Grinstein and Rothstein 1986), near 135–145 mM, and even higher levels are routinely achieved in the renal system and in urine (Segen and Stauffer 1998). In mammals, blood serum Na + concentrations are held high, by virtue of strict homeostatic mechanisms (see e.g. Even in terrestrial animals, Na + has retained its role as an essential nutrient. It is instructive to ponder the evolution of early life in this salt-dominated environment, and it, thus, comes as little surprise that marine organisms, from protists to animals, are highly salt-tolerant, and indeed require Na + for survival. In the latter, it typically prevails at concentrations near 470 mM (Harris 1996 Epstein and Bloom 2005), and these can be higher still in areas of high evaporation and limited rainfall, such as regions near 30° latitude. Sodium is the sixth most abundant element in earth’s crust, where it comprises some 2.8 % (Lutgens and Tarbuck 2003), and, after chloride, is the second most abundant solute in the oceans. Our review investigates intriguing connections and disconnections between Na + nutrition and toxicity, and concludes that several leading paradigms in the field, such as on the roles of Na + influx and tissue accumulation or the cytosolic K +/Na + ratio in the development of toxicity, are currently insufficiently substantiated and require a new, critical approach. We examine connections between the nutritional and toxic roles throughout, and place special emphasis on the relationship of Na + to plant potassium (K +) relations and homeostasis. Here, we review the ion’s divergent roles as a nutrient and toxicant, focusing on growth responses, membrane transport, stomatal function, and paradigms of ion accumulation and sequestration. Following the principle of Theophrastus Bombastus von Hohenheim (Paracelsus), Na + is, however, beneficial to many species at lower levels of supply, and in some, such as certain C4 species, indeed essential. PLoS One 8, e66431.Sodium (Na +) is one of the most intensely researched ions in plant biology and has attained a reputation for its toxic qualities. Genomic analysis of stress response against arsenic in Caenorhabditis elegans. Sahu, S.N., Lewis, J., Patel, I., Bozdag, S., Lee, J.H., Sprando, R., and Cinar, H.N. Regulation of intracellular and mitochondrial sodium in health and disease. Mitochondria are intracellular magnesium stores: investigation by simultaneous fluorescent imagings in PC12 cells. Kubota, T., Shindo, Y., Tokuno, K., Komatsu, H., Ogawa, H., Kudo, S., Kitamura, Y., Suzuki, K., and Oka, K. Iron promotes protein insolubility and aging in C. Klang, I.M., Schilling, B., Sorensen, D.J., Sahu, A.K., Kapahi, P., Andersen, J.K., Swoboda, P., Killilea, D.W., Gibson, B.W., and Lithgow, G.J. Mitochondrial complex I function affects halothane sensitivity in Caenorhabditis elegans. Kayser, E.B., Morgan, P.G., and Sedensky, M.M. These data serve as reference concentrations for mitochondria isolated from young adult N2 utilizing the cited methods. ![]() ![]() It should be noted, however, that measured mitochondrial ion concentrations are influenced greatly by the method used for isolation caution should be exercised when interpreting relative ion concentrations. Mitochondrial Na concentrations are significantly higher than Ca concentrations in mammalian cells (Murphy and Eisner, 2009), and mitochondria can be a sink for magnesium (Kubota et al., 2005) as well as iron in mammals. Sodium (Na) was present in the highest concentrations compared to other elements (significantly higher than calcium (Ca), magnesium (Mg), iron (Fe), and manganese (Mn) One-way ANOVA with Tukey’s post-hoc test, *p≤0.05 means are denoted above each bar). Results were normalized to protein content (BCA assay). Samples were prepared by oven drying (95☌ overnight) and HNO3 digestion (90☌ for 4 h), followed by dilution with MilliQ water to a final HNO3 concentration of 3% prior to elemental analysis by ICP-MS. ![]() Elemental analysis of mitochondrial fractions was performed by inductively coupled plasma mass spectrometry (ICP-MS). Mitochondria were isolated from whole nematodes by dounce homogenization and differential centrifugation into a crude mitochondrial fraction as described (Kayser et al., 2004) with minor modifications. Briefly, 50,000 N2s were grown to young adult stage for mitochondrial isolation. This article provides reference concentrations of five essential ions present in the mitochondrial fraction of young adult N2 C. The content of these elements can both influence the effect of and be influenced by different stressors, including aging (Klang et al., 2014) and exposure to toxic chemicals (Sahu et al., 2013). Mitochondria are dynamic organelles that require a controlled balance of essential ions to perform critical functions within cells.
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