The Titrimetric Assay of H+Excreted byRicinus communisCultivated on NH4+-N Nutrient Media: The Effect of Ionic Strength and Nutrient Phosphate Concentration

Allen, C. R.; Allen, Simon

doi:10.1093/jxb/38.4.597

Cited by 16 publications

(5 citation statements)

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“…For carrot suspension cells, Carroll et al . (1994) provided evidence that excessive protons are removed by active buffering involving the GABA shunt, whereas Allen & Raven (1987) and Allen & Allen (1987) argued on the basis of a careful assessment of ion balances in Ricinus that intracellular pH was solely maintained by H + efflux. Contrasting results may be due to differences in the experimental system that was used (cell culture versus intact plant, including long‐distance transport).…”

Section: The Physiological Significance Of Net H+ Effluxmentioning

confidence: 99%

Biochemical and biophysical pH clamp controlling Net H⁺ efflux across the plasma membrane of plant cells

Wegner

Zhang

et al. 2021

New Phytologist

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Summary P‐type H+ ATPases mediate active H+ efflux from plant cells. They generate a proton motive force across the plasma membrane, providing the free energy to drive the transport of other solutes, partly by coupling to H+ influx. Wegner & Shabala (2020) recently suggested that passive H+ influx can exceed pump‐driven efflux due to ‘active buffering’, that is, cytosolic H+ scavenging and apoplastic H+ generation by metabolism (‘biochemical pH clamp’). Charge balance is provided by K+ efflux or anion influx. Here, this hypothesis is extended to net H+ efflux: even though H+ pumping is faster than backflow via symporters and antiporters, a progressive increase in the transmembrane pH gradient is avoided. Cytosolic H+ release is associated with bicarbonate formation from CO2. Bicarbonate serves as substrate for the PEPCase, catalyzing the reaction from phosphoenolpyruvate to oxaloacetate, which is subsequently reduced to malate. Organic anions such as malate and citrate are released across the plasma membrane and are (partly) protonated in the apoplast, thus limiting pump‐induced acidification. Moreover, a ‘biophysical pH clamp’ is introduced, that is, adjustment of apoplastic/cytosolic pH involving net H+ fluxes across the plasma membrane, while the gradient between compartments is maintained. The clamps are not mutually exclusive but are likely to coexist.

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Section: The Physiological Significance Of Net H+ Effluxmentioning

confidence: 99%

Biochemical and biophysical pH clamp controlling Net H⁺ efflux across the plasma membrane of plant cells

Wegner

Zhang

et al. 2021

New Phytologist

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“…According to Britto & Kronzucker (), amino acid synthesis with ammonium serving as N source is acidifying both the cytosol (in agreement with previous studies; Raven, ; Carroll et al ., ), and the apoplast (Allen & Allen, ).…”

Section: Biochemical Mechanisms Of Active Ph Buffering In Respiring Cmentioning

confidence: 99%

Biochemical pH clamp: the forgotten resource in membrane bioenergetics

Wegner

Shabala

2019

New Phytologist

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Summary Solute uptake and release by plant cells are frequently energized by coupling to H+ influx supported by the proton motive force (pmf). The pmf results from a stable pH difference between the apoplast and the cytosol, with bulk values ranging from 4.9 to 5.8 and from 7.1 to 7.5, respectively, in combination with a negative electrical membrane potential. The P‐type H+ ATPases pumping H+ from the cytosol into the apoplast at the expense of ATP hydrolysis are generally viewed as the only pmf source, exclusively linking membrane transport to energy metabolism. However, recent evidence suggests that pump activity may be insufficient to energize transport, particularly under stress conditions. Indeed, cytosolic H+ scavenging and apoplastic H+ generation by metabolism (denoted as ‘active’ buffering in contrast to the readily exhausted ‘passive’ matrix buffering) also stabilize the pH gradient. In the cytosol, H+ scavenging is mainly associated with malate decarboxylation catalyzed by malic enzyme, and via the GABA shunt of the tricarboxylic acid (TCA) cycle involving glutamate decarboxylation. In the apoplast, formation of bicarbonate from CO2, the end‐product of respiration, generates H+ at pH ≥ 6. Membrane potential is stabilized by K+ release and/or by anion uptake via ion channels. Finally, thermodynamic aspects of active buffering are discussed.

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“…NH4"'" uptake kinetics wer-e estir-nated by the depletion technique alter 7, 13 and 15 d. Between the depletion experin-rer-rts, NH4^ concentrations wcr-e kept in Ihe range of 40-50 x 10 ' mol m -\ Net H' release fr-om plants during NH4* uptake was estimated fror-n volumes of 100 mol r-n"' KOH and 10 n-rol n-r H2SO4 added to n-raintain a constant pH in the nutrient solution. Accor-ding to Allen & Allen (1987) this method underestir-r-rates H^ release by less Ihan 2-5%, assuming a constant alkalinity ofthe growth mediur-n. The alkalinity of the nutrient solutions as analysed by Gr-an-litr-ations (S0nder-gaar-d & Riemar-r 1979) remained at 0-77 eq m"thr-oughout the experir-r-rent.…”

Section: Ammonium Uptake Kinetics During Prolonged Growth At Differenmentioning

confidence: 99%

Effects of pH on ammonium uptake byTypha latifoliaL.

Dyhr-Jensen

Brix

1996

Plant Cell & Environment

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The effects of solution pH on NH4+ uptake kinetics and net H+ extrusion by Typha latifolia L. were studied during short‐term (days) and long‐term (weeks) exposure to pH in the range of pH 3.5–8.0. The NH4+ uptake kinetics were estimated from depletion curves using a modified Michaelis‐Menten model. T. latifolia was able to grow in solution culture with NH4+ as the sole N source and to withstand a low medium pH for short periods (days). With prolonged exposure (weeks) to pH 3.5, however, the plants showed severe symptoms of stress and stopped growing. The solution pH affected NH4+ uptake kinetics. The affinity for NH4+, as quantified by the half saturation constant (K1/2) and Cmin (the NH4+ concentration at which uptake ceases), decreased with pH. K1/2 was increased from 7.1 to 19.2 mmol m−3 and Cmin from 2.0 to 5.7 mmol m−3 by lowering the pH in steps from 8.0 to 3.5. Vmax was, however, largely unaffected by pH (∼22 μmol h−1 g−1 root dry weight). Under prolonged exposure to constant pH, growth rates were highest at PH 5.0 and 6.5. At pH 8.0 growth was slightly depressed and at pH 3.5 growth completely stopped. NH4+ uptake kinetics were similar at pH 5.0, 6.5 and 8.0 whereas at pH 3.5 NH4+ uptake almost completely stopped. The ratio between net H+ extrusion and NH4+ uptake decreased significantly at low pH. The adverse effects of low pH on NH4+ uptake kinetics are probably a consequence of a reduced H+‐ATPase activity and/or an increased re‐entry of H+ at low pH, and the associated decrease in the electrochemical gradient across the plasma membranes of the root cells.

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The Titrimetric Assay of H⁺Excreted byRicinus communisCultivated on NH₄⁺-N Nutrient Media: The Effect of Ionic Strength and Nutrient Phosphate Concentration

Cited by 16 publications

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Biochemical and biophysical pH clamp controlling Net H⁺ efflux across the plasma membrane of plant cells

Biochemical and biophysical pH clamp controlling Net H⁺ efflux across the plasma membrane of plant cells

Biochemical pH clamp: the forgotten resource in membrane bioenergetics

Effects of pH on ammonium uptake byTypha latifoliaL.

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The Titrimetric Assay of H+Excreted byRicinus communisCultivated on NH4+-N Nutrient Media: The Effect of Ionic Strength and Nutrient Phosphate Concentration

Cited by 16 publications

References 0 publications

Biochemical and biophysical pH clamp controlling Net H+ efflux across the plasma membrane of plant cells

Biochemical and biophysical pH clamp controlling Net H+ efflux across the plasma membrane of plant cells

Biochemical pH clamp: the forgotten resource in membrane bioenergetics

Effects of pH on ammonium uptake byTypha latifoliaL.

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The Titrimetric Assay of H⁺Excreted byRicinus communisCultivated on NH₄⁺-N Nutrient Media: The Effect of Ionic Strength and Nutrient Phosphate Concentration

Biochemical and biophysical pH clamp controlling Net H⁺ efflux across the plasma membrane of plant cells

Biochemical and biophysical pH clamp controlling Net H⁺ efflux across the plasma membrane of plant cells