Inhibition of Ethylene Biosynthesis by Aminoethoxyvinylglycine and by Polyamines Shunts Label from 3,4-[14C]Methionine into Spermidine in Aged Orange Peel Discs

The flux of radioactivity from 3,4-[(14)C]methionine into S-adenosyl-l-methionine (SAM), 1-aminocyclopropane-1-carboxylic acid (ACC), spermine, and spermidine while inhibiting conversion of ACC to ethylene by 100 millimolar phosphate and 2 millimolar Co(2+) was studied in aged peel discs of orange (Citrus sinensis L. Osbeck) fruit. Inhibition up to 80% of ethylene production by phosphate and cobalt was accompanied by a 3.3 times increase of label in ACC while the radioactivity in SAM was only slightly reduced. Aminoethoxyvinylglycine (AVG) increased the label in SAM by 61% and reduced it in ACC by 47%. Different combinations of standard solution, in which putrescine or spermidine were administered alone or with AVG, demonstrated clearly that inhibition of ethylene biosynthesis-at the conversion of SAM to ACC-by AVG, exogenous putrescine or exogenous spermidine, stimulated the incorporation of 3,4-[(14)C]methionine into spermidine.