Anais da Academia Brasileira de Ciências (2005) 77(2): 259-274 (Annals of the Brazilian Academy of Sciences) ISSN 0001-3765 www.scielo.br/aabc Meristematic activity of the Endodermis and the Pericycle in the primary thickening in monocotyledons. Considerations on the “PTM” NANUZA L. DE MENEZES1, DELMIRA C. SILVA2, ROSANI C.O. ARRUDA3, GLADYS F. MELO-DE-PINNA1, VANESSA A. CARDOSO1, NEUZA M. CASTRO4, VERA L. SCATENA5 and EDNA SCREMIN-DIAS6 1Universidade de São Paulo, Instituto de Biociências Rua do Matão 277, Travessa 14, Cx. Postal 11461, Cidade Universitária, 05422-970 São Paulo, SP, Brasil 2Universidade Estadual de Santa Cruz, Departamento de Biologia Campus Soane Nazaré de Andrade, Km16, Rodovia Ilhéus-Itabuna, 45662-000 Ilhéus, BA, Brasil 3Universidade Federal do Estado do Rio de Janeiro, Centro de Ciências Biológicas e da Saúde Av. Pasteur 458, 22290-240 Rio de Janeiro, RJ, Brasil 4Universidade Federal de Uberlândia, Instituto de Biologia Campus Umuarama, Bloco 2D, Sala 28, 3840-902 Uberlândia, MG, Brasil 5Universidade Estadual de São Paulo, Instituto de Biociências de Rio Claro, Departamento de Botânica Av. 24A, 1515, Bela Vista, 13506-900 Rio Claro, SP, Brasil 6Universidade Federal de Mato Grosso do Sul, Centro de Ciências Biológicas e da Saúde(CCBS, DBI) Laboratório de Botânica, Cx. Postal 649, 74070-900 Campo Grande, MS, Brasil Manuscript received on February 11, 2005; accepted for publication on February 16, 2005; contributed by Nanuza L. de Menezes* 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 (Alis- mataceae) 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. Key words: Cephalostemon, Cyperus, Echinodorus, Lagenocarpus, Zingiber, meristematic endodermis, pericycle, primary thickening. INTRODUCTION Since the 19th Century, researchers have presented *Member Academia Brasileira de Ciências Correspondence to: Nanuza L. de Menezes proposals in an attempt to understand the tissues that E-mail: [email protected] form the primary body of a monocotyledon stem, An Acad Bras Cienc (2005) 77 (2) 260 NANUZA L. DE MENEZES ET AL. in particular, the limit zone between the cortex and histochemical system, and all these cells develop or the vascular cylinder. According to Mangin (1882), are induced to develop Casparian strips. Van Fleet this zone has been given different denomina- (1961) admits, as a sine qua non condition, the en- tions, such as the “pericambium”, “perimeristem”, dodermis as the inner cortex layer in the root, stem “properimeristem”, “generating zone”, “couche and petiole; and the inner layer of the mesophyll. dyctiogène”, and “thickening ring”. However, there The author draws attention to the fact that many au- has general agreement that this zone is made up of thors denominate the endodermis as “endodermoid adventitious roots. layer” when it presents Casparian strips in the stem More recently, authors attempting to un- and leaves, a term with which he does not agree. derstand this region have admitted the presence of a Another aspect which has been somewhat ne- primary thickening meristem (PTM), which is re- glected, is the radial disposition of the cortex cells sponsible for the primary thickening of the stem of the roots of mono and dicotyledons, a radiation in virtually all monocotyledons, as Rudall (1991) which originates in the cells of the endodermis. Ac- clearly demonstrates in her revision work on the cording to Mangin (1882), the root cortex of mono- PTM. For the same author (Rudall 1991) and oth- cotyledons consists of two regions: the external re- ers (especially Cheadle 1937, DeMason 1979a, b, gion, with disorganized parenchymatous cells, and 1980, 1983, Stevenson and Fisher 1980, DeMason the internal region, with cells organized in radial and Wilson 1985, Gifford and Bayer 1995), the rows. Of those who attempted to interpret these function of promoting the formation of adventitious radial rows of cells, the pioneers were Williams roots has also been attributed to the PTM. (1947), Hurst (1956 apud Van Fleet 1961) and Van Also according to Rudall (1991), some authors Fleet (1961). admit that the PTM corresponds to the pericyclic Williams (1947), while studying the apical region of the stem. Tomlinson and Zimmermann meristem, as well as the primary tissues in 74 species (1969, p. 174) states, literally, that “The problem of monocotyledons and 105 species of dicotyledons, was to decide whether there was a region in the demonstrated the presence of a layer of cells, which monocotyledonous stem, to which the term “peri- he denominated the plerome, a layer which would cycle” could be given. This is an entirely artificial later differentiate into the endodermis. Cortical cells concept, since in most monocotyledonous stems, the in all the roots investigated were produced by the cortex and central cylinder each end where the other rapid division of this layer of cells, and the arrange- begins”. ment of the cortical cells in relationship to the en- Another theme which has generated much dodermal layer, suggests the meristematic nature of polemic debate is the presence of the endodermis this layer, functioning as a true cambium. Following in the stem and leaves. In his extraordinary revi- the work of Williams (1947), Hurst (1956 apud Van sion work, Van Fleet (1961) demonstrates, giving a Fleet 1961) describes the same type of division in wealth of data and details, the presence of the en- Smilax as the results of a pro-endodermis, and hence dodermis in these organs. According to this author, Van Fleet (1961) refer to the endodermis as meris- although in the root (and underground stems) it can tematic. Heimsch (1951), studying the development be characterized by the presence of the Casparian of vascular tissue in the roots of barley, mentions strips, suberized walls or unilaterial deposits of cel- the works of Williams (1947), as being in agree- lulose in the aerial stems and leaves, it may or may ment with his own. However, in the roots of Pisum not present Casparian strips and other characteris- sativum, this same layer was referred to as a pro- tics, denominated “starch sheath”, “bundle sheath”, endodermal layer (Popham 1955), and again, more “border parenchyma” and “mestome sheath”. How- recently, in Trifolium (Mueller 1991), Hydrocharis ever, these varied types of cells produce the same morsus-ranae (Seago et al. 1999), and in Typha An Acad Bras Cienc (2005) 77 (2) PRIMARY THICKENING IN MONOCOTYLEDONS 261 glaucai (Seago and Scholey 1999). the vouchers were deposited in the departmental Urano and Menezes (1996), with Cephaloste- herbarium (SPF). mon riedelianus, and Conceição and Menezes Rhizomes of Cephalostemon riedelianus Ko- (1996), with Nymphoides indica, refer to these ra- ern (Rapateaceae), N. Menezes 1347 b (SPF), and of diate layers as the result of “mother cells of the en- Lagenocarpus rigidus (Kunth.) Nees (Cyperaceae), dodermis”. On the other hand, Melo-de-Pinna and Vitta 690 (UEC), L. junciformis (Kunth) O. Kunth, Menezes (2003) refer to these layers as being the re- Vitta 540 (UEC) were collected at Serra do Cipó sults of meristematic activity of the endodermis, fol- (MG). Leaves of Echinodorus paniculatus Micheli lowingWilliams (1947) andVan Fleet (1961). Chea- (Alismataceae) were collected in Mato Grosso do dle (1937), observes the presence of radiate growth Sul, E. Scremin-Dias s/n (SPF 136.463). in the cortex of the root in Dracaena goldieana, The rhizomes of Cephalostemon and Lageno- external to the intact endodermis, and names this ra- carpus, as well as the leaves of Echinodorus, were diate region a “secondary cambial zone”. Guillaud fixed in FAA (Johansen 1940); following dehydra- (1878), referring to the same region also mentions a tion in ethanol series, the material was conserved “meristem external to the endodermis”, in reference in ethanol 70%. After inclusion in paraffin, histo- to the same region of radiate cortical cells. logical sections varying from 10 to 15 µm in thick- According to Cheadle (1937), there is no clear ness were prepared according to standard techniques differentiation of tissues on the cauline apex, and (Sass 1951, Johansen 1940). Later, the sections it therefore seems impossible to detect which layer were stained with astra blue and safranin (Bukatsch originates what he denominates as a “thickening 1972), concomitant with a double staining of crys- ring”. This could be the pericycle, which is gener- tal violet and Orange G (Purvis et al. 1964). The ally accepted as being outermost layer of the stele, slides were secured by sealing the cover slips with or possibly the endodermis, the innermost layer of Canadian balsam. the cortex. The rhizomes of Cyperus and Zingiber were The aims of this paper are to demonstrate: hand cut using a razor blade, and the cuts, after stain- ing with astra blue and safranin (Kraus et al. 1998), (1) the continuity of tissues between the root, stem were mounted in 33% glycerin. For suberin, Sudan and leaf in monocotyledons; IV was used. (2) the pericycle as a generating layer of vascular tissues; RESULTS (3) the endodermis as having a meristematic func- The cortex in the root of Cyperus papyrus (Fig. 1-3) tion in the root, stem and leaf, combining to was found to be composed mostly of radiate rows form part of the stem and root cortex and part of cells originating from the endodermis.