Promotion of Growth and Hydrogen Ion Efflux by Auxin in Roots of Maize Pretreated with Ethylene Biosynthesis Inhibitors

Mulkey, Timothy J; Kuzmanoff, Konrad M.; Evans, Michael L.

doi:10.1104/pp.70.1.186

Cited by 77 publications

(42 citation statements)

References 15 publications

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“…It may not be directly related to the mechanism by which auxin promotes proton effiux from plant cells. Auxin is not known to enhance proton effiux from pea root cells, although it may do so in the steler region (17). Furthermore, a decrease in Km would lead to an increase in proton effiux only if the ATP concentration of the cell were suboptimal.…”

Section: Discussionmentioning

confidence: 99%

Auxin Regulation of a Proton Translocating ATPase in Pea Root Plasma Membrane Vesicles

Gabathuler¹,

Cleland²

1985

Plant Physiol.

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ABSTRACrPea root microsomal vesicles have been fractionated on a Dextran step gradient to give three fractions, each of which carries out ATP-dependent proton accumulation as measured by fluorescence quenching of quinacrine. The fraction at the 4/6% Dextran interface is enriched in plasma membrane, as determined by UDPG sterol glucosyltransferase and vanadate-inhibited ATPase. The vanadate-sensitive phosphohydrolase is not specific for ATP, has a K, of about 0.23 millimolar for MgATP, is only slightly affected by K' or Cl-and is insensitive to auxin. Proton transport, on the other hand, is more specific for ATP, enhanced by anions (NO3-> Cl-) and has a K. of about 0.7 millimolar. Auxins decrease the K., to about 0.35 millimolar, with no significant effect on the V,,,., while antiauxins or weak acids have no such effect. It appears that auxin has the ability to alter the efficiency of the ATP-driven proton transport.The plasma membrane of plant cells contains an ATPase which is responsible for the electrogenic export of protons to the apoplastic solution (26). Its activity can be studied with isolated, inside-out plasma membrane vesicles, since they can retain the ability to transport protons in response to MgATP (25,27,29 on wet filter paper. After 3 d, the apical (2 cm) tips of the roots were harvested.Isolation of Sealed Microsomal Vesicles. All procedures were carried out at 4°C. The roots were first chopped with a razor blade and then homogenized using a mortar and pestle in 1 ml/ g fresh weight of buffer 1 (6% [w/w] sorbitol, 3 mm EDTA, 0.1 % BSA, 25 mM Tris, 20 mM mercaptoethanol, pH 7.0, with Mes). The homogenate was strained through four layers ofcheesecloth, the residue was rehomogenized in 1 ml/g fresh weight of buffer I and refiltered. The total filtrate was centrifuged at 6,000g for 20 min. The supematant was then centrifuged at 1 l0,OOOg for 30 min (Rotor type 30, Beckman L5-50 centrifuge) to obtain the microsomal pellet. The pellet was resuspended in 5 ml of buffer I and layered over a discontinuous Dextran T70 gradient consisting of 7 ml of 10%, 7 ml of 6%, and 7 ml of 4% Dextran T70 (w/w) in buffer I. This was centrifuged at 70,000g for 2 h (Rotor SW 27). The membrane bands at the interfaces were removed with a Pasteur pipette (fraction A, 0/4% interface; B, 4/6%; C, 6/10%) and diluted with buffer 11 (4.5% sorbitol, 25 mm Tris, pH 7.0, with Mes). After centrifugation at 1 l0,OOOg for 30 min, each pellet was resuspended in buffer II (except where indicated) and was used immediately for enzyme and proton translocation experiments.Enzyme Assays. ATPase activity was assayed in 0.5 ml containing 25 mM Tris-Mes pH 7.0, 10 mm MgSO4, 0.1 mM ammonium molybdate, 1 mM NaN3, 0.067 to 2.5 mm NaATP, and salts as indicated. The presence of sodium ions in NaATP did not affect the results, as Tris-ATP gave identical results. Reactions were initiated by addition of membrane protein (10-50 jig). After 10 to 30 min at 30°C, the reaction was stopped with 1 ml ice-cold 0.5% ammonium molybdate + 0.1% SDS in 0.72 N H2SO...

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Section: Discussionmentioning

confidence: 99%

Auxin Regulation of a Proton Translocating ATPase in Pea Root Plasma Membrane Vesicles

Gabathuler¹,

Cleland²

1985

Plant Physiol.

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“…It has already been explained, to a first approximation, why net gravitropic bending is typically downward for roots although upward for shoots (5,20). However, these basic orientations are subject to physiological and nonphysiological modulations many of which remain poorly understood (16,19,22 showing that under these conditions (a) by 135 min radioactivity was accumulating linearly with time at the base of the hypocotyl, and (b) the amount of auxin applied was two orders of magnitude below that required to cause nonlinearity of radioactivity transported to the base with respect to radioactivity loaded.…”

Section: References Therein)mentioning

confidence: 99%

Auxin Asymmetry during Gravitropism by Tomato Hypocotyls

Harrison

Pickard²

1989

Plant Physiol.

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Gravitropic asymmetry of auxin was observed in hypocotyls of tomato (Lycopersicon esculentum Mill.) soon after horizontal placement: the ratio of apically supplied [3H]IAA collected from the lower sides to that from the upper sides was about 1.4 between 5 and 10 minutes. This was adequately early to account for the beginning of curvature. The auxin asymmetry ratio rose to about 2.5 between 20 and 25 minutes, and to 3.5 during the main phase of curvature. This compares reasonably well with the roughly 3.9 ratio for elongation on the lower side to elongation on the upper side that is the basis for the curvature. These data extend evidence that the Went-Cholodny theory for the mediation of tropisms is valid for dicot stems. Also consistent with the theory, an auxin asymmetry ratio of 2.5 was observed when wrong-way gravitropic curvature developed following application of a high level of auxin. In addition to reversing the asymmetry of elongation, the large supplement of auxin resulted in lower net elongation. Previous data established that ethylene is not involved in this decrease of growth as a function of increasing level of auxin.A large body of evidence has accumulated in support of the Went-Cholodny theory that phototropism and gravitropism are mediated by lateral migration of auxin (22,23

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“…Originally established for the auxin-promoted growth of shoot organs such as coleoptiles, this hypothesis has often been claimed for explaining root growth phenomena, including gravitropic bending, long before the discovery of expansins (Pritchard, 1994). It is founded on the observation that root growth can be enhanced by acid buffers (pH 2-4; Edwards and Scott, 1974;Evans, 1976) or fusicoccin-mediated cell wall acidification (Lado et al, 1976), and is accompanied by proton secretion in the growing zone (Mulkey and Evans, 1981;Mulkey et al, 1982;Peters and Felle, 1999). In apparent agreement with the acid growth hypothesis, application of auxin ($1 mM) stops root growth and causes alkalinization (Evans et al, 1980) and stiffening (Bü ntemeyer et al, 1998) of the cell walls in the growing zone.…”

Section: Oh and To Respond Tomentioning

confidence: 99%

Production of Reactive Oxygen Intermediates (O2 ˙−, H2O2, and ˙OH) by Maize Roots and Their Role in Wall Loosening and Elongation Growth

2004

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Cell extension in the growing zone of plant roots typically takes place with a maximum local growth rate of 50% length increase per hour. The biochemical mechanism of this dramatic growth process is still poorly understood. Here we test the hypothesis that the wall-loosening reaction controlling root elongation is effected by the production of reactive oxygen intermediates, initiated by a NAD(P)H oxidase-catalyzed formation of superoxide radicals (O 2•2 ) at the plasma membrane and culminating in the generation of polysaccharide-cleaving hydroxyl radicals (• OH) by cell wall peroxidase. The following results were obtained using primary roots of maize (Zea mays) seedlings as experimental material. OH, and to respond to• OH by wall loosening, in passing through the growing zone. Moreover, inhibitor studies indicate that• OH formation is essential for normal root growth.

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Promotion of Growth and Hydrogen Ion Efflux by Auxin in Roots of Maize Pretreated with Ethylene Biosynthesis Inhibitors

Cited by 77 publications

References 15 publications

Auxin Regulation of a Proton Translocating ATPase in Pea Root Plasma Membrane Vesicles

Auxin Regulation of a Proton Translocating ATPase in Pea Root Plasma Membrane Vesicles

Auxin Asymmetry during Gravitropism by Tomato Hypocotyls

Production of Reactive Oxygen Intermediates (O2 ˙−, H2O2, and ˙OH) by Maize Roots and Their Role in Wall Loosening and Elongation Growth

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