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

Abstract

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.

Citrus leaf abscission. Regulatory role of exogenous auxin and ethylene on peroxidases and endogenous growth substances

“…As the auxin activity drops in the explants, the activity of the inhibitor increases, A similar situation was observed in lentil roots (Gaspar, 1973) where tlie so-called inhibitor-/3 fraction was shown to contain at least methyleneoxitidole (Gaspar, Bouchet & Fries, 1972), the well-known oxidation product of IAA, Althougli ABA has been identified in the same fraction (Goldschmidt et al,, 1973), experiments are now being undertaken to clarify whetlier metliyleneoxindole is also present in tliis citrus fraction, Metliyleneoxindole has been proposed by Frenkel et al, (1975) to be involved in the control of ethylene biosynthesis. It is proposed as a working hypothesis tliat, in addition to tlie possible role of ABA in abscission, the decrease in auxin content in the second phase could be related to an endogenous ethylene formation induced by methyleneoxindole.…”

Involvement of Hydrogen Peroxide in the Regulation of Senescence in Pear

“…This results in the formation of IAA oxidation products which can promote senescence in fruit (6,11). The metabolism of this hormone may be an important factor in the regulation of senescence, and could account for some of the effects brought about by peroxides.…”

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

“…If oxidative degradation of IAA was associated with the onset of ethylene evolution and ripening fruit tissues as proposed by Frenkel and his co-workers (7,8) …”

“…However, in pear fruits Frenkel et al (7,8) have reported that it is the IAA oxidation products, but not IAA, which initiate ethylene production and ripening. The regulatory mechanism for the initiation of ethylene production in ripening fruit tissue is known to be different from that in vegetative tissue (1).…”

“…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.…”