Biosynthesis of Ethylene in Fruit Tissues

Abstract

Although methionine has been established as a precursor of ethylene (Baur and Yang, 1969a, 1969b; Burg and Clagett, 1967; Lieberman et al. 1966; Mapson et al. 1970), whether it is the major precursor in vivo or whether there are other precursors is still an open question. Several potential precursors of ethylene, such as ethanol, ethane, propionic acid and fumaric acid (which may directly or indirectly yield ethylene through dehydration, dehydrogenation or decarboxylation), and some representative intermediates of recognized metabolic pathways (including glycolysis, the Krebs cycle and the pentose phosphate cycle) were found to be inactive as ethylene precursors (Jansen, 1965). Other precursors of ethylene which have been suggested include β-alanine (Stinson and Spencer, 1969), ethionine (Shimokawa and Kasai, 1967), β-hydroxy-propionic acid (Varner, 1961), propionaldehyde (Lieberman and Kunishi, 1967) and linolenic acid (Lieberman and Mapson, 1964). We have shown that neither propionaldehyde nor linolenic acid was incorporated into ethylene by apple tissue (Baur and Yang, 1969a, 1969b). This paper presents evidence showing that β-alanine, β-hydroxypropionic and ethionine also do not serve as precursors of ethylene. Additional evidence which supports the view that methionine is the biological precursor of ethylene will be presented.