Primary and secondary thickening in the stem of Cordyline fruticosa (Agavaceae)

The growth in thickness of monocotyledon stems can be either primary, or primary and secondary. Most of the authors consider this thickening as a result of the PTM (Primary Thickening Meristem) and the STM (Secondary Thickening Meristem) activity. There are differences in the interpretation of which meristem would be responsible for primary thickening. In Cordyline fruticosa the procambium forms two types of vascular bundles: collateral leaf traces (with proto and metaxylem and proto and metaphloem), and concentric cauline bundles (with metaxylem and metaphloem). The procambium also forms the pericycle, the outermost layer of the vascular cylinder consisting of smaller and less intensely colored cells that are divided irregularly to form new vascular bundles. The pericycle continues the procambial activity, but only produces concentric cauline bundles. It was possible to conclude that the pericycle is responsible for the primary thickening of this species. Further away from the apex, the pericyclic cells undergo periclinal divisions and produce a meristematic layer: the secondary thickening meristem. The analysis of serial sections shows that the pericycle and STM are continuous in this species, and it is clear that the STM originates in the pericycle.The endodermis is acknowledged only as the innermost layer of the cortex.O crescimento em espessura do caule de monocotiledônea pode ser primário, ou primário e secundário. A maioria dos autores consideram o espessamento resultante do MEP (Meristema de Espessamento Primário) e do MES (Meristema de Espessamento Secundário). Há divergências de qual seria o meristema responsável pelo espessamento primário. Em Cordyline fruticosa o procâmbio forma feixes vasculares de dois tipos: traços foliares colaterais (com proto e metaxilema e proto e metafloema), e feixes caulinares concêntricos (com metaxilema e metafloema). O procâmbio também forma o periciclo, a camada mais externa do cilindro vascular, constituída por células menores e menos coradas que se dividem irregularmente, formando novos feixes vasculares. O periciclo dá continuidade à atividade procambial, originando somente feixes concêntricos. Concluiu-se ser o periciclo responsável pelo espessamento primário desta espécie. Mais distante do ápice as células pericíclicas passam a sofrer divisões periclinais originando o Meristema de Espessamento Secundário. A análise dos cortes seriados mostra que o periciclo e o MES são contínuos nesta espécie, ficando claro que o periciclo origina oMES. A endoderme é reconhecida, apenas, como a camada mais interna do córtex.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Rhizophores in Rhizophora mangle L: an alternative interpretation of so-called ''aerial roots''

Rhizophora mangle L., one of the most common mangrove species, has an aerial structure system that gives it stability in permanently swampy soils. In fact, these structures, known as "aerial roots" or "stilt roots", have proven to be peculiar branches with positive geotropism, which form a large number of roots when in contact with swampy soils. These organs have a sympodial branching system, wide pith, slightly thickened cortex, collateral vascular bundles, polyarch stele and endarch protoxylem, as in the stem, and a periderm produced by a phellogen at the apex similar to a root cap. They also have the same type of trichosclereid that occurs in the stem, with negative geotropism, unlike true Rhizophora roots, which do not form trichosclereids at all. On the other hand, these branches do not form leaves and in this respect they are similar to roots. These peculiar branches are rhizophores or special root-bearing branches, analogous to those found in Lepidodendrales and other Carboniferous tree ferns that grew in swampy soils

A new interpretation on vascular architecture of the cauline system in Commelinaceae (Commelinales).

The vascular system of monocotyledons, including Commelinaceae, has been studied since the 19th century, but to date, the proposed vascular architecture models consist of schematic representations partially based on the authors' interpretation. One of the greatest difficulties in studying these systems is the large number of vascular bundles and the complexity of their connections, especially in the monocotyledons which have a nodal vascular plexus. In this study, shoot apex samples of 14 species of Commelinaceae were submitted to three-dimensional analyses (confocal microscopy, X-ray microtomography, graphic vectorization, and whole-mount diaphanization), as well as conventional techniques in plant anatomy. Based on the results, a previously unreported category of bundles is described in Commelinaceae for the first time, as well as the fact that peripheral bundles are not interrupted or end blindly in the periphery of the pith, as previously thought. With this new interpretation of the vascular architecture, three patterns of nodal vascular plexus are proposed: 1) in the first pattern the internal nodal vascular plexus (IVP) forms a continuous cylinder and does not connect to the external nodal vascular plexus (EVP); 2) the IVP forms a cylinder divided into two columns and does not connect to the EVP and 3) the IVP forms a cylinder connected to the EVP. The first description of central bundles in the Commelinaceae might suggests their existence in closely related groups, such as the remaining four families of Commelinales (i.e., Haemodoraceae, Hanguanaceae, Philydraceae, and Pontederiaceae), and even in other distantly related groups of monocotyledons

Morfoanatomia do sistema subterrâneo de Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson (Asteraceae)

Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson (Asteraceae), conhecida como yacon, é uma espécie herbácea de clima tropical de altitude, tendo sido introduzida em diversos países, incluindo o Brasil, devido ao seu potencial alimentício, forrageiro e, principalmente, como substrato para a produção de inulina. Embora aspectos agronômicos e bioquímicos desta planta sejam relativamente conhecidos, pouco se sabe a respeito da morfologia e natureza do sistema subterrâneo, principal fonte de inulina. Verificou-se que o sistema subterrâneo tem natureza mista, sendo constituído por rizóforos e raízes delgadas e tuberosas, ambas adventícias. Canais secretores de substâncias lipídicas estão presentes nos rizóforos e raízes; nestas, os canais originam-se nas camadas corticais internas derivadas da endoderme meristemática.Smallanthus sonchifolius (Poepp. & Endl.) H. Robinson (Asteraceae), known as yacon is a high-altitude tropical herbaceous species. It was introduced into several countries, including Brazil, because of its nutritional potential, high yield but mainly as a source of inulin. Although its agronomy and biochemistry are relatively well established, little is known about the morphology and nature of its underground system, the main inulin source. The underground system is heterogeneous in nature, consisting of rhizophores, and adventitious thin and tuberous roots. The rhizophores and roots present secretory ducts of lipid in the inner cortical layers, which is derived from the meristematic endoderm.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq