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

Abstract

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.

Hydrogen Peroxide-mediated Oxidation of Indole-3-acetic Acid by Tomato Peroxidase and Molecular Oxygen

“…This is reflected in a shift in the IAA/02 ratio, which decreased with decreasing pH. This effect is seen even at pH 4 (24). The data in Table II oxidation.…”

Developmentally regulated expression of the wound‐ and pathogen‐responsive tomato anionic peroxidase in green fruits

“…The oxidative degradation of IAA catalyzed by peroxidases has been proposed to modulate auxin levels in plant tissues, thereby regulating their growth and development (Hare, 1964). The diminution of IAA in pears is believed to trigger the onset of ripening in this fruit (Frenkel, 1975). However, a similar role for tap in mediating the auxin levels of pre-climacteric tomato fruits has yet to be demonstrated.…”

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

“…During ripening of P. communis var. '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).…”

“…'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).…”