Articulated and non-articulated laticifers: structure, development and evolution

Abstract

Laticifer is a secretory structure, which occurs in several families of vascular plants, from ferns to the most derived groups of angiosperms, and apparently has appeared several times throughout the evolutionary history of terrestrial plants. Although the descriptions refer to latescent families, a minority of these groups have laticifers in all their members. Likewise, the absence of latex descriptions in numerous species does not imply the absence of laticifers. In addition, the abundance of latex may be related to the structure of the laticifer and water availability, among other factors. It is also necessary to point out that misinterpretations have attributed the presence of laticifers to families that, at first, do not have them. All these factors reinforce the need to perform a broad survey and analysis of the groups described as latescent to reassess their real distribution and evolutionary emergence in the vascular plants. This is one of the objectives of the present work that aims to anatomically evaluate the occurrence of laticifers in the 42 families of vascular plants already described as having at least one latescent member. The laticifer type will also be evaluated, based on its ontogeny, to verify if the diversity described for some groups and the conservation of the character in other ones really reflects different evolutionary events. The other main divergence in the study of laticifers is their mode of growth, especially for the non-articulated laticifers, which are described as having apical intrusive growth between adjacent cells. In this way, this work also aims to study the development of laticifers of Asclepias curassavica (articulated) and Euphorbia milii (non-articulated) through ultrastructural and immunocytochemical analyses of its apices, and pectinase activity evaluation that may be involved in its growth mode. The global gene expression will also be performed and analyzed for these two species along with the formation of the laticifers. The expression pattern will be compared to phylogenetically close species through bioinformatics analysis and, using in situ hybridization, will be accompanied by the differentiation of the laticifers in the meristems. In this way, it is expected to identify definitively the mode of differentiation and growth of the two laticifer types. This will be the first time that laticifers will be investigated evolutionarily on a large scale and, with this project, it is expected to solve the main divergences regarding their occurrence, development and evolution in vascular plants. (AU)