Auxin Relations in Roots

ÅBerg, Börje

doi:10.1146/annurev.pp.08.060157.001101

Cited by 76 publications

(23 citation statements)

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“…We confirmed the report that ABA inhibits elongation of excised lentil root sections (8,9). Elongation of pea root tips is inhibited by high concentrations and stimulated by low concentrations of IAA (2). This same dose response pattern is qualitatively similar to the dose response pattern exhibited by ABA-treated pea root tips (Fig.…”

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confidence: 75%

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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confidence: 75%

Abscisic Acid Stimulates Elongation of Excised Pea Root Tips

Gaither¹,

Lutz²,

Forrence³

1975

Plant Physiol.

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“…Application of IAA to roots invariably causes an inhibition of elongation (3). We have presented evidence (18) that auxinmediated ethylene production accounts for the inhibition in pea roots, just as it does in pea buds (16) and etiolated pea stems (11).…”

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confidence: 70%

Regulation of Root Growth by Auxin-Ethylene Interaction

1970

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A large portion of indoleacetic acid (IAA)-induced inhibition of excised root tips and virtually all such inhibition of intact roots are the result of IAA-dependent ethylene production. Under certain conditions an additional effect of IAA accounts for a small portion of the inhibition of excised root tips. Ethylene production in response to applied IAA is governed by the level of applied auxin found inside the root. Evidence is presented to confirm the participation of ethylene in the geotropic response of roots.Application of IAA to roots invariably causes an inhibition of elongation (3). We have presented evidence (18) that auxinmediated ethylene production accounts for the inhibition in pea roots, just as it does in pea buds (16) and etiolated pea stems (11). This paper presents additional data supporting the idea that ethylene is the normal intermediate in auxin-mediated root growth inhibition, both in intact plants and in excised root sections, and also that the gas plays a role in root geotropism. MATERIALS AND METHODSSeeds of Pisum sativum (var. Alaska) were germinated as previously described (18), and all manipulations subsequent to planting were carried out in dim green light to avoid phototrophic and photomorphogenic involvement.Studies on Tissue Sections. When the roots were 2 to 3 cm long, usually 48 hr after planting, apical 5-mm segments were removed with a two-bladed cutter. Ten of these apices and 2, 5, or 10 ml of medium containing 2% sucrose (w/v), 5 J.M CoC12, 5 mM potassium phosphate buffer (pH 6.8), and an appropriate concentration of IAA were sealed in a 125-ml Erlenmeyer flask by means of a vaccine cap and gently shaken (68 cpm through a 4-cm stroke) in the dark for a predetermined number of hours. In a few cases when very small amounts of evolved ethylene had to be measured, 25-or 50-ml micro-Fernbach flasks were used. At the end of an incubation the ethylene production was determined by gas chromatography (11) immersed in a solution containing an appropriate concentration of IAA for 3 to 5 min, drained briefly, and placed in a 6-liter desiccator in the presence or absence of applied ethylene. The initial length and weight of the radicals were determined from a sample taken before immersion treatment, and final values after 9 or 18 hr. Ethylene production was measured under similar conditions using tissue grown in 300-ml glass bell jars filled with moist vermiculite and treated with IAA by the technique described above. Geotropic Studies. Presoaked seeds were planted in moist vermiculite in plastic bins (25 x 6 x 6 cm) and allowed to germinate. When the roots had attained a length of about 2.5 cm, the bins were covered with perforated plastic tops and sealed in 6-liter desiccators, the roots remaining vertical throughout. The pressure in each desiccator was reduced to about 380 mm Hg with a water aspirator, an appropriate amount of CO2 or C2H4 was injected, and then air was admitted until atmospheric pressure was again attained. After a 10-min equilibration period the desiccators ...

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“…These swellings, which become covered with root hairs (12), largely compensate for the volume decrease, and as a result the fresh weight of many roots is not altered by IAA except at a very high concentration (2). Atuxin also does not decrease the dry weight, frequency of mitoses, or plastic extensibility of roots except at a "toxic" level, so it has been concluded that "the auxin inhibition of longitudinal growth is certainly not the result of a decreased intensity of the growth processes in general, but rather the ouitcome of a change in their course (2)". The same may be said of ethylene action, for the gas does not prevent auxin from stimuilating growth and respiration (8,10) ; instead it removes the restraint on radial expansion, cauising swelling of the cortical cells of the expanding zone (8,17), and little if any change in fresh and dry weight (9) or the number of mitoses (17).…”

Section: Methodsmentioning

confidence: 99%