory parenchyma cells presented a large peripheral nucleus, vacuole with granular material, conspicuous endoplasmic reticulum, numerous mitochondria, plastids, and plasmodesmata. During the secretion process, a granular material is accumulated into the vacuole, which merges with the plasma membrane of the secretory epidermis, releasing this material into the periplasmatic spaces. After crossing the cell wall of the epidermal cell, the secretion is accumulated in a subcuticular space, until ready to be released by the cuticle disruption. Based on this study, we can affirm that the glands of it are extrafloral nectaries. [Display omitted] [ABSTRACT FROM AUTHOR]