Leaf colleters in Tabernaemontana catharinensis (Apocynaceae, Rauvolfioideae): structure, ontogenesis, and cellular secretion

Abstract

Colleters, which are glands that produce sticky secretion, have ecological and taxonomic relevance in Apocynaceae. We studied the distribution, morphology, ontogenesis, and cellular secretions of leaf colleters in Tabernaemontana catharinensis A.DC. Samples from mature embryos, seedlings, and plants were processed according to usual methods for anatomical, histochemical, and ultrastructural analyses. Colleters are non-vascularized emergences that occur on the adaxial face of expanded cotyledons, eophylls, and metaphylls and at the intrapetiolar and interpetiolar positions. Standard, bifurcate, trifurcate, and sessile colleters were found, and these glands did not differ in their ontogenesis, histochemistry, or histological composition. Golgi bodies, rough endoplasmic reticulum, and plastids filled with oil droplets were the predominant organelles in the epithelial cells. Mucilage accumulated in large periplasmic spaces, traversed the outer cell wall and the permeable cuticle, which remained intact. Senescent epithelial cells were characterized by signs of cell plasmolysis, organelle degradation, membrane vesiculation, and ruptured tonoplast. Ultrastructural changes in the cell wall strengthen the argument for the involvement of this cellular compartment in the exudates’ exit. We provide the first report of the occurrence of different types of colleters in a Rauvolfioideae member. Our ontogenetic data support the hypothesis that morphological variants are deviations from the standard type.