The precursor of ethylene synthesis in higher plants is

The precursor of ethylene synthesis in higher plants is Methionine.
Ethylene is a plant hormone and is produced from essentially all parts of higher plants, including leaves, stems, roots, flowers, fruits, tubers and seeds.
Plants synthesize ethylene using a two-step biochemical pathway starting from S-adenosyl-L-methionine (SAM). SAM is converted to 1-aminocyclopropane-1-carboxylic acid (ACC) by the enzyme ACC synthase (ACS). ACC is then converted to ethylene by the enzyme ACC oxidase (ACO). Thus Methionine can be called a precursor of this process.