Embryos excised from the seed of rapeseed (Brassica napus L.) accumulated glucosinolate from the culture medium. Uptake was saturable, subject to inhibition, varied with the developmental stage of the embryo but correlated with the time of accumulation of glucosinolates In situ. It is suggested that a carrier-mediated transport system is operating in the developing embryo.During embryogenesis, glucosinolates accumulate in the seed of rapeseed (Brassica napus L). At maturity, the embryo comprises from 80 to 90% of the seed dry weight and is the site where most of the glucosinolates contained in the seed are located (7,14). The subcellular location of the glucosinolates within the embryo is not known for certain, although they are thought to be localized in globoid bodies associated with aleurone grains (17), structures which form within and eventually fill the vacuoles. Inheritance studies (7,14) and grafting experiments (9) have indicated that seed glucosinolate content is maternally controlled. Whether embryos have any synthetic capability, or simply act as a sink for glucosinolates synthesized in the pod or other plant parts, is not known.Immature rapeseed embryos germinate when removed from the seed if placed in nutrient medium or water (3). Precocious germination may be prevented by increasing the osmotic potential of the medium or by adding ABA (4, 5). Immature embryos cultured on high osmoticum develop normally in that they continue to synthesize and accumulate embryo-specific storage protein (4). This investigation presents evidence that immature rapeseed embryos cultured on high osmoticum do not synthesize and/or accumulate glucosinolates ifglucosinolates are absent from the culture medium, but can take up exogenously supplied glucosinolate in a carrier-mediated fashion. This ability to take up glucosinolate varies with development of the embryo, and may account for glucosinolate accumulation in situ. MATERIALS AND METHODS Plant MaterialsRapeseed (Brassica napus L. cv Golden) plants were grown in soil-free medium (15) Accumulation ExperimentsAccumulation of glucosinolate in situ was examined from 16 to 40 DAP2 by excising embryos from seeds at 2 to 4 d intervals. Accumulation of glucosinolates in vitro was examined by aseptically excising embryos from the seeds and culturing 10 per Petri plate (6 x 1.5 cm) in 5 mL of solid Monnier's culture medium (12) (filter sterilized, 0.4% agarose) according to the method of Crouch and Sussex (3) with and without the addition of 1.0 mm 2-propenyl-, 3-butenyl-, or benzylglucosinolate. Potassium salt of 2-propenylglucosinolate (sinigrin) was purchased from Sigma. The tetramethylammonium salts of 3-butenylglucosinolate and benzylglucosinolate were purified from the seeds of rapeseed (Brassica campestris L. cv R500) and nasturtium (Tropaeolum majus L.), respectively, by the method described by Hanley et al. (6). Each plate constituted a sample.Glucosinolate uptake by embryos over a 26 h period was examined by excising embryos from seeds, 10 to 20 per sample, an...

The plant hormone abscisic acid (ABA) has been implicated in the inception and maintenance of seed dormancy, while gibberellins promote dormancy breakage and germination in some species. We investigated whether osmotic stress induced secondary dormancy in Brassica napus L. is associated with changes in ABA sensitivity and metabolism, as well as changes in gibberellin levels. Seeds of two genotypes, one with low dormancy potential (LDP) and one with high dormancy potential (HDP) for secondary dormancy, were exposed to a dormancy-inducing osmotic treatment for up to 4 weeks and then germinated in the presence of increasing ABA concentrations. Even at relatively high concentrations of supplied ABA, germination of LDP seed was not inhibited, while relatively low ABA concentrations inhibited the germination of HDP seed after osmotic treatment. Fluridone was highly effective in suppressing secondary dormancy development in HDP seed, but had no effect on germinability in LDP seed. Despite the lack of differences in nonosmotically treated seed, ABA and ABA-glucose ester accumulated to higher levels, and gibberellin A 1 accumulated to lower levels, in HDP relative to LDP seed by the end of the osmotic treatment. Our findings indicate an association among ABA sensitivity, biosynthesis and accumulation, and secondary dormancy potential in B. napus seed.Résumé : L'acide abscissique (ABA), une hormone végétale, a été associé à l'établissement et au maintient de la dormance des graines, alors que la gibbérelline entraîne le bris de dormance et la germination, chez certaines espèces. Les auteurs ont vérifié si la dormance secondaire induite par un stress osmotique, chez le Brassica napus L., est associée avec des changements dans la sensibilité et le métabolisme de l'ABA, ainsi qu'à des changements des teneurs en gibbérelline. À cette fin, les auteurs ont utilisé les graines de deux génotypes, l'un avec un faible potentiel de dormance (LPD), et l'autre avec un fort potentiel de dormance (HPD), et ils les ont exposées à un traitement osmotique induisant la dormance allant jusqu'à 4 semaines, avant de les mettre à germer en présence de quantités croissantes d'ABA. Même en présence de fortes concentrations d'ABA ajoutées, la germination des graines LPD n'est pas inhibée, alors que des concentrations relativement faibles d'ABA inhibent la germination des graines HPD, après le traitement osmotique. Le fluridone est très efficace pour supprimer le développement de la dormance secondaire chez les graines HPD, mais reste sans effet sur la germination des graines LPD. En dépit de l'absence de différences chez les graines non traitées osmotiquement, l'ABA et le glucose ester d'ABA s'accumulent à des degrés plus élevés, et la gibbérelline A 1 à des degrés inférieurs, chez les graines HPD comparativement aux graines LDP, vers la fin du traitement osmotique. Les auteurs suggèrent qu'il existe une association entre la sensibilité, la biosynthèse et l'accumulation de l'ABA, et le potentiel de dormance secondaire, chez les graines du B. napus.

Hydrothermal pretreatments for loosening the hull of Westar canola (Brassica napus L.) to promote dehulling of the seeds were investigated. The samples tested had on average 14.5% hull on a mass basis. Conditioning treatments involved soaking the seeds in distilled water or exposing the seeds to saturated steam. The moistened seed was treated with one of the following drying methods: unheated‐air drying, infrared drying, and fluidized‐bed drying. The dried grain was milled in an abrasive dehuller to break the hulls loose. The hulls were removed from the mix by aspiration. The treated seeds yielded a minimum of 11.4% to a maximum of 14.9% of the seed mass as the hull fraction. Nontreated seeds yielded 9.4% of the seed mass in hull fraction after abrasive dehulling and aspiration. Among treatments, raising the moisture content of the whole seed from 6 to 15% by exposure to steam, followed by drying in a fluidized bed, resulted in the maximum percent dehulling efficiency. The hull fraction contained about 24% crude fiber, 18% oil, and 18% protein on a dry‐mass basis.