Morfoanatomia e composição mineral de raízes de duas espécies de restinga submetidas ao excesso de ferro / Morphoanatomy and mineral composition of roots from two species of restinga submitted to iron excess

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

In the south coast of Espírito Santo, Brazil, the restinga has received in the last years, an additional increment of iron, due to activities of iron ore industries. It was objectified to characterize the roots structure of the native restinga species, Ipomoea pescaprae L. (Convolvulaceae) and Canavalia rosea DC. (Fabaceae), with the iron plaque development; to verify the chemical composition of iron plaque and its effect in nutrients assimilation; to histolocalize the probable sites of iron accumulation in roots; and identify the morpho-anatomical symptoms caused by iron as a pollutant, in the root structure of these species. Seedlings of both species were grown in Hoagland nutrient solution, at pH 5.5, with and without excess of ferrous ion (150 mg / L Fe +2 as FeSO4.7H2O), ranging the exposure time (12, 36, 108 and 228 hours) after the application of iron. At the end of each exposure were collected lateral roots in both species, and root collar in C. rosea, for morpho-anatomical, histochemical and ultrastructural analysis, besides the quantification of iron in the plant and nutrient content in leaves and roots, extraction and chemical composition of the iron plaque. The lateral roots of the control treatment in the studied species presented white-brown coloration, without formation of iron plaque. After exposure to excess iron, it was verified alteration in the external morphology of these roots, as visual reduction in growth and emission of new roots, root flaccidity, absence of branching, besides a mucilaginous aspect and gray coloration in I. pes-caprae and orange in C. rosea. In I. pes-caprae roots there were intense browning in root apex, with necrosis followed by apex fall. C. rosea was the specie that accumulated more iron in the iron plaque. Among the species studied, when exposed to excess iron, there was no statistical difference in the translocation factor of iron to the aerial part. The root of both species presented the highest capacity for iron concentration, and the stem, the lowest. C. rosea presented the highest bioconcentration factor of iron in all organs. In the treatment with excess iron, the assimilation of Zn increased in C. rosea and the content of N reduced in the leaves of I. pes-caprae. In the treatments of exposure to excess iron for 12, 36 and 108 hours, it was not observed anatomical changes in the roots of both species. In both species there was a change in organization and shape of pericycle and cortex cells, and metaxylem did not complete its differentiation. In I. pes- caprae there were necrosis and collapse of lateral root primordiums and of the vascular cylinder. The cortex cells presented shrinkage of the protoplast, formation of a cicatrization tissue and cell collapse. In C. rosea there was alteration in the division and differentiation pattern of cortex cell and differentiation of pericycle cell. In scanning electron microscopy, the iron plaques were evident across the surface of the root, with irregular deposition pattern in both species. The iron was histolocalized in all root tissues of both species, in maximum iron exposition, corroborating with discoveries in quantification. The daily increment of iron on the restinga vegetation soil in the south coast of Espírito Santo, followed by assimilation and morpho-anatomical changes in roots, can compromise the physiology of these species.

ASSUNTO(S)

placa de ferro canavalia rosea hidroponia canavalia rosea iron hydroponics ipomoea pes-caprae botanica ipomoea pescaprae

ACESSO AO ARTIGO

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