Significance of hydrogen ion transport in plant cells

1974 ◽  
Vol 52 (5) ◽  
pp. 1035-1048 ◽  
Author(s):  
J. A. Raven ◽  
F. A. Smith
Keyword(s):  
Plant Growth ◽  
Ph Regulation ◽  
Plant Cells ◽  
Atp Synthesis ◽  
Hydrogen Ion ◽  
Cytoplasmic Ph ◽  
Active Process ◽  
Bathing Medium ◽  
Ph Stat ◽  
Hydrogen Ion Transport

The literature on the value and variability of the pH of the cytoplasm and vacuole of plant cells, and of the bathing medium, is reviewed. It is concluded that the pH of the cytoplasm and the vacuole changes much less than that of the medium during plant growth, despite a number of essential processes which produce or consume large quantities of protons in the cell during growth. It is thus concluded that loss of excess H+ or OH− to the medium is a major feature of cell pH regulation. In general, the excretion of excess H+ or OH− is an active process, i.e. against a gradient of electrochemical potential.The biochemical 'pH stat' mechanism of Davies is briefly discussed as an alternative to active transport of H+ or OH−. It is concluded that the major and primary function of active H+ and OH− fluxes is the regulation of cytoplasmic pH. Secondary functions (such as chemiosmotic ATP synthesis, transport of other solutes, and morphogenesis) of the H+ or OH− transport are also discussed. The extent to which these processes can occur is limited by interference with the regulation of intracellular pH.

Relation between hydrogen ion secretion and oxygen uptake by gastric mucosa

1964 ◽  
Vol 206 (1) ◽  
pp. 218-222 ◽  
Author(s):  
J. G. Forte ◽  
R. E. Davies
Keyword(s):  
Gastric Mucosa ◽  
Acid Secretion ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Hydrogen Ion ◽  
Sodium Thiocyanate ◽  
Ph Stat ◽  
The Mean ◽  
Stat Method ◽  
Hydrogen Ion Transport

Bullfrog gastric mucosae were isolated, mounted between two glass chambers, and bathed with physiological salt solutions equilibrated with 5% CO2 and 95% O2. Oxygen consumption (qO2; measured polarographically) and acid secretion (qH+; pH stat method) were measured along with the transmucosal potential difference (p.d.) and current passing through the mucosa. Histamine (4 x 10–4 m) caused an increase in qH+ and qO2. In measurements on nine short-circuited mucosae the mean ratio for the ΔqH+/ΔqO2 was 2.1. Sodium thiocyanate (0.5–15 mm) caused a decrease in qH+ and qO2 and an increase in short-circuit current. These effects were reversible. The ratio of ΔqH+/ΔqO2 induced by thiocyanate varied from 5.0 to 12.0. Current (0.5 to 1.0 ma/cm2) passed through the mucosae, which reversed the normally observed p.d. to values between +70 and +240 mv (secretory side with respect to nutrient side in an external circuit), caused a decrease in qH+ and qO2; the average ΔqH+/ΔqO2 was approximately 13. Using either thiocyanate or electric current the ratio of the induced ΔqH+/ΔqO2 can really exceed 4.0, the electrochemical equivalent of oxygen, and thus if this extra oxygen provides the energy for the extra acid secretion these results invalidate a simple redox pump hypothesis of hydrogen ion transport by gastric mucosa.

Cytoplasmic pH regulation in phorbol ester-activated human neutrophils

1986 ◽  
Vol 251 (1) ◽  
pp. C55-C65 ◽  
Author(s):  
S. Grinstein ◽  
W. Furuya
Keyword(s):  
Metabolic Pathways ◽  
Phorbol Esters ◽  
Ph Regulation ◽  
Human Neutrophils ◽  
Hexose Monophosphate ◽  
Cytoplasmic Ph ◽  
Extracellular Acidification ◽  
Hexose Monophosphate Shunt ◽  
Activated Neutrophils ◽  
Cytoplasmic Acidification

Activation of neutrophils by 12-O-tetradecanoylphorbol-13-acetate (TPA) is accompanied by an initial cytoplasmic acidification, followed by an alkalinizing phase due to Na+-H+ countertransport. The source of the acidification, which is fully expressed by activation with TPA in Na+-free or amiloride-containing media, was investigated. The acidification phase was detected also in degranulated and enucleated cytoplasts, ruling out a major contribution by the nucleus or secretory vesicles. Cytoplasmic acidification was found to be associated with an extracellular acidification, suggesting metabolic generation of H+. Two principal metabolic pathways are stimulated in activated neutrophils: the reduction of O2 by NADPH-oxidase and the hexose monophosphate shunt. A good correlation was found between the activity of these pathways and the changes in cytoplasmic pH. Inhibition of superoxide synthesis prevented the TPA-induced cytoplasmic acidification. Moreover, activation of the hexose monophosphate shunt with permeable NADPH-oxidizing agents (in the absence of TPA) also produced a cytoplasmic acidification. Cytoplasmic acidification was also elicited by exogenous diacylglycerol and by other beta-phorbol diesters, which are activators of the kinase, but not by unesterified phorbol or by alpha-phorbol diesters, which are biologically inactive. The results suggest that the cytoplasmic acidification induced by phorbol esters in neutrophils reflects accumulation of H+ liberated during the metabolic burst that follows activation.

scholarly journals PI(3,5)P2 sows the seeds of plant growth

2012 ◽  
Vol 198 (2) ◽  
pp. 147-147
Author(s):  
Ben Short
Keyword(s):  
Plant Growth ◽  
Plant Cells ◽  
Polarized Growth

Phospholipid directs polarized growth by targeting actin-polymerizing formins to the cortex of plant cells.

Pyrophosphate as an alternative energy currency in plants

2021 ◽  
Vol 478 (8) ◽  
pp. 1515-1524
Author(s):  
Abir U. Igamberdiev ◽  
Leszek A. Kleczkowski
Keyword(s):  
Metabolic Pathways ◽  
Energy Efficient ◽  
Alternative Energy ◽  
Plant Cells ◽  
Atp Synthesis ◽  
Continuous Operation ◽  
Low Oxygen ◽  
Pyruvate Phosphate Dikinase ◽  
Oxygen Stress ◽  
Membrane Bound

In the conditions of [Mg2+] elevation that occur, in particular, under low oxygen stress and are the consequence of the decrease in [ATP] and increase in [ADP] and [AMP], pyrophosphate (PPi) can function as an alternative energy currency in plant cells. In addition to its production by various metabolic pathways, PPi can be synthesized in the combined reactions of pyruvate, phosphate dikinase (PPDK) and pyruvate kinase (PK) by so-called PK/PPDK substrate cycle, and in the reverse reaction of membrane-bound H+-pyrophosphatase, which uses the energy of electrochemical gradients generated on tonoplast and plasma membrane. The PPi can then be consumed in its active forms of MgPPi and Mg2PPi by PPi-utilizing enzymes, which require an elevated [Mg2+]. This ensures a continuous operation of glycolysis in the conditions of suppressed ATP synthesis, keeping metabolism energy efficient and less dependent on ATP.

scholarly journals Lactic acid secretion by human neutrophils. Evidence for an H+ + lactate- cotransport system.

1992 ◽  
Vol 100 (2) ◽  
pp. 341-367 ◽  
Author(s):  
L Simchowitz ◽  
J A Textor
Keyword(s):  
Lactic Acid ◽  
Steady State ◽  
Ph Dependence ◽  
Transport Systems ◽  
Human Neutrophils ◽  
Bathing Medium ◽  
Monocarboxylate Transport ◽  
Cotransport System ◽  
Ph Stat ◽  
Transport In Mitochondria

The pathway by which L-lactate (Lac) crosses the plasma membrane of isolated human neutrophils was investigated. The influx of [14C]Lac from a 2 mM Lac, 145 mM Cl-, 5.6 mM glucose medium was approximately 1.5 meq/liter of cell water.min and was sensitive to the organomercurial agent mersalyl (apparent Ki approximately 20 microM), to alpha-cyano-4-hydroxycinnamate (CHC), the classical inhibitor of monocarboxylate transport in mitochondria, and to UK-5099 (apparent Ki approximately 40 microM), a more potent analogue of CHC. Transport was also strongly blocked (greater than 80%) by 1 mM of either 3,5-diiodosalicylic acid, MK-473 (an indanyloxyacetate derivative), or diphenyl-amine-2-carboxylate, and by 0.4 mM pentachlorophenol, but not by 1 mM ethacrynic acid, furosemide, or the disulfonic stilbenes SITS or H2DIDS. One-way [14C]Lac efflux from steady-state cells amounted to approximately 6 meq/liter.min and was likewise affected by the agents listed above. Influx, which was membrane potential insensitive and Na+ independent, displayed a strong pH dependence: extracellular acidification enhanced uptake while alkalinization inhibited the process (pK' approximately 5.7 at 2 mM external Lac). The rate of [14C]Lac influx was a saturable function of external Lac, the Km being approximately 7 mM. Steady-state cells exhibited an intracellular Lac content of approximately 5 mM and secreted lactic acid into the bathing medium a a rate of approximately 4 meq/liter.min. Secretion was completely suppressed by 1 mM mersalyl which inactivates the carrier, leading to an internal accumulation of Lac. That the Lac carrier truly mediates an H+ + Lac- cotransport (or formally equivalent Lac-/OH- exchange) was documented by pH-stat techniques wherein an alkalinization of poorly buffered medium could be detected upon the addition of Lac; these pH changes were sensitive to mersalyl. Thus, the Lac carrier of neutrophils possesses several features in common with other monocarboxylate transport systems in erythrocytes and epithelia.

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