Effect of pH and Surface Charge on Cell Uptake of Auxin

Ruberv, P. H.; Sheldrake, A. R.

doi:10.1038/newbio244285a0

Cited by 120 publications

(72 citation statements)

References 23 publications

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“…As Rubery and Sheldrake (1973) have shown, the apparent pK for IAA, assuming that only undissociated IAA is taken up, is displaced some 0.5 pH units in the alkaline direction in organisms with cell walls containing fixed negative charges. From the data of Fig.…”

Section: Influence Of the Cell Wall Donnan Phasementioning

confidence: 85%

“…Tracer IAA was used; it will be shown that endogenous IAA does not interfere with the measurements. Particular attention is paid to the role of the cell wall Donnan phase in determining the concentrations of IAA and IAA" close to the plasmalemma (Bennett, 1955;Rubery and Sheldrake, 1973), and to the possible influence of transmembrane potential differences on IAA" distribution.…”

Section: Introductionmentioning

confidence: 99%

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TRANSPORT OF INDOLEACETIC ACID IN PLANT CELLS IN RELATION TO pH AND ELECTRICAL POTENTIAL GRADIENTS, AND ITS SIGNIFICANCE FOR POLAR IAA TRANSPORT

1975

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SUMMARYThe distribution of IAA between the vacuole and the bathing solution in Hydrodictyon africanum is consistent with passive entry of undissociated IAA and passive efflux of both undissociated IAA and of IAA", with Pi^^ (permeability coefficient)* about io~^ cms~^ and PIAA-about io~^ cms~^ The involvement of IAA~ in the efflux results from the inside-negative P.D. between the medium and the vacuole. The cytoplasm is at a higher pH than either the vacuole or the bathing solution used in most experiments; this is maintained by active H"*" efflux at the plasmalemma, and active influx at the tonoplast. In this situation the efflux of IAA" is further promoted by the increased concentration of IAA" in the relatively alkaline cytoplasm. Thus the apparent active efflux of IAA from these cells can be explained in terms of passive driving forces of concentration and electrical potential acting on IAA and IAA~, with the distribution of these two species dictated ultimately by PI^A, PIAA-> the pH of the various compartments and the electrical potential difference between them. If PIAA/^IAA-were larger at the apical than at the basal end of coleoptile cells, such an effect could explain polar IAA transport, with metabolic energy being used only to maintain the relative permeabilities to the two species, the pH gradient and the electrical gradient.

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Section: Influence Of the Cell Wall Donnan Phasementioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

TRANSPORT OF INDOLEACETIC ACID IN PLANT CELLS IN RELATION TO pH AND ELECTRICAL POTENTIAL GRADIENTS, AND ITS SIGNIFICANCE FOR POLAR IAA TRANSPORT

1975

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“…From Donnan principles, the pH in the cell wall itself cannot be exactly the same as that in a dilute liquid free space with which it is in equilibrium (20). Therefore, the pH values in these experiments do not strictly represent cell wall pH and will be referred to as free space pH values.…”

Section: Resultsmentioning

confidence: 99%

Rapid Auxin-induced Decrease in Free Space pH and Its Relationship to Auxin-induced Growth in Maize and Pea

Jacobs

Ray²

1976

Plant Physiol.

146

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A pH microelectrode has been used to investigate the auxin effect on free space pH and its correbtion with auxin-stimulated elongation in segments of pea (Pisum sativum) stem According to the currently popular acid secretion hypothesis of auxin action (2, 7), auxins stimulate growth by causing acidification of the cell walls, which at low pH undergo an increase in extensibility that leads to rapid cell enlargement. Several lines of evidence are consistent with this hypothesis (7,9,19,24), but published measurements of auxin-induced release of acid from tissue into an external bathing medium (3,10,11,18) have not shown that auxin stimulates H+ secretion quickly enough to account for the rapid response (17) of elongation to auxin. If the acid secretion theory is correct it must be demonstrable that following exposure to an auxin the pH in the cell wall space falls to an elongation-stimulating value by the time that observable elongation in response to auxin actually commences, i.e. within the latent period for auxin action on elongation. A pH microelectrode that permits this type of measurement (13) Arbor, Mich.) of exposed tip length of 5 Aim and tip diameter of 2 ,um. The reference electrode was a segment of glass tubing (80 x 1 mm) the end of which was drawn into a capillary with a tip diameter of a few ,um. This tube was filled with 3 M KCI, in which was immersed an AgCI-coated silver wire that connected to the reference terminal of the pH meter. The electrode was read using the mv mode of operation of the meter and was calibrated against phosphate-citrate buffers (50 mm in K-phosphate and Na-citrate) of pH 4 and 6 before and after each experiment.The relation between pH of a buffer solution and mv reading by the pH microelectrodes was checked for several microelectrodes with a series of solutions varying in pH from 4 to 7. Because this relation was always found to be linear over the pH range, mv readings from experiments were converted to pH values by linear interpolation using the mv values measured for the calibration buffers of pH 4 and 6.The sensitivity of a pH microelectrode varied, for different experiments, from 50 to 58 mv/pH unit, but it was always constant through a given experiment. Between the beginning and the end of a typical experiment, however, the absolute mv values recorded by the microelectrode for the two calibration buffers would often change by a few mv. This drift in value was always of the same magnitude and in the same direction for both calibration buffers. Thus, the sensitivity of the microelectrode did not drift. Although calibration of the microelectrode against buffers of known pH before and after each experiment allowed us to monitor microelectrode drift, we used only the results of the postexperiment calibration for conversion of microelectrode mv readings to pH values.

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“…According to the chemiosmotic model of auxin transport [11][12][13][14], a substantial portion of IAA is protonated in the apoplast and able to enter cells via bilayer diffusion, whereas IAA inside the cells is less protonated and its efflux requires active transport. As to our knowledge, whether this is completely so has never been proven experimentally.…”

Section: Auxin Transport Across Biological Membranesmentioning

confidence: 99%

Master and servant: Regulation of auxin transporters by FKBPs and cyclophilins

2016

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Plant development and architecture are greatly influenced by the polar distribution of the essential hormone auxin. The directional influx and efflux of auxin from plant cells depends primarily on AUX1/LAX, PIN, and ABCB/PGP/MDR families of auxin transport proteins. The functional analysis of these proteins has progressed rapidly within the last decade thanks to the establishment of heterologous auxin transport systems. Heterologous co-expression allowed also for the testing of protein-protein interactions involved in the regulation of transporters and identified relationships with members of the FK506-Binding Protein (FKBP) and cyclophilin protein families, which are best known in non-plant systems as cellular receptors for the immunosuppressant drugs, FK506 and cyclosporin A, respectively. Current evidence that such interactions affect membrane trafficking, and potentially the activity of auxin transporters is reviewed. We also propose that FKBPs andcyclophilins might integrate the action of auxin transport inhibitors, such as NPA, on members of the ABCB and PIN family, respectively. Finally, we outline open questions that might be useful for further elucidation of the role of immunophilins as regulators (servants) of auxin transporters (masters).

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Effect of pH and Surface Charge on Cell Uptake of Auxin

Cited by 120 publications

References 23 publications

TRANSPORT OF INDOLEACETIC ACID IN PLANT CELLS IN RELATION TO pH AND ELECTRICAL POTENTIAL GRADIENTS, AND ITS SIGNIFICANCE FOR POLAR IAA TRANSPORT

TRANSPORT OF INDOLEACETIC ACID IN PLANT CELLS IN RELATION TO pH AND ELECTRICAL POTENTIAL GRADIENTS, AND ITS SIGNIFICANCE FOR POLAR IAA TRANSPORT

Rapid Auxin-induced Decrease in Free Space pH and Its Relationship to Auxin-induced Growth in Maize and Pea

Master and servant: Regulation of auxin transporters by FKBPs and cyclophilins

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