Anatomical and histochemical characterization of glands associated with the leaf teeth in Rhaphiolepis loquata B.B.Liu & J.Wen (Rosaceae Juss.)

Abstract

Several representatives of Rosaceae are characterized by presenting leaf teeth. These projections on the leaf margins may be associated with different secretory structures such as extrafloral nectaries, hydathodes or colleters. Colleters are the secretory structures far less kwon in Rosaceae. Although colleters were previously mentioned in species from subfamily Amygdaloideae, authors fail to provide a detailed morphoanatomical description and the chemical nature of the secretion for those colleters. Therefore, we aimed to morphoanatomically describe the leaf teeth of Rhaphiolepis loquata, confirming the nature of the gland associated with the teeth and shedding light on the chemical composition of the gland exudates. For that, samples from the leaf margins at different stages of development were collected and fixed according to standard techniques for both light and scanning electron microscopy. The leaf teeth in R. loquata presented a colleter at its apex. Colleters were rounded with covered by single- or doubled-layered secretory palisade covered with thick cuticle and the central axis was made up of parenchyma cells. The presence of polysaccharides, pectins and proteins was confirmed in the exudates and phenolic compounds accumulated as the gland aged and ceased the exudate production. An abscission zone at the base of the colleter was observed what could cause the falling off of older, non-secreting colleters. This is the first study on the chemical composition of colleter exudates as interpreted through histochemical tests, being a novelty not only for R. loquata but for the Rosaceae family.