Vol. 70 No: 2

Title:
Changes in Ethylene-Producing Capacity of Apple Fruit Tissues During Natural or Induced Senescence

Authors:
C. MAGNE and F. LARHER

pp: 307-314

Abstract:
Changes in the ethylene producing capacity of apple fruits (Malus domestica Borkh., cv. Granny Smith) slices were investigated during accelerated ageing. Excised discs incubated for 24 h at 28°C on an iso-osmotic sorbitol solution (pH 7.5) underwent a slight increase of ethylene production followed by a rapid drop. When 1-aminocyclo-propane-1-carboxylic acid (ACC) was added to the incubation medium at the onset of ageing treatment, ethylene production was promoted significantly within 4 h. However, the ethylene production declined dramatically thereafter and aged tissues did not respond to any additional ACC supply. Cycloheximide strongly reduced ethylene production in apple discs during the first hours of the treatment. In contrast, the application of cordycepin (transcription inhibitor) significantly accelerated the decline in ethylene production as ageing progressed. The data suggest that the concentration of ACC is the main factor limiting ethylene production in intact preclimateric tissues. Moreover, ethylene production during the 4 h following excision is, in part, the result of wound-induced protein synthesis. During this period, the ACC induced ethylene biosynthesis involves partially the synthesis of proteins. The addition of various protein synthesis inhibitors to the external medium revealed the involvement of a translational step in the wound response and of a transcriptional step in the response to ageing treatment. The loss of ethylene-producing capacity by apple slices upon ageing was related to membrane injury during treatment, as indicated by electrolyte leakage from the tissues. This feature might explain the post-climacteric drop in ethylene production exhibited by intact fruits, since natural senescence of whole fruits results in the loss of ethylene-forming ability and an increase in membrane permeability.

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