The structure of the endoparasite angiosperm Pilostyles ulei (Apodanthaceae): interface and impact on Mimosa ssp xylem / A estrutura da angiosperma endoparasita Pilostyles ulei (Apodanthaceae): interface e impacto no lenho de Mimosa spp

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Pilostyles (Apodanthaceae) are endoparasitic angiosperms of Fabaceae stems and one of the most remarkable situations of body reduction. This study focuses the vegetative body of P. ulei. From an external view, there are only tiny flowers which break out the host periderm. Internally, they are connected to masses of vegetative body. These masses, formed by parenchyma (which have no storage function), occupy especially the phloem area of the Mimosoidea hosts. From them, groups of twisted tracheary elements surrounded by parenchyma cells - called sinkers - run into the host secondary xylem. Tracheary elements were interpreted as tracheids, with helicoidal to scalariform thickening. Due to their disorganised and twisted features, parasite tracheids could be considered not perfectly connected to each other and from the rest of the body. The contact zone shows wide morphological plasticity. Here is described, by the first time, the wide range of sinker positioning in the host-parasite interface. Usually, sinker parenchyma contacts host parenchyma. Successive images show that only a few parasite tracheids successfully reach the host vessel. There are unique associations between parasite tracheids and host vessels which lead to other forms of contact. Sinker can rotate and be laterally positioned to the host vessel. Moreover, host vessels elements can head for sinkers, in ways of a strong attraction never documented.¶ Pilostyles (Apodanthaceae) are endoparasitic angiosperms of Fabaceae stems. The vegetative body, the endophyte, consists of masses of parenchyma cells and sinkers. Sinker development causes gaps in host tissues. Parasite protoplast parenchyma, not associated with sinkers, can occupy host cell lumina. The entrance starts in host ray cells and spread to secondary xylem cells. Parasite and host cells do not form secondary plamodesmata. However, host wall degeneration can occur beside a parasite cell. Host cells also can be completely deteriorated or promote phenol compounds accumulation. Pilostyles (Apodanthaceae) are endoparasites of Fabaceae stems. The body structure consists of masses of parenchyma cells in the host phloem and groups of twisted tracheary elements surrounded by parenchyma cells - called sinkers - running into the host secondary xylem. This is the first study focusing the impact of the holoparasite Pilostyles parasitism on the host secondary xylem stem. From populations of Mimosa foliolosa, M. maguirei and M. setosa were obtained "healthy" and parasited stems by P. ulei. Measurements of vessel element lenght, fiber lenght, vessel diameter and vessel frequency were made on digital imaging. Height, basal diameter and basal circumference of stem in M. setosa population were also measured. The data were comparated by linear Students Tests T and correlations. The parasitism performs a negative influence on size (height, basal diameter and circumference), vessel diameter, vessel element lenght and fiber lenght. On the other hand, parasited stems have the higher vessel frequency. The results show similar modifications on xylem architecture as observed on plants stressed by polution or drought. It seems that the theory of efficiency/safety can also be applied on the interpretation of parasitism, even considering that is a case of endoparasitism. The host responds to the parasite increasing the safety but keeping the total hydraulic conductivity at normal levels.¶

ASSUNTO(S)

pilostyles mimosa mimosa parasita anatomia vegetal parasite plant anatomy pilostyles

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