Herbert J. Kronzucker

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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)
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)
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)
Using the short-lived radiotracer 42 K 1 , we present a comprehensive subcellular flux analysis of low-affinity K 1 transport in plants. We overturn the paradigm of cytosolic K 1 pool-size homeostasis and demonstrate that low-affinity K 1 transport is characterized by futile cycling of K 1 at the plasma membrane. Using two methods of compartmental analysis(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)
Futile plasma membrane cycling of ammonium (NH4+) is characteristic of low-affinity NH4+ transport, and has been proposed to be a critical factor in NH4+ toxicity. Using unidirectional flux analysis with the positron-emitting tracer 13N in intact seedlings of barley (Hordeum vulgare L.), it is shown that rapid, futile NH4+ cycling is alleviated by elevated(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)