Genetic Variation and Metabolism of Glucosinolates

Progress in the production and utilisation of oilseed rape (Brassica napus L. and B. rapa L.) and their derived products in the past years has resulted in the production of high-yielding double low varieties with low levels of erucic acid and glucosinolates. In order to meet this objective, extensive knowledge on the occurrence, structure and properties of glucosinolates and myrosinase isoenzymes (thioglucohydrolase; EC 3.2.1.147) co-occurring with glucosinolates is essential. The present chapter focusses on these subjects including heredity, genetic variation and metabolism of glucosinolates. A number of stages in the glucosinolate biosynthetic pathway are well known, but significant elements still remain to be further explored and elucidated. In recent years, most research has been confined on gene technology using Arabidopsis thaliana as a model and hence considering only the glucosinolates present in this particular plant. To date, more than 140 structurally different glucosinolates have been described of which similar to 30 glucosinolates occur in Brassica species. Only relatively few glucosinolates are produced in individual plant genera and/or families. Knowledge on the genetic and metabolic-based regulation of glucosinolate accumulation in different plants is therefore of great relevance in order to explain the reasons for the chemotaxonomically limited occurrence of structurally different glucosinolates. The metabolic regulation and thus the biological consequences of those changes are however unknown. Similarly, the reasons for the high selectivity of the multi-enzyme complexes towards the precursor amino acids in the biosynthesis of glucosinolates, as well as the specificity of the various enzymes needed for the modification of glucosinolate side chains and the substitution/esterification of the thioglucose residue of the molecules are yet to be clarified. The glucosinolate catabolism, which comprises the transformation of glucosinolates into various bioactive products, is another important area where limited information is available on the oligomeric myrosinase isoenzymes and associated compounds. This is especially relevant regarding the differences in the catalytic properties of the individual isoenzymes as well as the opportunities to modify these properties. New analytical methods allow for the synchronous detection of substrate and products in myrosinase-catalysed reactions, which broadens the perspectives for progress in this field.