THE BIOSYNTHETIC-PATHWAY OF THE S-ALK(EN)YL-L-CYSTEINE SULFOXIDES (FLAVOR PRECURSORS) IN SPECIES OF ALLIUM

Pulse labelling experiments with (CO42-)-C-35 fed for 24h to intact pl ants (shooted onion sets) of Allium cepa (onion) showed that > 70% of the label appeared in the S-alkenyl-L-cysteine sulphoxides within 18h, reached a maximum at 48h and thereafter decreased. The amount of labe l detected in the gamma-glutamyl peptide fractions was below 20% of th e total label at any time. It is concluded that in intact plants (at t he growth stage used) the gamma-glutamyl peptides are not the immediat e precursors of the S-alkenyl-L-cysteine sulphoxides. The major S-alke nyl-L-cysteine sulphoxide in onion was found to be compartmentalized m ainly within the endoplasmatic reticulum.