Desenvolvimento pós-seminal de espécies de Poaceae (Poales)

Abstract

RESUMO -(Desenvolvimento pós-seminal de espécies de Poaceae (Poales)). O presente estudo objetivou verificar a existência de um padrão do desenvolvimento pós-seminal em Poaceae. Para tanto, foram estudadas as seguintes espécies: Olyra humilis Nees (Bambusoideae); Axonopus aureus P. Beauv. e Paspalum polyphyllum Nees ex Trin. (Panicoideae); Chloris elata Nees e Eragrostis solida Desv. (Chloridoideae). Procurou-se também comparar as estruturas da plântula de Poaceae com as demais monocotiledôneas. As espécies estudadas são plantas perenes, rizomatosas, cespitosas e apresentam cariopses de tamanhos diferentes. Apresentam sementes albuminosas; embrião lateral, diferenciado, com raiz endógena (adventícia); cotilédone dividido em hiperfilo (escutelo), bainha reduzida e hipofilo (coleóptilo); coleorriza (raiz primária reduzida) e mesocótilo (eixo localizado entre o escutelo e coleóptilo). A presença de epiblasto (folha embrionária) foi observada em Olyra humilis, Chloris elata e Eragrostis solida. O desenvolvimento pós-seminal é semelhante nas espécies estudadas e forma um padrão em Poaceae. Primeiramente, observa-se a emissão da coleorriza, que cresce no sentido geotrópico positivo, seguida do coleóptilo e plúmula que crescem em sentido contrário, a partir do desenvolvimento do mesocótilo. As primeiras folhas são semelhantes às folhas definitivas (metafilos) das espécies, exceto em Olyra humilis, que são modificadas em catafilos e podem ser interpretadas como caráter basal em Bambusoideae. Raiz primária reduzida (coleorriza) e hipofilo modificado em coleóptilo são considerados caracteres derivados em Poaceae, quando comparados com as demais monocotiledôneas.Palavras-chave: anatomia, Gramineae, morfologia, plântula, semente ABSTRACT -(Post-seminal development of Poaceae species (Poales)). This work has aimed to verify the existence of a pattern of the post-seminal development in Poaceae. Thus, Olyra humilis Nees (Bambusoideae); Axonopus aureus P. Beauv. e Paspalum polyphyllum Nees ex Trin. (Panicoideae); Chloris elata Nees e Eragrostis solida Desv. (Chloridoideae) have been studied. Besides, it was compared the structures of Poaceae seedlings with those of other monocotyledons. All are perennial, rhizomatous, and cespitous species whose caryopses differ in size. They all present albuminous seeds, lateral and differentiated embryos, with endogenous embryonic (adventitious) root, cotyledons divided into hyperphyll (scutellum), reduced sheath and hypophyll (coleoptile); coleorhiza (reduced primary root); and mesocotyl (axis between the scutellum and the coleoptile). The presence of epiblasts (embryonic leaves) was noticed in Olyra humilis, Chloris elata and Eragrostis solida. Since the post-seminal developmental of all the studied species is similar, it represents a pattern in Poeaceae. The coleorhiza, which shows positive geotropism, grows first, followed by the coleoptile and the plumule, in the opposite direction, which form from the mesocotyl development. In all species, the first leaves are similar to the definitive ...

Morphology and anatomy of the diaspores and seedling of Paspalum (Poaceae, Poales)

“…The anatomical structures of the Paspalum seedlings studied in this work correspond to those already described for others representatives of the genus (Hoshikawa 1969, Nakamura andScatena 2009). Characters, such as a well-developed sheath and blade of the first leaf and the absence of an epiblast, are considered derivative in Poaceae and corroborate the intermediate position of the genus in the family (GPWG 2001).…”

“…subaequiglume caryopses was correlated with other Poaceae and can be considered an important character of the infrageneric level (Filgueiras 1986). The studied species present albuminous seeds, an embryo laterally attached to the endosperm, the presence of a coleoptile, mesocotyl and a reduction of the primary root in the seedling, as previously described for other Poaceae (Martin 1946, GPWG 2001, Tillich 2007, Nakamura and Scatena 2009. The "panicoid"-type vascularization in the embryo was verified in other representatives of the tribe Paniceae and, therefore, has taxonomic importance in Poaceae (Reeder 1957).…”

“…In the studied species of Paspalum, the primary root is reduced, remaining as a vestige in the coleorhiza form, as reported also for other Poaceae (Cocucci and Astegiano 1978, Tillich 2007, Nakamura and Scatena 2009. In monocots, the reduction of the primary root has occurred throughout evolution, and its absence is a derivative character (Boyd 1931, Tillich 2007.…”

“…The post-seminal development is similar among the studied Paspalum species, independent of their growth form when adults, and it constitutes a pattern for the group as observed in other Poaceae (Tillich 2007, Nakamura andScatena 2009). Regarding the rhizomatous growth form, the stoloniferous, erect caespitose and decumbent caespitose present similar initial seedling stages, with the rhizome originating from the mesocotyl.…”

“…The inflorescence types and growth forms of Paspalum are related to the group's taxonomy Weberling 1995, Rua andGrottola 1997), and the morphology and anatomy of the seed and postseminal development indicate the homogeneity in the family (Hoshikawa 1969, Morita et al 1997, Nakamura and Scatena 2009.…”