Possible role of pH gradient and membrane ATPase in the loading of sucrose into the sieve tubes

Nature ◽  
1977 ◽  
Vol 267 (5609) ◽  
pp. 369-370 ◽  
Author(s):  
ROBERT GIAQUINTA
Keyword(s):  
Ph Gradient ◽  
Membrane Atpase ◽  
Sieve Tubes

scholarly journals Role of phospholipid in the intermediate steps of the sodium-plus-potassium ion-dependent adenosine triphosphatase reaction

1975 ◽  
Vol 146 (3) ◽  
pp. 729-738 ◽  
Author(s):  
K P Wheeler
Keyword(s):  
Phosphatase Activity ◽  
Adenosine Triphosphatase ◽  
Atp Hydrolysis ◽  
Reaction Sequence ◽  
Single Extraction ◽  
Background Value ◽  
Dependent Atpase ◽  
Membrane Atpase ◽  
Normal Enzyme

The phosphorylation and dephosphorylation steps of the (Na-++K-+)-dependent ATPase (adenosine triphosphatase) (EC 3.6.1.3) reaction have been compared in ‘normal’, lipid-depleted and ‘restored’ membrane ATPase preparations. Partial lipid depletion was achieved by a single extraction with Lubrol W, and ‘restoration’ by adding pure phosphatidylserine. γ-32-P-labelled ATP was used for phosphorylation. The main findings were as follows. (1) Partial lipid depletion decreased but did not prevent Na-+-dependent phosphorylation, although it virtually abolished both Na-+-dependent and (Na-++K-+)-dependent ATPase activities. (2) ‘Restoration’ with phosphatidylserine produced an increment in phosphorylation that was the same in the presence and absence of added Na-+. (3) K-+ decreased the extent of Na-+-dependent phosphorylation of the depleted enzyme without producing a corresponding release of Pi. (4) K-+ rapidly decreased the extent of phosphorylation of the ‘restored’ enzyme to near-background value, with a concomitant release of Pi. (5) Na-+-dependent ATP hydrolysis was not restored. (6) The turnover of the ‘restored’ enzyme seemed to be higher than that of the ‘normal’ enzyme. The reaction sequence is discussed in relation to these results and the fact that the depleted enzyme retained about 50% of K-+-dependent phosphatase activity.

Epidermal Langerhans Cells Are Resistant to the Permeabilizing Effects of Extracellular ATP: In Vitro Evidence Supporting a Protective Role of Membrane ATPase

1993 ◽  
Vol 100 (3) ◽  
pp. 282-287 ◽  
Author(s):  
Giampiero Girolomoni ◽  
Maria Lucia Santantonio ◽  
Saveria Pastore ◽  
Paul R. Bergstresser ◽  
Alberto Giannetti ◽  
...  
Keyword(s):  
Langerhans Cells ◽  
Protective Role ◽  
Extracellular Atp ◽  
Membrane Atpase ◽  
Epidermal Langerhans Cells

Slime plugs do not inhibit surge flow in sieve tubes

1982 ◽  
Vol 60 (7) ◽  
pp. 1281-1284 ◽  
Author(s):  
Gregor F. Barclay
Keyword(s):  
P Protein ◽  
Heracleum Mantegazzianum ◽  
Sieve Tubes ◽  
Heracleum Sphondylium ◽  
Sieve Plates

Slime plugs, composed largely of P protein, on sieve plates in phloem of Heracleum mantegazzianum L. and Heracleum sphondylium Somm. and Lev. do not seem to be effective in preventing surge flow caused by loss of turgor, therefore calling into question the role of slime plugs in phloem.

scholarly journals Fructose Utilization and Phytopathogenicity of Spiroplasma citri

2000 ◽  
Vol 13 (10) ◽  
pp. 1145-1155 ◽  
Author(s):  
Patrice Gaurivaud ◽  
Jean-Luc Danet ◽  
Frédéric Laigret ◽  
Monique Garnier ◽  
Joseph M. Bové
Keyword(s):  
Type Strain ◽  
Wild Type Strain ◽  
Carbon Sources ◽  
Wild Type ◽  
Spiroplasma Citri ◽  
Companion Cells ◽  
Transmission Period ◽  
Sieve Tubes ◽  
Sucrose Loading

Spiroplasma citri is a plant-pathogenic mollicute. Recently, the so-called nonphytopathogenic S. citri mutant GMT 553 was obtained by insertion of transposon Tn4001 into the first gene of the fructose operon. Additional fructose operon mutants were produced either by gene disruption or selection of spontaneous xylitol-resistant strains. The behavior of these spiroplasma mutants in the periwinkle plants has been studied. Plants infected via leafhoppers with the wild-type strain GII-3 began to show symptoms during the first week following the insect-transmission period, and the symptoms rapidly became severe. With the fructose operon mutants, symptoms appeared only during the fourth week and remained mild, except when reversion to a fructose+ phenotype occurred. In this case, the fructose+ revertants quickly overtook the fructose¯ mutants and the symptoms soon became severe. When mutant GMT 553 was complemented with the fructose operon genes that restore fructose utilization, severe pathogenicity, similar to that of the wild-type strain, was also restored. Finally, plants infected with the wild-type strain and grown at 23°C instead of 30°C showed late symptoms, but these rapidly became severe. These results are discussed in light of the role of fructose in plants. Fructose utilization by the spiroplasmas could impair sucrose loading into the sieve tubes by the companion cells and result in accumulation of carbohydrates in source leaves and depletion of carbon sources in sink tissues.

Gastroduodenal mucus bicarbonate barrier: protection against acid and pepsin

2005 ◽  
Vol 288 (1) ◽  
pp. C1-C19 ◽  
Author(s):  
Adrian Allen ◽  
Gunnar Flemström
Keyword(s):  
Ph Gradient ◽  
Support Surface ◽  
First Line ◽  
Physiological Conditions ◽  
Neutral Ph ◽  
Primary Function ◽  
Gel Layer ◽  
Mucus Gel ◽  
And Control

Secretion of bicarbonate into the adherent layer of mucus gel creates a pH gradient with a near-neutral pH at the epithelial surfaces in stomach and duodenum, providing the first line of mucosal protection against luminal acid. The continuous adherent mucus layer is also a barrier to luminal pepsin, thereby protecting the underlying mucosa from proteolytic digestion. In this article we review the present state of the gastroduodenal mucus bicarbonate barrier two decades after the first supporting experimental evidence appeared. The primary function of the adherent mucus gel layer is a structural one to create a stable, unstirred layer to support surface neutralization of acid and act as a protective physical barrier against luminal pepsin. Therefore, the emphasis on mucus in this review is on the form and role of the adherent mucus gel layer. The primary function of the mucosal bicarbonate secretion is to neutralize acid diffusing into the mucus gel layer and to be quantitatively sufficient to maintain a near-neutral pH at the mucus-mucosal surface interface. The emphasis on mucosal bicarbonate in this review is on the mechanisms and control of its secretion and the establishment of a surface pH gradient. Evidence suggests that under normal physiological conditions, the mucus bicarbonate barrier is sufficient for protection of the gastric mucosa against acid and pepsin and is even more so for the duodenum.

The Critical Role of pH Gradient Formation in Driving Superconformal Cobalt Deposition

2018 ◽  
Vol 166 (1) ◽  
pp. D3167-D3174 ◽  
Author(s):  
Matthew A. Rigsby ◽  
Lee J. Brogan ◽  
Natalia V. Doubina ◽  
Yihua Liu ◽  
Edward C. Opocensky ◽  
...  
Keyword(s):  
Critical Role ◽  
Ph Gradient ◽  
Gradient Formation ◽  
Cobalt Deposition
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