COMPARISON OF THE ONION PLANT (ALLIUM CEPA) AND ONION TISSUE CULTURE III. FEEDING OF ¹⁴C LABELLED PRECURSORS OF THE FLAVOUR PRECURSOR COMPOUNDS

Abstract

SUMMARYCallus and onion leaf tip material were exposed to ["C]cysteme, ["C]serine or ["Qvaline and the distribution of labelling in the amino acids and cysteine derivatives assessed after two to fourteen days. With ["C]cysteine and serine radioactivity vras found in the callus in a range of amino-acids and in the flavour precursor compounds, S-methyl-L-cysteine sulphoxide and 5-trans-prop-1-enyl-L-cysteine sulphoxide, particularly in the former precursor. ["C]valine was much more metabolically inert and little distribution of radioactivity occurred. In comparison the shoot tip showed a more active metabolism of ["CJserine and cysteine than callus but again much less activity with ['*C]valine, With all three compounds, however, the heaviest labelling in the shoot tip was in the cysteine derivatives, particularly the main flavour precursor of the intact onion, .S-trans-prop-1-enyl-L-cysteine sulphoxide. When unlabelled cysteine derivatives were fed to callus, S-trans-prop-t-enyl-L-cysteine sulphoxide was formed. The presence of this precursor compound in callus showed that the callus was capable of synthesizing 5-trans-prop-l-enyl-L-cysteine from early intermediates, such as the amino-acids, and by a pathway similar to that in the intact plant.

The biosynthetic pathway of the S-alk(en)yl-L-cysteine sulphoxides (flavour precursors) in species of Allium

“…More recently however, Ohsumi et al (1993) have shown that in differentiating tissue cultures of garlic AIICysSO is formed by the oxidation of AUCys in agreement with the pathways proposed by Suzuki et al (1961Suzuki et al ( , 1962, Sugii et al (1963), Granroth (1970 and Turnbull et al (1980). Thus there are two main pathways proposed so far for the synthesis of PrenCysSO.…”

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

“…It has been frequently reported that the major flavour precursor in onion, S-trans-prop-l-enyl-L-cysteine sulphoxide, was absent in tissue cultures of Allium cepa [126,127,153]. Yet the enzyme alliinase, which normally reacts with the precursor after damage to the tissue, was found to be present in the cultures.…”

Comparative Study on Allium schoenoprasum Cultivated Plant and Allium schoenoprasum Tissue Culture Organs Antioxidant Status

“…Tissue culture plants exhibited the highest activities in the roots in contrast to the cultivated plants where the highest activities were observed in the leaves (Štajner et al , ). Other authors stated also that the roots of Allium tissue culture showed very active metabolism (Turnbull et al , ).…”