Morphoanatomy and development of leaf secretory structures in Passiflora amethystina Mikan (Passifloraceae)

Extrafloral nectaries (EFNs) are commonly found in Passiflora L. Reports have been made on the occurrence of resin-producing structures morphologically similar to EFNs in the genus. The objective of this study was to characterise the morphoanatomy and development of leaf secretory structures in Passiflora amethystina and to use chemical and histochemical tests to detect the presence of sugars in the exudates. Samples of leaf blade and petioles in different developmental stages were collected and subjected to usual techniques using light and scanning electron microscopy. Secretion samples were analysed by high performance liquid chromatography. The concentration of total sugars in the secretion amounted to 39.67% for blade EFNs and 52.82% for petiolar EFNs. EFNs consist of a secretory, uni- or bistratified palisade epidermis, arising from the protoderm by means of anticlinal and periclinal divisions, glandular parenchyma originated from the ground meristem, and xylem and phloem elements formed from the procambium. Exudate accumulated in a subcuticular space formed outside the epidermal cells from where it was then released. Histochemical tests showed a positive reaction for neutral polysaccharides. The results confirm that the leaf secretory structures are indeed extrafloral nectaries, and these findings constitute important information for studies on the taxonomy and ecology of this species.