The Occurrence of Intrusive Growth Associated with Articulated Laticifers inTabernaemontana catharinensisA.DC., a New Record for Apocynaceae

Abstract

Premise of research. In Apocynaceae, nonarticulated laticifers have been recorded in most species studied. Interpretation of the mode of development of laticifers, whether articulated or nonarticulated, is controversial, possibly because of the rapid changes that occur in the early differentiation stages of the structures. Here, we describe laticifers in the embryo, seedling, and plant of Tabernaemontana catharinensis A.DC. (Apocynaceae), aiming to understand the structure and developmental mechanism of the laticifer system. Methodology. We prepared samples of mature embryos, 20-d-old seedlings, and 80-d-old plants of T. catharinensis according to conventional light microscopy techniques for anatomical and histochemical analysis. Pivotal results. Articulated anastomosing laticifers with intrusive growth, producing proteins, lipids, and terpenes, are present from mature embryos. Alkaloids are present in the laticifer protoplast of the older portions of the stem. Laticifers of the primary system originate from the ground meristem and procambium, and those of the secondary system originate from the vascular cambium toward the secondary phloem. In the embryo, laticifers are found in the ground meristem and procambium but do not occur in the promeristem; the nodal region exhibits lateral projections between laticifers and ground meristem cells. In seedlings and plants, laticifers are immersed in the parenchyma tissue and associated with the primary and secondary phloem of the root and shoot systems. The anatomical evidence suggests the incorporation of meristematic and parenchyma cells within the laticifer system. Conclusions. The laticifer system of T. catharinensis has a complex structure and developmental mechanism involving protoplast fusion, the addition of cells, and intrusive growth. We recorded, for the first time, the occurrence of intrusive growth associated with articulated anastomosing laticifers in a member of Apocynaceae. Our findings highlight the importance of detailed anatomical analysis to properly classify laticifers and to access their origin and development.

Cytological differentiation and cell wall involvement in the growth mechanisms of articulated laticifers in Tabernaemontana catharinensis A.DC. (Apocynaceae)

“…Intrusive growth is commonly associated with nonarticulated laticifers (Mahlberg 1993), while protoplast fusion and the addition of adjacent cells have been linked to articulated laticifers (Milanez 1959(Milanez , 1977Lopes et al 2009). Remarkably, our study (Canaveze and Machado 2016) showed that such growth mechanisms occur simultaneously during the development of articulated laticifers in the same species and have been observed in distinct vegetative developmental stages. Cellular changes associated with the mechanism that drives the incorporation of cells into the laticifer system have been described in mature embryos (Milanez 1959(Milanez , 1977, but no ultrastructural studies of the laticifers' action-inducing mechanism in other vegetative developmental stages have been conducted.…”

“…Actively secreting laticifers occur in the mature embryo of T. catharinensis (Canaveze and Machado 2016); however, the same labeling patterns of wall glycans in surrounding meristematic cells suggest that laticifer walls in the mature embryo are still under development, as laticifer wall features change throughout plant development. Despite the fact that laticifer walls in the embryo shared the same characteristics of an absence of galactans and a presence of low methyl-esterified HGs and arabinans with laticifer walls in the plant shoot apex, which would confer the necessary flexibility and softness required for intrusive growth, the occurrence of numerous plasmodesmata and callose appears to be a limiting factor for intrusive growth.…”

“…A previous anatomical study of Tabernaemontana catharinensis, an Apocynaceae species, revealed that this species has articulated anastomosing laticifers with a complex structure, and a developmental mechanism involving protoplast fusion, the addition of adjacent cells, and intrusive growth, which occur in mature embryos, seedlings, and plants (Canaveze and Machado 2016). Intrusive growth is commonly associated with nonarticulated laticifers (Mahlberg 1993), while protoplast fusion and the addition of adjacent cells have been linked to articulated laticifers (Milanez 1959(Milanez , 1977Lopes et al 2009).…”

Laticifers and Secretory Ducts: Similarities and Differences

“…This way, this type of laticifer would present cell division without the occurrence of cytokinesis, forming a long multinucleated, coenocytic tube [9,[33][34][35][36] ( Figure 1F). Although this type of growth has also been recorded for a few articulated laticifers [35,37], several studies have demonstrated the impossibility of its occurrence due to the absence of a subcellular apparatus capable of constantly producing cell wall at the laticifer tip [38], besides the lack of records of karyokinesis within laticifers in the main families of latescent plants [7,39,40]. Thus, the possible unlimited growth of the laticifer needs to be reviewed, and the record of articulated and non-articulated laticifers in the same genus and even in the same species should be re-evaluated ontogenetically [7,33,35,[39][40][41], since the current data point to the absence of non-articulated laticifers in all the families in which they were described.…”

Laticifers in vascular plants

“…Several papers support the theory of intrusive apical growth in non-articulated laticifers (Snyder 1955, Wilson and Mahlberg 1977, Mahlberg 1993) and in some articulated laticifers (Rudall 1994, Canaveze and Machado 2016, Canaveze et al 2019. According to this theory, laticifers would develop in the intercellular spaces of plant tissues (Mahlberg 1993).…”