Ontogênese do sistema subterrâneo de Pachyrhizus ahipa (Wedd.) Parodi (Fabaceae)

Abstract

-(Ontogeny of the subterranean system of Pachyrhizus ahipa (Wedd.) Parodi (Fabaceae)). A study on the ontogeny of the underground system of P. ahipa was held with the purpose of understanding both its morphology and its process of tuberization. Samples, collected from the hypocotyl region and from the primary root during different phases of plant development, were processed according to usual technic. The underground system of P. ahipa is composed by both a xylopodium and a tuberous root. The xylopodium is a cylindrical lignified region near the soil and gives rises to new sprouts. Immediately below to this part there is a primary tuberous root, which is predominantly fusiform. The root tuberization results from the activity of a typical vascular cambium and from accessory cambium originated from the parenchyma of the secondary xylem, after the first phase of the usual secondary growth. The xylopodium is of a mixed nature, as it arrises from the hypocotyl and from the base of the primary root.Key words -Anatomy, Pachyrhizus, tuberous root, underground system, xylopodium RESUMO -(Ontogênese do sistema subterrâneo de Pachyrhizus ahipa (Wedd.) Parodi (Fabaceae)). Realizou-se o estudo da ontogênese do sistema subterrâneo de P. ahipa com o objetivo de contribuir para o conhecimento da morfologia, bem como do processo de tuberização dos órgãos subterrâneos desta espécie. Amostras das regiões do hipocótilo e da raiz primária foram retiradas em diferentes fases de desenvolvimento da planta e processadas segundo técnica usual. Verificou-se que o sistema subterrâneo de P. ahipa compreende um xilopódio e uma raiz tuberosa. O xilopódio corresponde a uma porção cilíndrica, lenhosa e lignificada, próxima ao solo, da qual surgem novos brotos. Logo abaixo, encontra-se a raiz primária tuberosa, de formato predominantemente fusiforme. O processo de tuberização da raiz resulta da atividade de um câmbio vascular típico, juntamente com câmbios acessórios que surgem a partir da retomada de divisão celular do parênquima do xilema secundário, após a primeira fase do crescimento secundário usual. A ontogênese do xilopódio mostra que este apresenta natureza mista, formando-se a partir do crescimento secundário tanto do hipocótilo quanto da região basal da raiz primária tuberosa.Palavras-chave -Anatomia, Pachyrhizus, raiz tuberosa, sistema subterrâneo, xilopódio IntroduçãoApesar da relevante importância dos sistemas subterrâneos quanto aos aspectos fisiológicos, ecofisiológicos e econômicos, os estudos morfoanatômicos envolvendo estas estruturas ainda são escassos, diante da grande diversidade encontrada nos diferentes ambientes.Verifica-se, no entanto, que é vasta a terminologia utilizada para classificar sistemas subterrâneos, principalmente os que possuem natureza caulinar (Rocha 1995). Porém, apesar da variedade de termos, muitas vezes eles parecem insuficientes para designar o tipo de órgão subterrâneo que se quer descrever. Deste modo, torna-se necessário a realização de estudos com abordagem morfo-anatômica para a caracter...

Comparative root anatomy of papilionoid Legumes

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Anatomy of the underground system in Vernonia grandiflora Less. and V. brevifolia Less. (Asteraceae)

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