Cold-induced ethylene biosynthesis is differentially regulated in peel and pulp tissues of 'Granny Smith' apple fruit

Ethylene biosynthesis and endogenous abscisic acid (ABA) concentrations were examined in commercially mature 'Granny Smith' apples during and following chilling exposure, in order to study the mechanism(s) leading to induction of ethylene biosynthesis in chilled fruit upon rewarming. The effects of exogenous ABA and ethylene during exposure to low temperature were also tested to assess the role of both growth regulators in the onset of increased ethylene biosynthesis upon removal from cold storage. Ethylene production rates, ACC oxidase (ACO) activity, ACC levels, presence of both ACO and ripening-related ACC synthase (ACS) proteins and endogenous ABA concentrations were monitored in both peel and pulp of fruit, based on previous results showing noticeable differences in maturation and ripening of both tissues in 'Granny Smith' apples. Remarkable differences were observed in the regulation of ethylene biosynthesis in peel and pulp of 'Granny Smith' apple fruit. ACO and ripening-related ACS were found to respond differentially to chilling and exogenous ethylene or ABA. It is suggested that increased endogenous ABA levels in the peel tissue might play a major role in cold-induced ethylene biosynthesis upon rewarming. This hypothesis would also imply a significant role for the peel tissue in climacteric ethylene biosynthesis. (C) 2003 Elsevier B.V. All rights reserved.