Biosynthesis and partitioning of individual glucosinolates between pod walls and seeds and evidence for the occurrence of PAPS:desulphoglucosinolate sulphotransferase in seeds of oilseed rape (Brassica napusL.)

Abstract

35 SO 4 2- and 35 S-labelled glucosinolate precursors were administered to intact whole-pods and seeds to investigate the capacity of oilseed rape (Brassica napus L.) pod tissues to carry out reactions of the glucosinolate biosynthetic pathway. 35 S-desulphobut-3-enyl and 35 S-desulphoindol-3-ylmethyl glucosinolates were converted to their sulphonated intact-glucosinolate homologues by isolated immature seeds. A neutral sulphur-containing fraction was isolated from pod walls and shown to be associated with glucosinolate biosynthesis. Further purification of this fraction showed the presence of desulphoglucosinolates, the penultimate intermediates in the glucosinolate biosynthetic pathway. Chemical characterization and quantification of these intermediates showed that their types and levels corresponded to the glucosinolate biosynthetic activity of pod-wall tissues. 'Partition quotients' (Pq) were calculated for individual glucosinolates from 35 S-labelling data and used to describe the apportionment of newly synthesized glucosinolates between pod walls and seeds. Results from continuous feeding studies with pods and 35 SO 4 2- indicated that individual rapeseed glucosinolates have characteristic Pq values.