Genetische und physiologische untersuchungen zur bildung von glucosinolaten in rapssamen: Lokalisierung des hauptbiosyntheseortes durch pfropfungen

Abstract

Summary Crossing experiments with the Brassica napus variety «Bronowski» (low in glucosinolate in seed) have shown (a) that high glucosinolate content of normal rape seed is inherited as a dominant character and that (b) the genotype of the embryo has no significant effect on quantity and composition of glucosinolates in seeds. This (quantity and composition of glucosinolates) depends on the genetic constitution of the mother plant, and indicates that the site of glucosinolate-biosynthesis is unlikely to be in seeds. Therefore we tried to localize the site of glucosinolate synthesis by grafting experiments using «Bronowski» (low glucosinolate) and «Zero erucic» (high glucosinolate). The main observations from reciprocal grafting studies were: 1. Whenever siliques or shoots of Zero Erucic were grafted on Bronowski, the quantity and composition (isothiocyanates and thiooxazolidones) of glucosinolates in seeds of the scion were identical with those of ungrafted Zero Erucic plants. Quantity and composition of glucosinolates in seeds of the stock were not influenced by the scion. These results indicated that (a) siliques (smallest grafting unit used in our experiments) are the main sites of biosynthesis for those glucosinolates which are stored in seeds, and that (b) the stock Bronowski is able to produce and transport to siliques all precursors needed for glucosinolate biosynthesis. Since we could not find any indication for an increased glucosinolate breakdown in Bronowski plants, it appeared that the low glucosinolate content of this genotype may be the result of a blocked glucosinolate biosynthesis. 2. In the reciprocal combination (when siliques and shoots of Bronowski were grafted on stocks of Zero Erucic) we found an increase in the final amount of glucosinolates in seeds of the scion. This was higher in seeds produced on grafted siliques than on grafted shoots. The composition of these glucosinolates which give rise to the increase, corresponded to the glucosinolate composition of seeds produced on Zero Erucic stock or on ungrafted Zero Erucic plants. This demonstrates that while most of the glucosinolates stored in seeds are synthesized in siliques, a part is synthesized also in other plant organs. The actual cause for the increase of glucosinolates could not however be determined. It is possible that either the glucosinolates themselves may be produced by the stock of Zero Erucic and translocated to the seeds of the Bronowski scion, or that some intermediate products may be translocated to the scion from which Bronowski is able to complete the biosynthesis of glucosinolates.