Structure and ultrastructure of leaf and calyx glands in Galphimia brasiliensis (Malpighiaceae)

Abstract

The present study describes the anatomical structure of calyx and leaf glands in Galphimia brasiliensis and analyzes the mechanism of secretion. The glands are marginal and suprabasal, cup-shaped, sessile, and scarcely visible with the naked eye. Light microscopy reveals the following features: a thin, smooth cuticle; unistratified secretory cells; subglandular parenchyma; and vascular bundle supply composed of phloem and xylem with abundant druses of calcium oxalate. Transmission electron microscopy reveals the presence of secretory cells with conspicuous nuclei, dense cytoplasm, lipid droplets, numerous vesicles, mitochondria, Golgi, rough endoplasmic reticulum (RER), and elongated plastids with osmiophilic contents. The secretion reaches the apoplastic space and accumulates beneath the cuticle. Finally, the viscous, translucent exudate is eliminated by mechanical rupture of the cuticle. Histochemical analysis confirms that lipids are the main constituent. Small amounts of polysaccharides were also identified.

Leaf glands of Banisteriopsis muricata (Malpighiaceae): distribution, secretion composition, anatomy and relationship to visitors

“…The morphoanatomical similarity and analogous position between EFNs and elaiophores in Malpighiaceae indicate that these two secretory structures are homologous (Anderson 1990). Although the leaf glands of Malpighiaceae have been described as EFNs because of the predominance of secretion rich in sugars (Anderson 1990;Possobom et al 2010), lipids were also identified in the secretion of leaf glands of Galphimia brasiliensis (Castro et al 2001). This evidence supports the hypothesis of homology between EFNs and elaiophores and the importance of these secretory structures to understanding aspects of the phylogenetic relationships of Malpighiaceae (Castro et al 2001).…”

“…observed in other species of Malpighiaceae (Castro et al 2001;Machado et al 2008). The occurrence of eglandulated leaves and leaves with two to four pairs of glands in the basal third of leaf blade and petiole have been previously described for B. muricata (Gates 1982), but this was not exactly the pattern found in the present study.…”

“…Thus, the leaf glands of B. muricata can be considered extrafloral nectaries (EFNs) and the secretion as nectar. Moreover, the absence of lipids in the secretion dismisses the possibility of these leaf glands acting as elaiophores, as suggested by Castro et al (2001). These authors identified lipids in the secretion of the leaf glands of Galphimia brasiliensis by histochemical tests, but they did not provide images and so these results can not be verified.…”

“…Similar morphology has been observed in the leaf glands of other species of Banisteriopsis (Machado et al 2008;Araújo & Meira 2016), but in yet others the leaf glands are sessile (Machado et al 2008). The leaf glands of Banisteriopsis muricata possess a secretory surface that is restricted to the central region of the gland, which is common in some species of Banisteriopsis (Araújo & Meira 2016) and Galphimia brasiliensis (Castro et al 2001), but not in other Malpighiaceae, such as Peixotoa reticulata (Machado et al 2008).…”

“…Despite the great morphological diversity and the associated taxonomic and ecological value assigned to leaf glands in Malpighiaceae (Elias 1983), anatomical studies have been restricted to certain genera such as Banisteriopsis (Araújo & Meira 2016), Heteropteris, Peixotoa (Machado et al 2008), Galphimia (Castro et al 2001) and Diplopterys (Possobom et al 2010). Moreover, aspects of the ontogenetic development of these leaf glands are unknown.…”