Light-stimulated biphasic amino acid uptake by xylem parenchyma cells

Bel, Aart J. E. van; Schoot, Christiaan van der

doi:10.1016/0304-4211(80)90085-1

Cited by 21 publications

(3 citation statements)

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“…As already noticed in the studies on the mechanisms of sugar (6,8,19,21) and amino acid (4) uptake in various materials, these phenomena are transient. However, in some instances, long lasting (up to 48 h) alkalinizations have been recorded following the addition of amino acids to a medium containing Lycopersicon xylem parenchyma cells (29). Perfusing the hollow petiole of Ricinus with a solution containing 25 or 50 mm seine or alanine induces only a weak but long lasting decrease in the rate of acidification of the solution which normally occurs (1).…”

Section: Discussionmentioning

confidence: 99%

Energetics of Amino Acid Uptake by Vicia faba Leaf Tissues

Despeghel

Delrot²

1983

Plant Physiol.

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The uptake of IU-14Clthreonine and of by Viiafaba leaf discs is strongly pH dependent (optimum: pH 4.0) and exhibits biphasic saturation kinetics. Kinetics of a-AIB uptake at different pH values indicate that acidic pH values decrease the K., of the carriers while the maximal velocity remains nearly unaffected. Similar results were obtained for both system 1 (from 0.5 to 5 milmar) and system 2p(from 20 to 100 miDllma).After addtion of amino acids to a medium containng leaf fragments, alkalinizations depending both on the amino acid added and on its concentration have been recorded.The effects of compounds which increase (fusicoccin) or decrease (uncouplers, ATPase inhibitors, high KCI concentrations) the protonmotive force were studied both on the acidification of the medium and on amino acid uptake by the tissues. There is a close relationship between the time required for the effect of these compounds on the acidification and that needed for inhibition of uptake.Studies with thiol inhibitors show that 0.1 millmolar N-ethylmaleimide preferentially inhibits uptake by the mesophyll whereas 0.1 milimlar parachioromercuribenzenesulfonate affects rather uptake by the veins.New evidence was found which added to the electrophysiological data already supporting the occurrence of proton amino acid symport in leaf tissues, particularly in the veins.Mature leaves export sugars (mainly as sucrose) but also a broad spectrum of amino acids which may be translocated in substantial amounts. Although the mechanism of phloem loading of sucrose has been studied in some detail (7-10, 15, 16), little is known about the uptake of amino acid in leaf cells and particularly in phloem (3,12,25). Until now, most of the evidence suggesting that amino acids are co-transported with protons (and/or ions) comes from electrophysiological studies. For example, a transient depolarization of the membrane potential is recorded upon addition of amino acids to Lemna gibba fronds (14) and Avena coleoptiles (13,18). In the present paper, we have further tested the amino acid proton symport hypothesis by studying the effects of external pH and of various effectors of the protonmotive force on amino acid uptake and by recording proton fluxes linked to amino acid transport. Viciafaba (broadbean) leaves were selected because the lower epidermis can be removed easily, resulting in excellent contact and exchange between the apoplast and the incubation medium. The heterogeneity of the tissues under investigation necessitated measurements of net uptake of label as well as study of its distribution by autoradiography. In several cases, autoradiographs showed that the mesophyll and the veins ex-'This work was supported by the Centre National de la Recherche Scientifique (ERA 701).hibited a different sensitivity. a-AIB2 and threonine were used because preliminary studies revealed only a slight metabolism of these compounds in our material. MATERIALS AND METHODSPlant Material. Non-nodulated broadbean (Vicia faba cv Aguadulce), were grown under conditions...

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Section: Discussionmentioning

confidence: 99%

Energetics of Amino Acid Uptake by Vicia faba Leaf Tissues

Despeghel

Delrot²

1983

Plant Physiol.

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“…Van Bel [ 126,127] proposed that in Commelina the amino acids are maintained in the mesophyll by the high-affinity component, whereas the release near the conducting complex is mediated by the low-affinity system [125]. All tissues of tomato show biphasic [420] kinetics for alanine uptake [ 128,129]. Studies in more defined systems, i.e.…”

Section: Biochemical Studies Of Amino Acid Transportmentioning

confidence: 99%

Transporters for nitrogenous compounds in plants

et al. 1994

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“…Amino acids can enter the xylem in roots (2), and xylem-borne amino acids are exported from the xylem to the surrounding tissue (3). Uptake of amino acids into xylem parenchyma follows biphasic Michaelis-Menten kinetics suggesting that several transport systems with different kinetic properties are involved (4). Physiological studies show that large parts of amino acids fed directly into the xylem sap appear unchanged in the phloem sap, indicating that amino acids can be transported from xylem to phloem, thus leading to a cycling within the plant (5).…”

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confidence: 99%