Ontogenetic, anatomical and histochemical study of the extrafloral nectaries of Sapium biglandulosum (Euphorbiaceae)

The present paper aims to confirm the nature of secretory structures found on the petiole and leaf margins of Sapium biglandulosum Müell. Arg. The anatomy, ontogenesis and histochemistry were studied by light microscopy, whereas mono- and disaccharides in the exudates were detected by high performance liquid chromatography. The exudate from the petiole had a total sugar concentration of 32.5% (w/v), of which 38.1% was fructose, 43.7% glucose and 18.2% sucrose. The petiolar gland started its development from a group of meristematic cells that underwent asynchronous divisions. At the end of the ontogenesis, a well structured vascularised gland made up of a palisade secretory epidermis, secretory parenchyma and a secretory pore was observed. Leaf-margin glands showed a similar anatomy. Histochemical tests revealed the presence of proteins, pectins, carbohydrates, tannins and anthocyanins. On the basis of our results, there is compelling evidence that the studied glands are in fact extrafloral nectaries.