![]() Special focus will also be brought to interactions between sodium and potassium, wherein much insight into mechanisms of growth and performance enhancement as well as impairment can be found.įrom beet to chocolate: the classic literature-Na + benefits are common Here, we will focus on the literature covering these beneficial effects in higher plants, with a special emphasis on the few mechanistic explanations that have emerged, and, in addition, on salient open questions in the otherwise more thoroughly researched area of sodium toxicity, in particular as they relate to, or emanate from, deliberations of the former. Only a few groups of terrestrial plants, the halophytes, have (re-)-acquired the ability to tolerate, and indeed thrive on, high-Na + media, while others, however, appear to have the ability to utilize the Na + ion for several key cellular processes and can benefit from sodium’s presence, as long as supply concentrations remain below osmotically challenging ones. Such concentrations are, however, frequently found, and exceeded, in soils, and this occurs rarely as a uniform distribution but is associated with much spatial heterogeneity (Bazihizina et al. By contrast, the majority of land plants, when exposed to concentrations similar to those found in the mammalian blood stream, let alone that of the oceans, suffers moderate to severe toxicity symptoms. 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. Sodium (Na +) is one of the most intensely researched ions in plant biology and has attained a reputation for its toxic qualities.
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