Anatomia de raízes e caules de Bignonieae: síndrome lianescente e xilema secundário

Abstract

Lianas have stems with a very specialized anatomical architecture, with attributes that allows efficient conductivity and flexibility. Among the suite of features, collectively named "lianescent vascular syndrome", we can quote the presence of cambial variants (which are unusual patterns of secondary growth), vessel dimorphism (presence of wide and narrow vessel co-occurring, sometimes associated), fewer fibres or thin-walled fibres, tall and large rays, and abundant parenchyma (occasionally non-lignified, both on axial and radial axis) when compared with related self-supporting species. Most of lianas in Bignoniaceae are comprised in the tribe Bignonieae, a large and morphologically diverse neotropical clade, possessing the cambial variant "furrowed xylem" as synapomorphy. The stem anatomy of Bignonieae lianas is well known, but data about root anatomy are scarce. It is known that cambial variants occur in roots of some Bignonieae, but there is no information about other features of the secondary structure. Thus, the aim of this study is to elucidate some questions, dividing the analysis in two parts. In the first chapter, we intent to verify the presence of cambial variants in roots and stems, and possible attributes related to vascular lianescent syndrome in roots. In the second chapter we analyze the anatomical settings of secondary xylem in roots and stems, in order to verify possible differences between them. The key results obtained are here synthetized: (i) roots have cambial variants similar to stems, but the phloem wedges form interspersed and in same number as the protoxylem poles; (ii) in Amphilophium the included phloem wedges, a characteristic of the genus, are also included in secondary phloem, besides the xylem; (iii) presence of vascular neoformations in Amphilophium, formed by cells in nonconducting portion of the phloem, increasing the conductive area; (iv) presence of vessel dimorphism and tall and large rays, plus cambial variant, characteristic of vascular lianescent syndrome in the roots of the analyzed species, similar to stems; (v) the qualitative features of the xylem are similar between roots and stems, as are statistically similar the quantitative features. We believe that more studies are necessary in the genetic and hormonal field, aiming to understand why the lianescent syndrome occurs in organs subjected to different growth conditions.

The role of ontogeny in wood diversity and evolution

“…The shared origins of all cambial initials thus render all cell types in the xylem serially homologous (sensu Rutishauser and Moline, 2005). The homology in cell types is evident by the abundance of intermediate forms between each of the categories; for example, starch storing fusiform elements intermediate between axial parenchyma and fibers in Paullinia (Sapindaceae) (Chery et al, 2020a; Figure 3A) or xylem elements which are partially axial parenchyma and partially vessels (Figure 3B), cells named perforated axial parenchyma by Victorio (2016). The complex development of the xylem as a whole, and the unique ontogeny of each cell type, has the capacity to generate an enormous array of diversity.…”