Auxin Inhibition of Ripening in Bartlett Pears

Abstract

The effect of indoleacetic acid and 2, 4-dichlorophenoxyacetic acid on the ripening of intact mature-green pears (Pyrus communis var. Bartlett) was investigated using a vacuum infiltration technique.The effects of indoleacetic acid and 2, 4-dichlorophenoxyacetic acid at concentrations of 0.01, 0.1, and 1.0 mM each were studied on softening, degreening, and on ethylene and C02 evolution. Softening and degreening were inhibited increasingly in response to increased concentrations of indoleacetic acid.This inhibitory property was amplified by 2 ,4-dichlorophenoxyacetic acid at concentrations comparable to those of indoleacetic acid. Application of the auxins also prevented the climacteric rise in respiration, but stimulated ethylene synthesis. Despite the presence of elevated ethylene levels, the inhibitory auxin effect was predominant.It is proposed that endogenous auxins in fruit represent a resistance factor in ripening and must be inactivated before ripening can occur.It was proposed that endogenous factors in fruit resist the action of ethylene in the promotion of ripening (14). Auxins are among the naturally occurring constituents in fruit which could function as resistance factors in ripening (16). Consequently, it was suggested by Frenkel (9) that the decline in the level of auxins concomitant with ripening is required to sensitize fruit tissue to the action of ethylene gas. In order to verify the role of auxin as a resistance factor in ripening, the authors studied changes in ripening and in CO2 and ethylene evolution in Bartlett pears in relation to applied auxins. The results of this study indicate that auxin could overcome the action of ethylene and inhibit ripening in Bartlett pear.MATERIALS AND METHODS Pears (Pyrus communis var. Bartlett) at the mature green stage were obtained from the pear orchard of Rutgers University, New Brunswick, New Jersey. The fruits were treated with 10 jul/l ethylene for 12 hr at room temperature prior to auxin application.Solutions containing IAA or 2, 4-D were applied to the fruit by a modified vacuum infiltration procedure (10). Intact fruits were punctured through the central cavity from the calyx end with a 20-gauge needle and were submerged in the infiltration solution. Infiltration of the solutions was regulated by the vacuum setting at which the fruits were equilibrated prior 1 This study was supported in part by Hatch Funds. to infiltration (Fig. 1). Fruits were infiltrated at 5 ml/ lOOg tissue. Solutions used were 0.01, 0.1, and 1.0 mm of IAA or 2,4-D in combination with 0.3 M mannitol as a carrier solution (10). The resulting auxin concentration in the fruit tissue was one-twentieth of the auxin concentration in the infiltration solution. After infiltration the fruits were kept at room temperature, and samples were taken at intervals for measure-

Transcript Profiles of Auxin Efflux Carrier and IAA-Amido Synthetase Genes Suggest the Role of Auxin on Apple (<i>Malus</i> × <i>domestica</i>) Fruit Maturation Patterns

“…MdGH3.18 was highly expressed at the early stages but decreasing trend as fruit reached physiological maturity, which is opposite to the expression profile of MdGH3.18; and a much higher expression level was observed in CP than in GD. Auxin has long been considered a natural inhibitor for fruit ripening as the concentration of auxin is low during pear ripening [57]. It was also observed that as apple ripening began, auxin concentration decreased and ethylene concentration increased [58].…”

The fading distinctions between classical patterns of ripening in climacteric and non-climacteric fruit and the ubiquity of ethylene—An overview

“…'Bartlett', the changes in the patterns of free auxin and ABA were found to be remarkably similar (Frenkel 1975). Application of relatively higher concentrations of auxin delayed the maturation but at the same time it temporarily stimulates ethylene production (Frenkel and Dyck 1973;Frenkel 1975). These observations were parallel to the results obtained in grape which is a nonclimacteric fruit (Coombe and Hale 1973;Inaba et al 1976;Weaver and Singh 1978;Davies et al 1997;Baydar and Harmankaya 2005).…”

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

“…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.…”