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Most higher plants develop severe toxicity symptoms when grown on ammonium (NH(4)(+)) as the sole nitrogen source. Recently, NH(4)(+) toxicity has been implicated as a cause of forest decline and even species extinction. Although mechanisms underlying NH(4)(+) toxicity have been extensively sought, the primary events conferring it at the cellular level are(More)
Ratios of ammonium (NH 4 ‡) to nitrate (NO 3 ±) in soils are known to increase during forest succession. Using evidence from several previous studies, we hypothesize that a malfunction in NH 4 ‡ transport at the membrane level might limit the persistence of early successional tree species in later seral stages. In those studies, 13 N radiotracing was used(More)
Sodium (Na) toxicity is one of the most formidable challenges for crop production world-wide. Nevertheless, despite decades of intensive research, the pathways of Na(+) entry into the roots of plants under high salinity are still not definitively known. Here, we review critically the current paradigms in this field. In particular, we explore the evidence(More)
The mechanisms involved in regulating high-affinity ammonium (NH4+) uptake and the expression of the AtAMT1 gene encoding a putative high-affinity NH4+ transporter were investigated in the roots of Arabidopsis thaliana. Under conditions of steady-state nitrogen (N) supply, transcript levels of the AtAMT1 gene and Vmax values for high-affinity 13NH4+ influx(More)
Inorganic nitrogen concentrations in soil solutions vary across several orders of magnitude among different soils and as a result of seasonal changes. In order to respond to this heterogeneity, plants have evolved mechanisms to regulate and influx. In addition, efflux analysis using (13)N has revealed that there is a co-ordinated regulation of all component(More)
Using the short-lived radiotracer 42K+, we present a comprehensive subcellular flux analysis of low-affinity K+ transport in plants. We overturn the paradigm of cytosolic K+ pool-size homeostasis and demonstrate that low-affinity K+ transport is characterized by futile cycling of K+ at the plasma membrane. Using two methods of compartmental analysis in(More)
Current models of potassium acquisition and cytochemical processes in plants assume that potassium concentrations in the cytosol ([K+]cyt) are maintained homeostatically at approximately 100 mM. Here, we use 42K radiotracer data in the model plant species Hordeum vulgare L. (barley) to show that this assumption is incorrect. Our study reveals that [K+]cyt(More)
Compartmental analysis with 13N was used to determine cytosolic nitrate (NO3 –) pools, and their turnover rates, in roots of intact barley (Hordeum vulgare L. cv Klondike) seedlings. Influx, efflux, flux to the vacuole and assimilation, and flux to the xylem, varied as much as 300-fold over a wide range of external NO3 – conditions. By contrast, the kinetic(More)