Influence of S and N application on seed yield and quality of a double low (low erucic acid and glucosinolate content) variety of winter oilseed rape (Brassica napus L) was examined in field experiments at both S-sufficient and Sdeficient sites. At the S-sufficient site, application of S had no significant influences on seed yield, yield components, seed protein and oil contents, and resulted in only a marginal increase in seed glucosinolate content. Application of N increased seed yield and protein content, but decreased oil content concurrently. A significant increase in seed glucosinolate content in response to the increasing N rate was obtained at this site, which was more noticeable in those treatments with applied S than without. In contrast, at the S-deficient site, there were significant interactions between S and N on seed yield, protein and glucosinolate contents. Increasing the N rate beyond 150 kg ha-' did not increase seed yield in the absence of applied S. However, with an application of 300 kg N ha-', seed yield increased by 10.7% with an application of 50 kg S ha-'. The effect of N on seed yield was achieved mainly through enhanced pod formation, and that of S through reduced pod abortion. Sulphur application also increased seed protein contcnt at the high N rate, and increased methionine content at the expense of aspartic acid. On average, a two-fold increase in seed glucosinolate content in response to an application of 100 kg S ha-' was obtained at the S-deficient site. Also, increasing the N rate decreased seed glucosinolate content in the absence of applied S, but increased it when S was applied. The interaction between S and N on seed glucosinolate content was explained in terms of the allocation of S towards primary and secondary metabolites within plants.

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Clear influence of N and S applications on the profile of individual glucosinolates in the seeds of winter oilseed rape (Brassica napus L) was found in field experiments. The major effect of N was on the relative abundance of the four alkenyl glucosinolates. Increasing the N rate increased the relative proportion of 2-hydroxybut-3-enyl at the expense of pent-4-enyl, and to a lesser extent, 2-hydroxypent-4-eny1, in the double-low (low erucic acid and low glucosinolates) variety Cobra, but at the expense of but-3-enyl in the single-low (low erucic acid) variety Bienvenu. The results strongly suggest that a high N supply favours the hydroxylation step from but-3-enyl to 2-hydroxybut-3-enyl. In contrast, the major effect of S appeared to be on the relative abundance of the alkenyl and indole groups as a whole. Sulphur deficiency decreased the concentrations of the alkenyl glucosinolates more than those of the indole glucosinolates, whereas S application to a S-deficient crop resulted in a larger response in the alkenyl group than in the indole group. The more sensitive response of alkenyl glucosinolates to the plant S status is probably due to the requirement of methionine in their biosynthesis, as compared with the indole glucosinolates which are derived from tryptophan. Implications for changes in the glucosinolate profile in rapeseed are discussed.

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