Diagnose de microbiólitos metálicos em espécies vegetais endêmicas em solos de rochas ultramáficas por microscopia eletrônica de varredura

Abstract

The aim of this paper is to investigate by SEM the presence of crystalline forms of noble metals in dehydrated tissues of Scutia buxifolia (Rhamnaceae), Scoparia montevidensis (Scrophulariaceae) and Adiantopsis cf. chlorophylla (Pteridaceae), a endemic vegetation on ultramafic soils from Pedras Pretas, São Sepé, southermost Brazil. Chemical composition of rocks, soils and ash plants were also determined by ICP-MS. The rocks and soils from Pedras Pretas show the expected geochemical pattern of ultramafic ones. Despite the low concentrations of some trace elements and noble metals in ash plants, the BSE images obtained by electron microprobe reveal the presence of semicrystals of Au, Pt, and Ag, besides Ni, Cr, Fe and Ca in xilem parenchyma cells from the species concerned. These preliminary data show the necessity of combination of mineralogical with biogeochemical and physiological investigations in order to demonstrate the importance of these plants in forming biominerals. Moreover, studies about metallic concentrations in plant tissues can contribute to the comprehension of detoxication mechanisms of plants that can be applied for phytoremediation purposes.