Meristematic activity of the Endodermis and the Pericycle in the primary thickening in monocotyledons: considerations on the "PTM"

Abstract

This paper proposes a new interpretation for primary thickening in monocotyledons. The anatomy of the vegetative organs of the following species was examined: Cephalostemon riedelianus (Rapataceae), Cyperus papyrus (Cyperaceae), Lagenocarpus rigidus, L. junciformis (Cyperaceae), Echinodorus paniculatus (Alismataceae) and Zingiber officinale (Zingiberaceae). The endodermis with meristematic activity was observed in the root of all the species, in the stem of Cyperus, Cephalostemum and Lagenocarpus rigidus, and in the leaf trace of Cyperus and leaf of Echinodorus. Considering the continuity of tissues through the root, stem and leaf, the authors conclude that in the stem the pericycle remains active throughout the life of the plant as the generator of the vascular tissue. The "Primary Thickening Meristem" is in fact the pericycle plus the endodermis and its derivatives (or only the pericycle). Close to the stem apex, the assemblage of seems to be a unique meristem, giving rise to the inner cortex and vascular tissues.

Axillary bud and pericycle involved in the thickening process of the rhizophore nodes in Smilax species

“…The data presented here support the proposal by Menezes et al (2012) that, in monocotyledons, the pericycle itself is involved in the thickening process with the formation of new vascular bundles and parenchyma. Moreover, the continuity of the endodermis of the rhizophores and adventitious roots, observed on their emission sites, corroborates the statements that the endodermis is a continuous tissue present in roots and stems (Menezes et al, 2005). The involvement of the axillary bud in the nodal thickening process and consequent rooting in the studied species had already been observed in stem cuttings of S. fluminensis (Soares et al, 2011).…”

“…The primary thickening in monocotyledons has been discussed under a different approach by Menezes et al (2005Menezes et al ( , 2012. According to them, in some species, such as Zingiber officinale (Zingiberaceae), the observation of Casparian bands in the endodermis allowed researchers to verify that the pericycle is involved in the tuberisation process of the rhizome.…”

Anatomia do escapo e rizoma de espécies brasileiras de Bulbostylis Kunth (Cyperaceae)

“…Conforme já demonstrado por Menezes et al (2005) em Cyperus papyrus L., e em outras monocotiledôneas, no rizoma de Bulbostylis o estelo é do tipo atactostelo (figuras 1-3). Nesse tipo de estelo, internamente à endoderme encontra-se o periciclo, camada geradora de tecidos vasculares quando só ocorre espessamento primário, conforme demonstrado por Van Tieghem (1898), Ogura (1972) e outros pesquisadores do século XIX e confirmado por Menezes et al (2005). Internamente ao periciclo, observam-se numerosos feixes vasculares, constituídos de xilema e floema primários (figuras 2-3).…”

Aspectos fisiológicos, anatômicos e ultra-estruturais do rizoma de Costus arabicus L. (Costaceae) sob condições de déficit hídrico

“…Em Canna indica L. (Cannaceae), a presença da endoderme no rizoma foi inicialmente observada por Van Fleet (1942); e um estudo com Canna edulis Kerr-Gawler constatou que no rizoma dessa espécie, a endoderme com estrias de Caspary delimita o córtex do cilindro vascular (Alonso & Moraes-Dallaqua 2004), característica também observada em Costus arabicus. Menezes et al (2005) também constataram a presença da endoderme no rizoma de Zingiber offi cinale Roscoe (Zingiberaceae).…”

“…Segundo Menezes et al (2005), o periciclo do caule de Zingiber offi cinale é, sem dúvida, a camada de geração de tecidos vasculares. Diferentemente de Heliconia angusta, Heliconia velloziana (Simão & Scatena 2001),e Costus pilgeri (Lorca et al 1995), que apresentam periciclo unisseriado, e Canna edulis que possui periciclo plurisseriado (Alonso & Moraes-Dallaqua 2004), Costus arabicus apresenta periciclo bisseriado, sendo a camada responsável pela formação dos feixes vasculares.…”