Studies of the Biochemical Background to Differences in Glucosinolate Content in Brassica napus L. III. Further Studies to Localize Metabolic Blocks

To localize the metabolic block(s) in the biosynthesis of glucosinolates in the Brassica napus L. cv. Bronowski, 5‐methylthiopentanal oxime‐1‐14C was synthesized and fed to this cultivar and cv. Regina II, which has average levels of glucosinolates. The aldoxime was as efficient as a precursor of 3‐butenylglucosinolate in both cultivars, but less efficient as a precursor of 2‐hydroxy‐3‐butenylglucosinolate in Bronowski. These results suggest that there is a block in the biosynthesis of 3‐butenylglucosinolate in Bronowski that is situated before the synthesis of the intermediate 5‐methylthiopentanal oxime, as well as a block in the hydroxylation step. The silique walls of Bronowski contained increased amounts of total sulphur and inorganic sulphate.