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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)
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)
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)
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)
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)
Using 13NH,~ as a tracer, compartmental analyses for NH~-were performed in non-mycorrhizal roots of intact Picea glauca (Moench) Voss. seedlings at four different concentration regimes of external NH~ ([NH~-]o), i.e. 0, 10, 100, and 1500 I-tM. Three kinetically distinct compartments were identified, with half-lives of exchange of approximately 2 s, 30 s,(More)
The disruption of K(+) transport and accumulation is symptomatic of NH(4)(+) toxicity in plants. In this study, the influence of K(+) supply (0.02-40 mM) and nitrogen source (10 mM NH(4)(+) or NO(3)(-)) on root plasma membrane K(+) fluxes and cytosolic K(+) pools, plant growth, and whole-plant K(+) distribution in the NH(4)(+)-tolerant plant species rice(More)
The radiotracer 13N was used to undertake compartmental analyses for NO3-in intact non-mycor-rhizal roots of Picea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux,(More)
The existence of distinct high- and low-affinity transport systems (HATS and LATS) is well established for major nutrient ions. However, influx mediated by these systems is usually estimated using uniformly simple tracer protocols. Two (42)K radiotracer methods to measure potassium influxes in the HATS and LATS ranges in intact barley (Hordeum vulgare L.)(More)