Differentiation of Allium subgenera by cysteine sulphoxides and further amino acids

Abstract

The genus Allium (>800 species) has been divided into several subgenera, sections, species and subspecies [1]. Cysteine sulphoxides are most prominent amino acid derivatives of this genus. These substances are susceptible for the enzyme alliinase. Alllinase reaction and further non-enzymatic steps do result in volatile sulphur compounds, which exhibit various bioactivities, e.g., antibiotic activities. The pattern of cysteine sulphoxides is rather characteristic for some subgenera. For instance, the subgenus Melanocrommyum is characterized by different heteroaromatic cysteine sulphoxides, whereas the subgenus Cepa typically shows rather high amounts of isoalliin. In the now presented study, amino acids as well as cysteine sulphoxides have been analyzed as their corresponding o-phthaldialdehyde (OPA) derivatives. Besides the above mentioned differences in the pattern of cysteine sulphoxides, also further amino acids show some relations between their amounts and subgenera. Most prominent are differences in the content of L-arginine in different subgenera of the genus Allium. L-arginine is a valuable nitrogen storage compound in many angiosperms [2]. But this amino acid has been also found in some Allium species in high concentrations. As an example, the amount of L-arginine in Allium cepa L. was increased during the maturation process [3]. Further on, the amount of L-arginine in samples belonging to the subgenera Allium and Cepa was significant higher (p<0.05) as the amount of L-arginine found in the subgenus Melanocrommyum suggesting different mechanisms of nitrogen storage. These differences should allow chemo-taxonomical classification of subgenera.