Optimization of ammonium acquisition and metabolism by potassium in rice (Oryza sativaL. cv. IR-72)

Abstract

We present the first characterization of K + optimization of N uptake and metabolism in an NH4

Rapid Ammonia Gas Transport Accounts for Futile Transmembrane Cycling under NH3/NH4 + Toxicity in Plant Roots

“…Compartmental analyses with 13 NH 3 / 13 NH 4 + in roots and shoots of plants grown under toxic (high-NH 3 /NH 4 + ) conditions generally yield extremely high "pool sizes" of many hundred millimolar (Britto et al, 2001b, leading to the speculation that the entire cell, not simply the cytosol, acts as a single compartment of tracer origin Balkos et al, 2010). This study provides the first evidence in support of this "whole-cell" hypothesis.…”

“…These effects were observed under both low (0.02 mM) and high (5 mM) external K + concentrations, which were applied in context of the known regulation of NH 3 /NH 4 + fluxes by K + (Szczerba et al, 2008;Balkos et al, 2010;ten Hoopen et al, 2010). Under low K + , where NH 3 /NH 4 + toxicity is most severe Balkos et al, 2010), total influx plateaued at approximately 200 mmol g -1 h -1 , the highest transmembrane flux of NH 3 /NH 4 + hitherto reported in any plant system. Under high K + , where relief from toxicity is observed , [NH 3 ] ext -dependent influx was significantly lower, as apparent in the decrease in V max (from 204.8 6 14.5 to 80.0 6 4.5 mmol g -1 h -1 for low-and high-K + plants, respectively).…”

“…One such mechanism might involve the modulation of AQP activity, which may well be expected, because, in plants, K + acquisition is the chief means of establishing osmotic balance and cell turgor Grzebisz et al, 2013). The effects of K + in the short-term suppression of NH 3 /NH 4 + influx and efflux (Szczerba et al, 2008;Balkos et al, 2010; see also Fig. 4) (Barker et al, 1967;Szczerba et al, 2008;Balkos et al, 2010) and thus pave the way for future studies.…”

“…The effects of K + in the short-term suppression of NH 3 /NH 4 + influx and efflux (Szczerba et al, 2008;Balkos et al, 2010; see also Fig. 4) (Barker et al, 1967;Szczerba et al, 2008;Balkos et al, 2010) and thus pave the way for future studies.…”

“…In this model, a rapid, thermodynamically passive influx of NH 4 + is coupled to an active efflux of NH 4 + that is nearly as rapid, constraining normal cellular function and energetics and resulting in plant growth decline and mortality. This phenomenon is thought to occur in NH 4 + -sensitive species such as barley (Hordeum vulgare) and, to a lesser extent, in tolerant species such as rice (Oryza sativa), which can be susceptible at higher thresholds (Balkos et al, 2010;Chen et al, 2013).…”