Inactivity of 3-Methyleneoxindole as Mediator of Auxin Action on Cell Elongation

Evans, Michael L.; Ray, Peter M.

doi:10.1104/pp.52.2.186

Cited by 23 publications

(12 citation statements)

References 16 publications

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“…It was concluded that the action of the applied compounds on ripening is a direct one, since the ripening rate exceeded the rate obtained by ethylene action alone at standard conditions or hypobaric storage. Although the role of the IAA-oxidation products in regulating auxin responses has been questioned (8,13), it is possible that these compounds may have a distinct regulatory function in plants. Viewed as related to the onset of ripening, the action of IAA oxidation products may not represent an auxin effect as was previously suggested (3,21) but rather an antiauxin effect, inasmuch as IAA retards ripening whereas IAA-oxidation products promote ripening.…”

Section: Resultsmentioning

confidence: 99%

Oxidative Turnover of Auxins in Relation to the Onset of Ripening in Bartlett Pear

Frenkél¹

1975

Plant Physiol.

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Pears (Pyrus communis var. Bartlett) kept in 100 % 02 showed an increase in the rate of softening, chlorophyll degradation, and ethylene evolution. The 02 application could overcome, in part, the inhibition of ripening by 1 mM indoleacetic acid. Ripening of pears was also accelerated by the application of solutions containing indoleacetic acid-oxidation products, obtained by an overnight incubation of 0.1 and 1 mM indoleacetic acid with traces of H202 and horseradish peroxidase. Although both treatments stimulated ethylene evolution, the promotion of ripening could not be attributed to an indirect ethylene effect. Indoleacetic acid oxidation products obtained in vivo by high 02 tensions or in vitro by enzymatic degradation may function in the promotion of fruit ripening and the synthesis of ethylene.Current evidence suggests that the onset of fruit ripening is subject to multihormonal control (7,19). Frenkel (9) emphasized the role of auxin turnover in the regulatory scheme, suggesting that fruit ripening is dependent, at least in part, on the decline in the activity of endogenous auxins. This concept is supported by results showing that ripening can be retarded by the application of auxins (11) and, conversely, can be initiated in pears by the application of an antiauxin (12), which serves to diminish the activity of auxins in fruit, thus relieving the inhibition of ripening from auxin action. It was further suggested that the depletion of auxins in the fruit can be attributed to an oxidative breakdown catalyzed by the activation of IAA oxidase at the onset of fruit ripening (9, 12).The present communication, dealing with the effect of oxidative metabolism of auxins in fruit as it relates to the onset of fruit ripening, suggests (a) that oxidative degradation may represent a mechanism for the inactivation of endogenous auxins in fruit and thereby the promotion of ripening, and (b) that the products resulting from the oxidative breakdown of auxins may function as regulatory factors in the enhancement of ripening. MATERIALS AND METHODSMature green pears (Pyrus communis var. Bartlett) were obtainied from an orchard located at the University of Massachusetts, Amherst.

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Section: Resultsmentioning

confidence: 99%

Oxidative Turnover of Auxins in Relation to the Onset of Ripening in Bartlett Pear

Frenkél¹

1975

Plant Physiol.

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“…Figure 2 shows the effect of 3-MeOx on the onset of ethylene synthesis. Whereas the untreated fruit (mannitol control) required 5 days to obtain the peak in ethylene evolution, pears treated with 0.1 AM 3-MeOx displayed a peak in ethylene evolution after 4 days. Those Under hypobaric conditions allowing the rapid removal of the ethylene synthesized by the fruit (3), the rate of softening was comparable to that of fruit kept under standard conditions.…”

Section: Materiails and Methodsmentioning

confidence: 99%

“…(mannitol control) (0), mannitol Pure preparations of 3-MeOx were obtained according to a method by Hinman and Bauman (10,11) as modified by Evans and Ray (4). The product was formed as yellow crystals (decomposition 225-235 C, cf.…”

Section: Materiails and Methodsmentioning

confidence: 99%

“…Some investigators reported that 3-MeOx can promote auxin-dependent responses in plants (2,12,15), although recent evidence disputes this contention, claiming that purified 3-MeOx preparations devoid of auxin activity could not promote auxin-mediated responses and that the auxin effect observed previously could be attributed to residual IAA in the 3-MeOx preparation (4). Other workers view 3-MeOx as a growth arrester (14), an inhibitor of auxin transport (2), or a modulator of IAA oxidase activity (9).…”

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confidence: 97%

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Promotion of Softening and Ethylene Synthesis in Bartlett Pears by 3-Methylene Oxindole

1975

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A purified preparation of 3-methylene oxindole (3-MeOx) was applied to Bartlett pears (Lyrus communis) by vacuum infiltration. The infiltrated fruit were kept at room temperature at atmospheric or at one-twentieth of an atmospheric tension. The rate of softening was markedly enhanced by the application of 0.1 and 1 ,uM 3-MeOx. At 10 AM 3-MeOx the promotive effect of the compound was diminished. All the employed concentrations of 3-MeOx exceeded the effect of applied ethylene. The enhancement of softening in fruit kept under hypobaric conditions suggests that the action of 3-MeOx is a direct one and not an indirect ethylene effect. 3-MeOx also showed stimulation in the onset of ethylene synthesis, shortening the time required to obtain the peak in ethylene synthesis from 5 days by the control to 3 days by 0.1 AM and 2 days by 1 jM of the applied compound. As with softening, 3-MeOx at 10 1M diminished the rate of ethylene synthesis.The results suggest that 3-MeOx could function as a senescence promoter in fruit. Also, since auxins retard ripening while 3-MeOx promotes ripening, the action of 3-MeOx may be considered as that of an auxin antagonist. The occurrence and the mode of action of 3-MeOx as a possible senescence factor in fruit are discussed.The biological role of 3-MeOx2 has been subject to debate since its discovery. Some investigators reported that 3-MeOx can promote auxin-dependent responses in plants (2,12,15), although recent evidence disputes this contention, claiming that purified 3-MeOx preparations devoid of auxin activity could not promote auxin-mediated responses and that the auxin effect observed previously could be attributed to residual IAA in the 3-MeOx preparation (4). Other workers view 3-MeOx as a growth arrester (14), an inhibitor of auxin transport (2), or a modulator of IAA oxidase activity (9). MATERIAILS AND METHODSMature green pears (Pyrus communis var. Bartlett) were used as the plant material for this study and were obtained from an orchard located in Amherst, Mass. 3-MeOx was applied to the fruit in a 0.3 M mannitol carrier solution using a vacuum infiltration method (7). The test solutions used consisted of a mannitol control (0 3-MeOx), mannitol control plus ethylene, and 0.1, 1, and 10 Mm of 3-MeOx. The fruit were infiltrated, on the average, with 5 ml of test solution/100 g tissue.The infiltrated fruit were kept at 21 C at atmospheric tension or in hypobaric storage at one-twentieth of an atmospheric tension to allow the rapid removal of endogenous ethylene in the fruit (3). The fruit under standard conditions were kept in glass jars and-ventilated with air at a rate of 400 ml/min. Chambers of 150 liter capacity were used to maintain hypobaric conditions. The chambers were ventilated with 100% 02 at a rate of 800 ml/min, thus allowing one-third of gas volume replenishment/hr.

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“…Hinman and Lang (6) reported that in the presence of peroxidase, the time required for the complete enzymic consumption of IAA at room temperature was less than 1 hr, whereas the formation of MOI, the end product of the peroxidase-catalyzed IAA oxidation pathway, continues for nearly 24 hr, indicating that the conversion of some of the intermediates (such as 3-hydroxymethyloxindole) to MOI was slow. On this basis, 18 units of peroxidase were added to a 5-ml medium consisting of 50 mM K-phosphate buffer (pH 6), 2% sucrose, and 100 jAM IAA and incubated at 27 C for exactly 1 hr such that all of the IAA was consumed as revealed by the Salkowski test (11), and various intermediates of IAA oxidation were accumulated without noticeable conversion of the intermediates to MOI.…”

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confidence: 99%

Inactivity of Oxidation Products of Indole-3-acetic Acid on Ethylene Production in Mung Bean Hypocotyls

Lau

John²,

Yang³

1978

Plant Physiol.

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The suggestion that indole-3-acetic acid (IAA)-stimulated ethylene production is assodated with oxidative degradation of IAA and is mediated by 3-methyleneoxindole (MOI) has been tested in mung bean (Phaseolus aureus Roxb.) hypocotyl segments. While IAA actively stimulated ethylene production, MOI and indole-3-aldebyde, the major products of IAA oxidation, were inactive. Tissues treated with a mixture of intermediates of IAA oxidation, obtained from a 1-hour incubation of IAA with peroxidase, failed to stimulate ethylene production. Furthermore, chlorogenic add and p-coumaric acid, which are known to interfere with the enzymic oxidation of IAA to MOI, had no effect on IAA-stimulated ethylene production. Other oxidation products of IAA, including oxindole-3-acetic acid, indole-3-carboxylic acid, (2-sulfoindole)-3-acetic acid, and dioxindole-3-acetic acid, were nil inactive. 1-Napbthaleneacetic acid was as active as IAA in stimulating ethylene production but was decarboxylated at a much lower rate than IAA, suggesing that oxidative decarboxylation of auxins is not linked to ethylene production. These results demonstrate that IAA-stimulated ethylene production in mung bean hypocotyl tissue is not mediated by MOI or other associated oidative products of IAA. Auxins have been well known to stimulate ethylene production in plant tissues (1). Recently, Frenkel et al. (7,8) reported that the onset of ethylene evolution in pears was associated with oxidative degradation of IAA, and MOI,4 a product of IAA oxidation, was effective in initiating ripening and ethylene synthesis in pears. They therefore proposed that auxins were senescence retardants while oxindoles, products of IAA oxidation, were senescence promoters. To understand the mechanism of auxin action on stimulated ethylene production it is important to determine whether IAA-induced ethylene production is caused by IAA per se or is due to the oxidation products of IAA. We have compared the effects of IAA and its oxidation products on ethylene production by mung bean hypocotyls. We have chosen mung bean hypocotyl, a vegetative tissue, rather than fruit tissue because it is known to respond more directly to IAA and has a shorter lag period than fruit tissue. Furthermore, vegetative tissues are not complicated by the ripening processes inherent in fruit tissue where the onset of ethylene evolution is always associated with ripening. MATERIALS AND METHODS Plant Materials. Seeds of mung bean (Phaseolus aurus Roxb.) were grown in vermiculite for 4 days in the dark at 24 C. Segments 2 cm long were cut from hypocotyls at a point 1 cm below the hook, as previously described (19). Unless otherwise specified, lots of 10 or 20 segments were incubated in 5 ml of a medium consisting of 50 mm K-phosphate buffer (pH 6), 2% sucrose, and various chemicals dissolved in water or ethanol as indicated, in a 50-ml Erlenmeyer flask. A plastic center well containing 0.2 ml of 40% KOH was hung in the flask to absorb evolved CO2. The flasks were sealed with rubber serum caps and ...

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Inactivity of 3-Methyleneoxindole as Mediator of Auxin Action on Cell Elongation

Cited by 23 publications

References 16 publications

Oxidative Turnover of Auxins in Relation to the Onset of Ripening in Bartlett Pear

Oxidative Turnover of Auxins in Relation to the Onset of Ripening in Bartlett Pear

Promotion of Softening and Ethylene Synthesis in Bartlett Pears by 3-Methylene Oxindole

Inactivity of Oxidation Products of Indole-3-acetic Acid on Ethylene Production in Mung Bean Hypocotyls

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