INFLUENCE OF NITROGEN AND SULFUR ON THE GLUCOSINOLATE PROFILE OF RAPESEED (BRASSICA-NAPUS L)

Clear influence of N and S applications on the profile of individual g lucosinolates in the seeds of winter oilseed rape (Brassica napus L) w as found in field experiments. The major effect of N was on the relati ve abundance of the four alkenyl glucosinolates. Increasing the N rate increased the relative proportion of 2-hydroxybut-3-enyl at the expen se of pent-4-enyl, and to a lesser extent, 2-hydroxypent-4-enyl, in th e double-low (low erucic acid and low glucosinolates) variety Cobra, b ut at the expense of but-3-enyl in the single-low (low erucic acid) va riety Bienvenu. The results strongly suggest that a high N supply favo urs 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 abundan ce of the alkenyl and indole groups as a whole. Sulphur deficiency dec reased the concentrations of the alkenyl glucosinolates more than thos e of the indole glucosinolates, whereas S application to a S-deficient crop resulted in a larger response in the alkenyl group than in the i ndole 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 glucosino late profile in rapeseed are discussed.