The metabolism of methionine in higher plants.: Catabolism of the methyl group by seedlings of various species

Abstract

l-Methionine- 14CH 3 was rapidly metabolized after infiltration into pea, pumpkin, kohlrabi, and sesbania seedlings. In all cases the labeled carton atom was incorporated into the organic acid, neutral sugar, and amino acid fractions prepared from the seedlings after incubation with the radioactive methionine. Up to 4 per cent of the total activity fed was recovered as 14CO 2 after 24 hr. At this time as much as 30 per cent of the label was found in the organic acid fraction. In sesbania the activity in this fraction was localized in one compound primarily, whereas the other plants appeared to have two predominant products formed. Among the labeled components of the amino acid fraction, methionine, methionine sulfoxide, serine, and methyl methionine sulfonium were identified and were found in every species tested. The formation of methionine sulfoxide appeared to be a physiological process and not an artifact of the isolation procedure. The presence of the methyl sulfonium salt of methionine in every case implies that this compound may have a significant metabolic role in higher plants.