Rapeseed plants have been grown in soil-free culture with varying amounts of nitrogen fertiliser applied as nitrate, and with 50% of the nitrate-N exchanged for ammonium. The experiment was performed at two levels of sulphate fertiliser. Yield, protein content, glucosinolate content and amino acid composition were studied. The glucosinolate content was lower and the protein content was higher at a high level of nitrogen fertiliser. Exchange of 50% of the nitrate-N for ammonium caused no significant change in glucosinolate or protein content. The amount of glucosinolate was higher at the high sulphate level. There were no sulphur-nitrogen interactions. Content of total aspartic acid increased with nitrogen fertilisation, while total content of other amino acids did not change significantly with fertilisation.The effect of a wide variety of applications of sulphate fertiliser on glucosinolate and total amino acid content have been studied in a separate experiment. Although both protein content and methionine content were reduced at a low sulphate level, glucosinolate content was reduced considerably more.Experiments in the field revealed that although a reduction in glucosinolate content of rapeseed may be obtained from using fertilisers low in sulphur on sandy soils this does not seem possible on heavy soils. IntroductionSeed meals of rape (Brassica napus L.) and turnip rape (Brassica campestris L.) contain W 5 % protein in the dry matter with a well balanced amino acid composition.l According to Miller et aZ.1 the limiting amino acids from a nutritional point of view are isoleucine and methionine. Since methionine very often is limiting in proteins of vegetable origin, it is important to obtain as high a content of this amino acid as possible. A factor that is still more limiting for the use of these meals, however, is the content of glucosinolates. These substances can be hydrolysed by the enzymic system myrosinase, yielding sulphate, glucose and isothiocyanates, the last-mentioned compound and its secondary products being toxic to animals, causing for example goitre in non-ruminants.2 Other hydrolysis products, for example nitriles, have also been found.3 Studies of glucosinolate content in seed of rape and turnip rape as affected by variety and environment were made by Josefsson & Appelqvist.4 By fertiliser experiments in plastic boxes (containers), they showed that low applications of sulphate fertiliser resulted in a low content of glucosinolates in the seed, although the protein production approached normal quantities. Fields with light soils where the sulphur fertilisation had been kept on a low level gave samples with a glucosinolate content that was significantly lower than in samples from other fields.4In the studies of Josefsson & Appelqvist, no significant variation in glucosinolate content was found between different levels of nitrogen fertiliser. Trzebny5 found, however, in a study of field-grown material that a high level of nitrogen fertiliser caused a significantly lowered glucosinolate content. ...

A method has been developed for the quantiitative determination of isothiocyanates and oxazolidinethiones in enzymic digests of seed meals of rape (Br,issica napus) and turnip rape (B. campestris). Good precision has been obtained; relative standard deviation was *2% when the method was applied with macro-(1 g) as well as on micro-amounts (10 mg) of seed meal.In order to obtain optimum yields from the same digests, the seed and meal were treated with hot air and hot buffer solution, respectively. The time,'temperature/moisture relationship of seed treatment necessary to inactivate the myrosinase in rape seed is presented.The results obtained with this method demonstrate that the content of progoitrin in rape seed is considerably higher than that obtained by application of an earlier widely used method, e.g. 4.8 % in defatted seed meal of Matador winter rape, compared with an earlier figure of 3 . 1 %.Introduction Defatted meals of rape and similar cruciferous seed crops have a high protein content and a reasonably well balanced amino acid composition? However the large amounts of thioglucosides present, which yield isothiocyanates and oxazolidinethiones upon enzymatic hydrolysis, limit their use as feed. Plant breeding projects to obtain varieties with the lowest possible content of such compounds have been initiated.2 With Wetter's method39 for the assay of these products of hydrolysis, problems in reproducing the results on oxazolidinethione content in a given seed sample on different occalsions were experienced. Several authors have reported a broad pH optimum at 7 for the action of myrosinase on purified thiogluc0sides5.~ whereas Wetter found a pH optimum at 4 for isothiocyanate formation in the presence of rapeseed meals. Preliminary experiments showed a higher rate of isothiocyanate release from a seed meal slurry at pH 4 than at 7 whereas in aqueous solutions of methanol extracts of the same meal the rate was higher at pH 7 than at pH 4. Thus, it was considered essential that studies on the conditions for the release of isothiocyanates and oxazolidinethione from the parent thioglucosides should be undertaken. Furthermore, a less time-consuming method, adaptable to micro-quantities was desired. The results of these studies are presented in the present paper. A preliminary report covering the principles of this new method has been published elsewhere.7Structure of thioglucosides and various split products in rape and turnip rape seeds Through degradation of two natural thioglucosides, sinigrin and sinalbin,8 and total synthesis of another naturally occurring thioglucoside, glucotropaeolin,g Ettlinger & Lundeen provided conclusive evidence for the thioglucoside structure depicted in Fig. 1. The major thioglucosides in rape and turnip rape are gluconapin and p r~g o i t r i n .~ For gluconapin the R in Fig. 1 corresponds to CH2 = CH -CH2 -CHz -; for progoitrin it is CH2 = CH-CH(OH)-CHZ-. FIG. 1. Enzymatic hydrolysis of thioglucosides at pH 7Hydrolysis of pure thioglucosides at neutral pH by an enzyme preparat...

No abstract

Seed meals of winter and summer types of varieties of Brassica napus and B. campestris, grown at different localities and in different years, have been analysed for content of glucosinolates which produce oxazolidinethiones and volatile isothiocyanates upon enzymic hydrolysis. Considerable differences existed in amounts of glucosinolates between species and between winter and summer types of the same species. Varietal differences were relatively small in most of the material studied. Samples of the Polish summer rape variety Bronowski and selections from this variety, however, exhibited very low glucosinolate contents; this is probably genetically determined.Environmental variation generally amounted to & 15 % of the average value. Under certain environments, however, 65 % lower values than average were obtained.

The aim of the investigation was to study the differences in the metabolism of substances that are utilized in the synthesis of glucosinolates between the Brassica napus cv. Bronowski, which is very low in glucosinolate content, and a cultivar (cv. Regina II) that contains approximately average amounts of these compounds. By experiments in which the plants were grown in nutrient solutions supplied with sulphate‐35S, it was shown that the rate of sulphate uptake was similar in the two cultivars. No accumulation of intermediate metabolites could be demonstrated by autoradiography in Bronowski. Sulphate‐35S, methionine‐35S, methionine‐2‐14C, 2‐amino‐6‐(methylthio)caproic acid‐2‐14C, and S‐(β‐d‐glucopyranosyl)‐4‐pentenethiohydroximic acid (desulpho‐3‐butenylglucosinolate) (glucose‐U‐14C or 35S) were fed to shoots of the two cultivars. After incubation, the plant material was extracted with methanol. The extracts were separated into various fractions, and in some experiments glucosinolates or derivatives of their degradation products were isolated. When measuring the radioactivity of the various fractions or isolated products, the incorporation of radioactivity into glucosinolates was found to be poor in Bronowski from sulphate, methionine, and 2‐amino‐6‐(methylthio)caproic acid. Desulpho‐3‐butenyl‐glucosinolate was an efficient precursor of 3‐butenylglucosinolate in Bronowski, but a poor precursor of 2‐hydroxy‐3‐bute‐nylglucosinolate, which suggests a metabolic block at the hydroxylation step in this cultivar. In Regina II desulpho‐3‐butenylglucosinolate was a good precursor of both 3‐butenylglucosinolate and of 2‐hydroxy‐3‐butenylglucosinolate, which demonstrates that these glucosinolates may be synthesized without prior formation of the corresponding co‐methylthioalkyl glucosinolates and that the hydroxylation can take place after the formation of desulpho‐3‐butenylglucosinolate. The results indicate that the low glucosinolate content of Bronowski is caused by block(s) in the separate pathway leading to the biosynthesis of glucosinolates.