COMPARISON OF THE ONION PLANT (ALLIUM CEPA) AND ONION TISSUE CULTURE. II. STIMULATION OF FLAVOUR PRECURSOR SYNTHESIS IN ONION TISSUE CULTURES

Abstract

SUMMARYOnion callus was exposed to high concentrations of a number of intermediates involved in the synthesis of S-fraw5-prop-l-enyl-L-cysteine sulphoxide, the major flavour precursor in the intact onion plant. The intermediates were sodium sulphate, L-valine, methacr\'lic acid and S-(2-carboxypropyl)-L-cysteine. Growth was reduced or totally inhibited at the highest concentration (50 to 100 mM) of all the intermediates but, except for methacrylic acid which was inhibitory at all concentrations, a limited growth occurred at the lower concentrations (10 to 20 HIM) of the other compounds. The only treatment which caused the callus to produce an onion odour on crushing the tissue was when S-(2-carboxypropyl)-L-cysteine was incorporated in the culture medium; this result indicated that the callus was capable of the final stages in the synthesis of S-fr<2W5-prop-l-enyl-L-cysteine sulphoxide. The presence of this pathway was confirmed by feeding smaller amounts of L-cysteine, L-valine and S-(2-carboxy-propyl)-Lcysteine (1 and 3 mM) and separating the amino acids and flavour precursors by t.l.c. electrophoresis. 5-^ram-prop-l -enyl-L-cysteine sulphoxide was found only when S-(2-carboxypropyl)-L-cysteine was present in the medium. When S-ethyl and S-propyl-L-cysteine were fed to the callus these compounds were oxidized to their sulphoxides showing that an oxidase system for the S-alkyl cysteines was present in the callus.

Production of essential oils and flavours in plant cell and tissue cultures. A review

“…In undifferentiated callus S-methyl-L-cysteine sulphoxide was present at a low concentration while the major precursor of onion flavour, S-trans-prop-l-enyl-L-cysteine was absent altogether [126,154]. But in undifferentiated roots and shoots this precursor was present again.…”

“…None of the monoterpenes characteristic of the essential oil of intact plants of M. spicata were found in callus cultures derived from this species. However, fatty acid methyl esters, free fatty acids, triterpenoids, triglycerides, phytosterols and squalene have been isolated from these cultures [127].…”

“…Addition of intermediates to the culture medium showed that the callus was capable of the final stages in the synthesis of S-trans-prop-l-enyl-Lcysteine sulphoxide [127].…”

Characterization and Immobilization of Purified Alliinase Produced from Shallots

“…The distilled liquid was mixed with petroleum ether thoroughly, then remained in the separatory funnel. The petroleum ether in the upper ether layer was recycled in the rotary evaporator at 40 º C. The flavouring precursor residue was dissolved in ethanol and stored at 4 º C. The flavouring chemicals were released from the flavouring precursors by free Alliinase and immobilized Alliinase following the method of Selby et al [13].…”

COMPARISON OF THE ONION PLANT (ALLIUM CEPA) AND ONION TISSUE CULTURE

“…The amino acid composition of onion and callus have already been compared (Selby, Galpin and Collin, 1979). The most notable difference was the absence of the main flavour precursor, S'-trans-prop-l-enyl-L-cysteine sulphoxide, from the callus.…”