Ontogênese e mecanismo de secreção em coléteres de Morinda citrifolia L. (Rubiaceae)

Abstract

Colleters are structures secretory present in more than 60 families of angiosperms, whose function is protect the leaf primordium against physical and chemical damages. The colleters develop from cells of the fundamental meristem and of the protoderm, for differentiation and cellular reorganization for the development of the mature structure. After cell differentiation the secretory process begins. The Secretion is a complex phenomenon of synthesis, separation and isolation substances, as well as release or extracellular elimination. In this context, the external periclinal wall plays a fundamental role in the passage of secretion into the external environment. The colleters have mixed origin, developing from the protoderm and the fundamental meristem. These structures are present on the adaxial side of the stipules and have a morphology of the standard type. During development, the colleters of Morinda citrifolia L. (Rubiaceae) go through four stages of development defined by structural and anatomical changes: Undifferentiated, pre-secretory, secretory and senescent. At the undifferentiated stage, the secretory structures studied are characterized by small protuberances at the base of the adaxial surface of the stipules. In the pre-secretory stage, the epidermis begins its differentiation. In the following stages, the colleters present axis central parenchymatic covered by epidermal cells in palisade. The secretion is abundant at the vegetative apex impregnating the leaf primordium and stipules. Thus, the objective of this work is describe the ontogenesis of the coléteres of Morinda citrifolia, as well as the secretion mechanism using scanning electron microscopy techniques, light field microscopy (including histochemical tests) and laser confocal microscopy for a better understanding of the secretory process. Samples were prepared according to usual techniques for microscopy. The histochemical tests evidenced the presence of mucilage and proteins in the secretion. Lipids were observed in the cuticle and cuticular extracts, however, neither starch nor phenol was evident. Were observed two mechanisms of secretion: Rupture of cuticle and passage of secretion through the cuticle. With the end of the secretory process, the coléter enters a senescent stage, being characterized by the wrinkling of the cuticle and color change.