Genesis of Ethylene in Apples

Abstract

EVER since Kidd and West¹ showed that emanations from ripe apples stimulated unripe apples into the respiration climacteric, and Gane² proved that the active principle in these emanations was ethylene, search has been made for the origin of this ‘ripening hormone’. The search has been intensified in the past few years. Burg and Thimann³ state that “there is general agreement that ethylene production is restricted to the stage in the life of fruits during which ripening occurs”. They were unable to decide precisely the source of the ethylene, but suggested that it may be produced by the mitochondria. Later Burg⁴ concluded that the biosynthetic source of ethylene is not to be found in intermediates of glycolysis, acid metabolism or the direct oxidation pathways of sugars, although it may be formed fairly directly from sugars by an, as yet, unknown pathway. More recently, Burg and Burg⁵, using ¹⁴C-labelled, possible precursors of ethylene and apple tissue, concluded that, although ethylene formation is related to the metabolism of Krebs cycle acids as suggested by Wang et al.⁶, the relationship does not appear to be a direct one.