Foliar morpho-anatomy of Araujia odorata (Apocynaceae - Asclepiadoideae) in an altitudinal gradient. Histochemistry of laticifers

Araujia odorata is a sub-shrub native from Argentina, Brazil, Paraguay and Uruguay, whose latex, roots and leaves are used in traditional medicine. The objective of this work is to study the foliar morpho-anatomy of six populations in an altitudinal gradient (359-2155 m.a.s.l.) of Northwestern Argentine and to determine the nature of the compounds present in the laticiferous of the stems and fruits using conventional techniques for plant anatomy. The populations under study did not show significant morpho-anatomical differences. They presented simple leaves, pinnated brochydodromous venation, amphiestomatic isolateral lamina, brachy, anomo and amphicyclocytic stomata, eglandular trichomes, midvein with bicolateral vascular bundle and non-articulated laticifers continuous in the petiole, stem and fruits. Differences in the quantified foliar parameters are observed, however, only the density of trichomes, stomata and the thickness of the cuticle are positively correlated with the altitudinal gradient, indicating phenotypic plasticity. Histochemical analysis of laticifers and other stem idioblasts of A. odorata was performed for the first time.

Laticifer systems in Mandevilla illustris and M. velutina apocynaceae

Two <em>Apocynaceae</em> species from savanna (Cerrado) area of Sao Paulo State, Brazil were studied. In both Mandevilla species examined, the laticifer systems are of non-articulated branched type, characteristic of the family. In vegetative organs reported was the occurrence of a primary laticifer system of which the cells were differentiated in the embryo. However, additional laticifer cells were always produced during the growth of the shoot apex. A secondary laticiferous system produced by the cells of vascular cambium was identified in the tuberous root and in the stem. A proposed discussion on this apparently unique record in <em>Apocynaceae</em> was arisen to evaluate the main distinction between articulated and non-articulated laticifers.

Significance of follicle anatomy of Apocynaceae

The pericarp structure of <i>Aganosma</i>, <i>Alstonia</i>, <i>Catharanthus</i> sp., <i>Holarrhena</i>, <i>Ichnocarpus</i>, <i>Parsonsia</i>, <i>Strophanthus</i>, <i>Vallaris</i> and <i>Wrightia</i> sp. distinguished into epicarp, mesocarp and endocarp has been used to put forward their taxonomic and phylogenetic importance. Epicarp is single layered in <i>Catharanthus</i> sp., <i>Ichnocarpus</i>, <i>Parsonsia</i> and <i>Vinca</i>, while in the rest of the genera it is multilayered. Mesocarp is parenchymatous which embeds vasculature and non-articulated laticifers. Endocarp is multilayered and thick walled. Dehiscence of the follicle is marginicidal. A comparison table of follicular features of <i>Apocynaceae</i>, <i>Asclepiadaceae</i> and <i>Periplocaceae</i> is furnished and their features are discussed. A taxonomic key based on follicular fruit characteristic to indentify the genera and species is appended.

Articulated laticifers in the vegetative organs of Mandevilla atroviolacea (Apocynaceae, Apocynoideae)

The occurrence of nonarticulated laticifers has been recorded in the literature for Apocynaceae, but little information is available on their structure and the chemical compounds in their latex. The objective of this study was to describe, anatomically and histochemically, the laticifers and latex found in the roots, stems, and leaves of Mandevilla atroviolacea (Stadelm) Woodson, a genus in the Apocynaceae. Laticifer anatomy was examined by light microscopy, and the chemical nature of the exuded latex was studied using cytochemistry. Articulated laticifers were present in M. atroviolacea. The lactiferous system in stems and leaves originated from both procambium and ground meristem, and it was determined to be functional, as indicated by changes in the cytoplasm immediately subsequent to its formation. However, in tuberous roots, laticifers originated from the vascular cambium, phellogen, and parenchymatous cortical cells. The primary wall of laticifers consists of pectins and cellulose and is thicker than that of adjacent cells. The laticifer secretion contained an emulsion of lipophilic substances rich in neutral lipids, resin oils, and possibly rubber. The presence of articulated laticifers is reported for the first time for Apocynoideae, contributing to the knowledge and understanding of these structures in the family Apocynaceae.