The role of the endodermis and pericycle in the formation of primary tissues in Commelinaceae (Monocotyledons) / Estudos em Commelinaceae (Monocotiledôneas): o papel da endoderme e do periciclo na formação do corpo primário

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The aim of this work is to show the meristematic activity of the endodermis in roots of five species of Commelinaceae (Commelina erecta, Floscopa glabrata, Dichorisandra tyrsiflora, Tradescantia spathacea e T. zebrina). In all species was observed the initial endodermis suffered several periclinal divisions, originating the radiate layers of the cortex cells. In addition, these divisions does not stop simultaneously in all initial cells because, when differentiation occurs, cells that had a last division apears beside cells that have not divide yet. The generation of cells by the endodermis can be verified observing its subsequent cells. These subsequent cells are disposed as rows and in a radiate pattern where is possible to observe a progression in cell size, that is, the cells become greater as the distance from the endodermis increases. These rows of cells are derived from the endodermis and are called derivatives of the meristematic endodermis (DME). In the stem, the meristematic activity of pericycle and endodermis is limited to the nodal region. In this region occurs the formation of new adventitious roots, buds and leaf traces. In the internodes the vascular bundles are collateral, the endodermis usually appears as a starch sheath, which may have Caspary strips, and the pericycle is parenchymatous. In the nodal region, there is intensive activity of pericycle (or pericycle region), promoting the formation of vascular bundles with fibers around it, and the peripheral plexus of adventitious roots. Moreover, there was also little activity of endodermis producing only from two to three layers of inner cortex. The endodermis has suberin. In conclusion, the primary thickening is caused by the centripetal activity of pericycle and the centrifugal activity of the endodermis. In specialized literature, reports on anatomy of presence of the endodermis and the pericycle in leaves of vascular plants are few in number. Most authors consider the tissues that involve the leaves bundles as sheath bundle. The aim of this work was to show the sheath bundle is composed by the endodermis and the pericycle, and investigate the continuity of tissues between stem and leaf in Monocotyledons. The results showed that there is a perfect continuity between the tissues of stem and leaf when the leaf trace is observed going in direction to the leaf. In addition, it was observed that the endodermis of stem involve not only the vascular cylinder but also the leaf bundles, that is, the monosteles. The presence of Caspary strip in the endodermis was not observed. It was decided to name the leaf bundle as unity instead of bundle, as proposed for recently researches. In specialized literature, reports on anatomy of miners in host plants are few in number. These agents trigger excavations, or paths, by consumption of plant inner tissues by larvae of several insects. The aim of this work was to investigate leaf miner occurrence in Commelina diffusa and Floscopa glabrata using anatomical techniques. In this case, it was discovered that members of Agromyzidae and Chironomidae families, which are Diptera endophytophagous larvae types, were responsible for the tunnels. Moreover, in Commelina diffusa was found Agromyzidae larvae while in Floscopa glabrata three Chironomidae cephalic exuviae were found. The miners, as shown by anatomical studies, used only parenchymatic tissues of mesophyll for their feeding, causing the formation of linear miners. In addition, the epidermis and the middle-sized vessel bundles, in both species, were kept intact, showing no structural modification, like neoformation of tissues.

ASSUNTO(S)

pericycle commelinaceae endodermis periciclo endoderme commelinaceae

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