New insights into laticifers in Mimosa caesalpiniifolia Benth. (Fabaceae): anatomy, ultrastructure, and development, emphasizing the presence of callose

Laticifers are specialized structures found in diverse plant families and are regarded as important components of plant defense systems. In Fabaceae, however, laticifers are relatively uncommon and have been reported in only a few genera, including Mimosa. Despite this, little is known about the ultrastructural features of laticifer protoplasts and cell walls in this group, as well as their distribution throughout the plant body. This study investigated the distribution, anatomy, and ultrastructure of laticifers in Mimosa caesalpiniifolia Benth. (Fabaceae: Caesalpinioideae) from a developmental perspective, encompassing the embryo, seedling, and adult stages. Articulated nonanastomosing laticifers were found associated with both primary and secondary phloem. Total lipids, acidic polysaccharides, and terpenes were detected within the laticifer protoplasts. Primordial laticifer cells displayed thick pectocellulosic walls containing plasmodesmata, dense cytoplasm and abundant organelles. Young laticifers exhibited digitiform extensions toward neighboring cells, while in maturing laticifers, the terminal walls of aligned cells underwent dissolution. Mature laticifers showed an additional discontinuous internal parietal layer of uniform appearance, composed of callose. To the best of our knowledge, this study provides the first report of callose in laticifers of a legume species. The potential protective role of callose as a self-cytotoxic barrier and as a defense mechanism against natural enemies in the laticifer system is hypothesized. This study fills an important gap in the knowledge of laticifer origin and typology in Fabaceae and provides valuable insights to support taxonomic, ecological, and sustainable-use studies of this multipurpose forest species native to the Brazilian semi-arid region. Main Conclusion. Articulated, nonanastomosing laticifers are present throughout the development of Mimosa caesalpiniifolia, occurring in mature embryos,seedlings, and adult plants. A discontinuous parietal layer composed of callose internally lines the laticifer cells.