Search

The glucosinolates and glucosinolate breakdown products (GBPs) in the seeds of three types of mustard (root, stem, and leaf mustards) from a core collection of 50 cultivars were studied. Nine glucosinolates and ten GBPs were identified, with sinigrin and 2-propenyl isothiocyanate (SIN-ITC) being the dominant glucosinolate and GBP, respectively. Among the tested cultivars, the contents of total glucosinolates and GBPs ranged from 46.84 to 89.30 μmol g−1 FW and from 23.07 to 82.20 μmol g−1 FW, respectively. Leaf mustard had both the highest average levels of glucosinolates and GBPs (65.04 μmol g−1 FW and 55.97 μmol g−1 FW, respectively) and the greatest variation in total GBP content compared with root and stem mustards. L8 had the highest content of SIN-ITC (72.06 μmol g−1 FW). These findings indicate that mustard seeds, especially cultivar L8, can be good candidates for functional foods since they contain extremely high levels of SIN-ITC, a potent anti-carcinogenic isothiocyanate.

Metabolic profiling of glucosinolates and their breakdown products in sprouts of 22 Chinese kale (Brassica oleracea var. alboglabra, BOA) varieties were investigated by using high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). Relationships between glucosinolate metabolites and flavor of Chinese kale sprouts were also analyzed. Results showed that compositions and contents of both glucosinolates and their breakdown products varied greatly among different varieties of Chinese kale sprouts. Gluconapin and 4,5-Epithio-pentanenitrile were the dominant glucosinolate and glucosinolate breakdown product in Chinese kale sprouts, respectively. Gluconapin and glucobrassicin were significantly related to bitterness (r = 0.577, 0.648, respectively; p 0.05). BOA 1 and BOA 13, BOA 3 and BOA 10 are good candidates for future breeding programs since the former two varieties have light bitterness and pungency, and the latter two varieties contain high levels of glucosinolate breakdown products such as isothiocyanates and epithionitriles in sprouts.

Most known biological roles of the glucosinolate–myrosinase system depend on its functioning as a ‘chemical bomb’. This term describes chemical defences which are based on the accumulation of inert components in separate compartments and rapid release of large amounts of defensive chemicals through mixing of these components and their reaction with each other upon tissue disruption. The essential components of the ‘chemical bomb’ formed by the glucosinolate–myrosinase system are the water-soluble glucosinolates and their hydrolytic enzymes, myrosinases. The defensive chemicals released upon mixing of glucosinolates and myrosinases are the rather lipophilic, irritant and toxic isothiocyanates (mustard oils; reflected in the term ‘mustard oil bomb’) and their derivatives. In addition, so-called specifier proteins may promote the formation of alternative products such as nitriles and epithionitriles. As a consequence, tissue disruption typically leads to the release of complex mixtures of glucosinolate breakdown products. Apart from directly defensive roles (e.g., as toxins), the breakdown products may also be involved in indirect defences (e.g., as signals in tritrophic interactions). Besides glucosinolate breakdown upon tissue disruption, their turnover in intact tissue has been discussed to contribute sulphur and nitrogen for plant growth. In addition, breakdown of glucosinolates in nondisrupted tissue has been observed upon pathogen attack. This chapter summarizes the current knowledge on the protein components of the glucosinolate breakdown machinery and its compartmentation, highlights the relevance of different breakdown product types and their regulated formation, and discusses pathways and roles of glucosinolate breakdown in nondisrupted tissue.

Background The glucosinolate-myrosinase system is an activated chemical defense system found in plants of the Brassicales order. Glucosinolates are stored separately from their hydrolytic enzymes, the myrosinases, in plant tissues. Upon tissue damage, e.g. by herbivory, glucosinolates and myrosinases get mixed and glucosinolates are broken down to an array of biologically active compounds of which isothiocyanates are toxic to a wide range of organisms. Specifier proteins occur in some, but not all glucosinolate-containing plants and promote the formation of biologically active non-isothiocyanate products upon myrosinase-catalyzed glucosinolate breakdown. Results Based on a phytochemical screening among representatives of the Brassicales order, we selected candidate species for identification of specifier protein cDNAs. We identified ten specifier proteins from a range of species of the Brassicaceae and assigned each of them to one of the three specifier protein types (NSP, nitrile-specifier protein, ESP, epithiospecifier protein, TFP, thiocyanate-forming protein) after heterologous expression in Escherichia coli. Together with nine known specifier proteins and three putative specifier proteins found in databases, we subjected the newly identified specifier proteins to phylogenetic analyses. Specifier proteins formed three major clusters, named AtNSP5-cluster, AtNSP1-cluster, and ESP/TFP cluster. Within the ESP/TFP cluster, specifier proteins grouped according to the Brassicaceae lineage they were identified from. Non-synonymous vs. synonymous substitution rate ratios suggested purifying selection to act on specifier protein genes. Conclusions Among specifier proteins, NSPs represent the ancestral activity. The data support a monophyletic origin of ESPs from NSPs. The split between NSPs and ESPs/TFPs happened before the radiation of the core Brassicaceae. Future analyses have to show if TFP activity evolved from ESPs at least twice independently in different Brassicaceae lineages as suggested by the phylogeny. The ability to form non-isothiocyanate products by specifier protein activity may provide plants with a selective advantage. The evolution of specifier proteins in the Brassicaceae demonstrates the plasticity of secondary metabolism within an activated plant defense system.

The influence of light, temperature, sulphur and nitrogen as well as growth substance combinations were tested on glucosinolate content in embryo, cotyledon and callus culture of rape. It was found, that depending on these factors, the glucosinolate breakdown varied, and in most cases the 2-week-old cultures did not contain those compounds. Also in plantlets, which differentiated from the cotyledons and remained in the in vitro culture, as well as in the callus, the glucosinolates were not detected. Glucosinolate in Keim-, Keimblatt- und Kallusrapskulturen in Abhangigkeit von auseren Faktoren Es wurde der Einflus von Licht, Temperatur, Schwefel und Stickstoff sowie Kombinationen von Wachstumssubstanzen auf den Glucosinolatgehalt in Keim-, Keimblatt- und Kallusrapskulturen untersucht. Dabei wurde gefunden, das in Abhangigkeit von diesen Faktoren die Glucosinolatzersetzung schwankte. In den meisten Fallen enthielten 2 Wochen alte Kulturen diese Verbindungen nicht. Auch in Pflanzchen, die sich von den Keimblattern unterschieden und in der in vitro-Kultur verblieben, sowie im Kallus wurden keine Glucosinolate nach gewiesen.

Headspace volatiles collected from six Crucifer species of the two genera Brassica and Sinapis were investigated by GC/MS. A total of 34 compounds were identified from both whole plants and macerated plant parts. Typical cell-degradation compounds including alcohols, aldehydes and glucosinolate breakdown products were primarily found in macerate samples, while terpenes were detected almost exclusively in whole plants. Macerated buds generally contained higher amounts of nitriles and isothiocyanates than did macerated leaves. Several compounds here identified have, to our knowledge, not been previously reported in Brassica and Sinapis.

(1987). Antinutritional and Toxic Effects of Glucosinolates and Glucosinolate Breakdown Products in B. Campestrisvar. Toria in Rats. Human Nutrition. Food Sciences and Nutrition: Vol. 41, No. 3-4, pp. 213-223.