SULFUR TURNOVER IN THE DEVELOPING PODS OF SINGLE AND DOUBLE LOW VARIETIES OF OILSEED RAPE (BRASSICA-NAPUS L)

Changes in the sulphur (S) concentrations in pod walls and seeds of th e double low variety Cobra and single low variety Bienvenu of winter o ilseed rape (Brassica napus L) were studied during pod development. Th e S concentration in the seeds of Cobra increased between 47 and 61 da ys after flowering and thereafter remained stable, whereas in Bienvenu seed S concentration was much higher initially and continued to incre ase throughout the sampling period (from 57 to 108 days after flowerin g). These differences in S concentration reflect different patterns of glucosinolate accumulation in the seeds. In contrast, there was a lar ge and progressive build-up of S in the pod walls of Cobra, such that at maturity the S concentration in the pod walls of Cobra was approxim ately double that of Bienvenu. A large and progressive accumulation of inorganic sulphate was found to be responsible for the build-up of S in the pod walls of the double low variety. Short-term feeding experim ents with terminal racemes showed that a smaller proportion of S-35 wa s translocated from the pod walls to the seeds in Cobra than in Bienve nu. However, the build-up of S in the pod walls of Cobra did not seem to result from a restricted translocation of glucosinolates, since in both varieties exogenously supplied allylglucosinolate was translocate d rapidly from the pod walls to the seeds. These results are therefore consistent with the hypothesis that pod walls are a major site for th e biosynthesis of glucosinolates present in the seeds, and a metabolic block in the pathway of glucosinolate biosynthesis is responsible for the low glucosinolate concentration in the seeds of double low variet ies, which consequently results in a large build-up of sulphate in the pod walls.