Micro-PIXE studies of Ni-elimination strategies in representatives of two families of beetles feeding on Ni-hyperaccumulating plant Berkheya coddii

Plants may use the ability to hyperaccumulate toxic metals in their defence against herbivores. Insects can counteract and feed on toxic plants. Among grazers of Ni-hyperaccumulating Berkheya coddii, some beetles tolerate Ni (Chrysolina clathrata, former name Chrysolina pardalina; Epilachna nylanderi). The adaptive mechanisms against Ni toxicity were studied in these species using micro-PIXE quantitative elemental mapping and by microscopy techniques. Distinct differences were found in mechanisms used for Ni-elimination in both species. Functional comparisons and quantification of data extracted from selected micro-areas in target organs responsible for metal circulation (digestive tract and Malpighian tubules) were made. Similar detoxification mechanism is used against metals through spheric granules, which in E. nylanderi are formed mainly in the midgut, while in C. clathrata in Malpighian tubules and midgut. Elemental maps showed positive correlations of Ni and Zn in Malpighian tubules of E. nylanderi without such effect in C. clathrata. Quantitative relations of K(+) and Cl(-) indicate higher osmotic pressure increasing reabsorption of water necessary for Ni transportation to the intestine lumen and further rejection outside the body. Copyright (C) 2011 John Wiley & Sons, Ltd.