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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)
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)
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)
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)
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)
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)
Plant nutrient acquisition from concentrated soil solutions is governed by low-affinity transport systems in the plasma membranes of root cells. In this Opinion article, we illustrate that for six major nutrient ions, in addition to influx mediation by low-affinity transporters, high rates of ion cycling at the plasma membrane are a hallmark of nutrient(More)
Root growth in higher plants is sensitive to excess ammonium (NH(4)(+)). Our study shows that contact of NH(4)(+) with the primary root tip is both necessary and sufficient to the development of arrested root growth under NH(4)(+) nutrition in Arabidopsis. We show that cell elongation and not cell division is the principal target in the NH(4)(+) inhibition(More)