Regulation of Root Growth by Auxin-Ethylene Interaction

Chadwick, Arthur V.; Burg, Stanley P.

doi:10.1104/pp.45.2.192

Cited by 124 publications

(60 citation statements)

References 18 publications

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“…The pattern of IAA-induced growth inhibition ( Fig. 3) was similar to that reported previously (9). In roots treated with CFM + IAA (Fig.…”

Section: Resultssupporting

confidence: 75%

Auxin and the Response of Pea Roots to Auxin Transport Inhibitors: Morphactin

Gaither¹

1975

Plant Physiol.

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The auxin transport inhibitor methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (CFM), a morphactin, inhibits negative geotropism, causes cellular swelling, and induces root hair formation in roots of intact Pisum sativum L. seedlings. In excised pea root tips, CFM inhibits elongation more than increase in fresh weight (swell ratio = 1.3 at 20 /Am CFM). CFM growth inhibition was expressed in the presence of ethylene. (14)(15)(16)(23)(24)(25) indicates that some chemicals may inhibit auxin transport by interfering with auxin binding at auxin-specific receptor sites. CFM2 effects on geotropism, phototropism, apical dominance, and hypocotyl curvature correlate with the ability of this morphactin to inhibit auxin transport (6,7,18,20,21,27 then conducted in 10-liter desiccators as described elsewhere (8). Downward curvature of the root tips was measured at different time periods. After 24 hr, photomicrographs were made of freehand longitudinal sections taken from the elongation zones of the roots.Growth Studies and Ethylene Evolution. Ten terminal 5-mm sections from 3-day-old seedlings (roots 5-6 cm long) were incubated in sealed 125-ml Erlenmeyer flasks as described previously (8) except that 6 ml of an incubation medium (pH 5.2) containing 5 mm dibasic potassium phosphate, 2 mm citric acid, 1 mm Ca(NO,)2-4H20, 1 % sucrose (w/v), and appropriate concentrations of CFM or IAA were used. Ethylene evolution was assayed by gas chromatography using a flame ionization detector (1).Studies with '4C-CFM and "4C Auxins. Tissue sections were incubated as described above, except that the buffer also contained 9-'4C-CFM (10.4 mCi/mmole, Cela Merck, Ingelheim, Germany), 1-14C-IAA (8.9 mCi/mmole, New England Nuclear), or I-"4C-2,4-D (3.03 mCi/mmole, Tracerlab). Radioactivity in the incubation medium was determined by counting an aliquot by liquid scintillation. After a given incubation period, radioactivity in the gas phase was determined by bubbling a 10-ml gas sample into 3 ml of NCS tissue solubilizer, then counting by liquid scintillation. The solution was then filtered, and the tissue was rinsed with ice water. After blotting and weighing, the sections were placed in a scintillation vial containing 2 ml of NCS tissue solubilizer. The vial was shaken at 45 C at least 4 hr. The radioactivity which had accumulated in the sections was then determined by liquid scintillation counting.Metabolism of '4C-CFM was studied by homogenizing rinsed roots at 4 C in 5 ml of 50 mm potassium phosphate buffer, pH 6.8. The brei was extracted twice with 10 ml of chloroform. After evaporation of the chloroform under reduced pressure, the residue was dissolved in 50 kdI of acetone. This residue and 4C-CFM were co-chromatographed separately with unlabeled CFM on an Eastman silica gel sheet. After development in benzene-glacial acetic acid (4:1, v/v), the chromatogram was cut into 1-cm strips. Each strip was placed directly into a vial for counting of the radioactivity by liquid scintillation. RESULTSCFM rapidly inhibited the normal geotropi...

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“…The pattern of IAA-induced growth inhibition ( Fig. 3) was similar to that reported previously (9). In roots treated with CFM + IAA (Fig.…”

Section: Resultssupporting

confidence: 75%

Auxin and the Response of Pea Roots to Auxin Transport Inhibitors: Morphactin

Gaither¹

1975

Plant Physiol.

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“…We reasoned that root growth inhibition caused by ABA might correlate with its ability to increase ethylene production. We chose to study excised pea root tips because the effects of ethylene on the growth of this tissue have been thoroughly examined (4,5). This paper reports the anomalous result we found when we treated excised pea root tips with ABA, viz., that low concentrations of ABA stimulated elongation.…”

mentioning

confidence: 64%

Abscisic Acid Stimulates Elongation of Excised Pea Root Tips

Gaither¹,

Lutz²,

Forrence³

1975

Plant Physiol.

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ABSTRACTcaps and shaken gently in the dark at 23 C for different time periods. After incubation, roots were blotted, weighed, and measured. A similar protocol was followed for Lens culinaris L. cv. Medica, Phaseolus vulgaris L. cv. Red Kidney, and Zea mays L. cv. Early Sun Glow. In the initial experiments with pea, ethylene produced from the incubating root tips was assayed by gas chromatography using a flame ionization detector (1).Some of the experiments with pea were performed under aseptic conditions. All labware used had been autoclaved. After washing in sterile H20, the tissue sections were placed in incubation medium which had been passed through a sterile 0.2 ,um membrane.ABA is known to inhibit several physiological processes including root growth (3, 7). In taproots of intact pea seedlings treated with ABA, Tietz (1 1) reported the occurrence of ethylene-like responses (1), i.e., inhibition of elongation, swelling of epidermal cells, and induction of root hairs and lateral roots. Ethylene is a potent inhibitor of root growth (1), and ABA promotes ethylene production from a number of different plant tissues (1). We reasoned that root growth inhibition caused by ABA might correlate with its ability to increase ethylene production. We chose to study excised pea root tips because the effects of ethylene on the growth of this tissue have been thoroughly examined (4, 5). This paper reports the anomalous result we found when we treated excised pea root tips with ABA, viz., that low concentrations of ABA stimulated elongation.MATERIALS AND METHODS Pisum sativum L. cv. Alaska seed were imbibed for 6 hr, sown in moist vermiculite, and grown in the dark at 23 C. When the roots were 4 to 5 cm long, 10 terminal 5-mm sections were placed in 125-ml Erlenmeyer flasks containing 6 ml of buffer, pH 5.2. The buffer, with or without ABA (mixed isomers, Sigma Chemical Co.), contained 5 mm dibasic potassium phosphate, 2 mm citric acid, 1 mm Ca(NO3)2 4 H20, and 1 % (w/v) sucrose. The flasks were stoppered with vaccine

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“…In the subapex the decline in the free IAA level is paralleled by increased conjugation and decarboxylation of IAA, but is not necessarily dependent upon the exogenous IAA content, for the same rate of decline of free LAA occurs regardless of whether the tissue is placed in 3 ml or 15 ml of 10 ,4M 14C-IAA. Similarly, in pea roots the rate of decline of endogenous free IAA has been found to be independent of the external IAA pool size (10). The conjugation system in the subapex is much more active than that in the apex, whereas the decarboxylation system in the two tissues appears to be about equally active.…”

Section: Resultsmentioning

confidence: 92%

Mechanism of Auxin-induced Ethylene Production

1971

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Indoleacetic acid-induced ethylene production and growth in excised segments of etiolated pea shoots (Pisum sativum L. var. Alaska) parallels the free indoleacetic acid level in the tissue which in turn depends upon the rate of indoleacetic acid conjugation and decarboxylation. Both ethylene synthesis and growth require the presence of more than a threshold level of free endogenous indoleacetic acid, but in etiolated tissue the rate of ethylene production saturates at a high concentration and the rate of growth at a lower concentration of indoleacetic acid. Auxin stimulation of ethylene synthesis is not mediated by induction of peroxidase; to the contrary, the products of the auxin action which induce growth and ethylene synthesis are highly labile.It has been suggested that auxin may stimulate ethylene production by inducing the enzymes involved in the formation of the gas (1). This theory is based primarily upon the finding that inhibitors of protein and RNA synthesis prevent auxininduced ethylene production, and also on the observation that stimulation of ethylene production by auxin has a substantial lag period (1,5,7,18,19). Extracts of pea seedlings contain an enzyme that converts methional to ethylene in a cell-free system (20). The enzyme has been identified as a peroxidase (30), a protein which also catalyzes a number of other reactions including oxidation of IAA (13,14,26). The present study presents evidence which shows the peroxidase content not to play a role in the regulation of ethylene biosynthesis in pea seedlings. Growth, ethylene production, the endogenous IAA content, exogenous IAA level, and rate of metabolism of growth hormone were continuously determined and compared in an attempt to determine the mechanism by which auxin induces ethylene production. (29) which is approximately 100% efficient. The radioactivity remaining in the tissue after alcohol extraction was determined after squashing the sections and drying them on a planchet, under which condition self-absorption was negligible. Enzyme Assay for Ethylene Synthesis. Sections of subapical internodes or plumular hooks were homogenized in 50 mm potassium phosphate buffer at pH 7.8 (10 sections/ml), strained through cheesecloth, and centrifuged at lOOOg for 15 min. The preparation could be further purified by dialysis and ammonium sulfate precipitation as described by Ku et al. for the pea enzyme (20), but a variable loss in activity occurred at each step, making the crude extract preferable for quantitative studies. The resulting supernatant (enzyme preparation) was assayed in 5 ml of reaction mixture described by Yang (30), consisting of 10 mM potassium phosphate buffer (pH 7.8), 0.6 mm methional, 3 em manganese sulfate, 80 mm resorcinol, 2 ytM ethylenediaminetetraacetic acid, 80 fM sodium hydrogen sulfite, with 1 ml of enzyme extract. The mixture was incubated at 25 C in a 25-ml Erlenmeyer flask sealed with a vaccine cap, and typically 1-ml samples of air were withdrawn from the flask at 30-min intervals, and ethylene was ...

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Regulation of Root Growth by Auxin-Ethylene Interaction

Cited by 124 publications

References 18 publications

Auxin and the Response of Pea Roots to Auxin Transport Inhibitors: Morphactin

Auxin and the Response of Pea Roots to Auxin Transport Inhibitors: Morphactin

Abscisic Acid Stimulates Elongation of Excised Pea Root Tips

Mechanism of Auxin-induced Ethylene Production

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