The development of anastomosed laticifers in the stem apical meristem and vascular cambium of Hancornia speciosa (Apocynaceae) is related to climatic seasonality

Key message In Hancornia speciosa , the latex is synthesized in the cytosol of the ground meristem cells and in plastids of the fusiform derivatives of secondary phloem. Laticifer development is related to climatic seasonality. Hancornia speciosa is a latescent species that grows in the Brazilian Cerrado (neotropical savanna) and shows significant potential for rubber production and the extraction of bioactive compounds from its latex. We examined the development of laticifers in its stem apex and secondary phloem in relation to climate seasonality. Morphometric evaluations of elongating branches and micromorphometric evaluations of the cambial zone were carried out monthly for 1 year, with structural and ultrastructural analyses of the stem apex and secondary phloem. Laticifer development in both the stem apex and secondary phloem is related to increasing day length and maximum temperature and humidity. Laticifers are formed by anastomosis of the transverse and longitudinal walls of the ground meristem cells of the stem apex, and the fusiform derivatives of secondary phloem in the cambial zone. The process of latex secretion involves the synthesis of terpenic droplets in the cytoplasm of the ground meristem cells of the stem apex and in the plastids of the fusiform derivatives of secondary phloem. Latex is an emulsion formed by the cytosol terpenic droplets engulfed by vacuoles contaning mucilages and proteins secreted by dictyosomes and rough endoplasmic reticulum, and alkaloids secreted by the phloem cells. This work expands our knowledge concerning the development of laticifers in Apocynaceae and contributes to our better understanding of the influence of environmental factors on latex secretion.