Mucilage and phenolic-secreting cells in sensitive plants (Mimosa, Leguminosae): a comparative study across different plant organs

Mucilage cells are secretory structures associated with energy reserve and osmotic regulation, acting as a drought resistance mechanism. They are commonly found in legume species and can also contain phenolic compounds. Since they were previously identified in the sepals of one Mimosa species, the objective of the present study was to investigate the occurrence and location of mucilage and phenolic-secreting cells in the floral and leaf organs of species of this genus. We compare vegetative and reproductive organs, providing a detailed understanding of the distribution of these secretory structures throughout the plant body and proposing putative functions for them. Samples of foliar and floral organs of 13 species of Brazilian Mimosa were processed for anatomical analysis. Mucilage cells were found in the leaflet blade, petiole, rachis, rachilla, bract, sepal, and petal of all the species studied. In addition, M. caesalpiniifolia and M. sensitiva appeared to have mucilage cells also in the anther and ovary, and M. pudica in the filament and ovary. These cells occur throughout the entire epidermis of the organ or groups of cells, but may also occur in the mesophyll or in the cortical parenchyma. In most organs and species, mucilage cells usually also include phenolic compounds. Considering the close affinity between the production and accumulation of mucilage and phenolics, these two compounds may operate synergistically for plant protection and/or reproduction in Mimosa.