Root Glucosinolate Profiles for Screening of Radish (Raphanus sativus L.) Genetic Resources

Optimization of cultivar, germination time and extraction for radish sprout extract with high sulforaphene content

BACKGROUND

Cruciferous vegetable sprout has been highlighted as a promising functional material rich in bioactive compounds called isothiocyanates (ITCs) and it can be grown in very short periods in controlled indoor farms. However, because ITCs content depends on multiple factors such as cultivar, germination time and myrosinase activity, those variables need to be controlled during germination or extraction to produce functional materials enriched in ITCs. Sulforaphene (SFEN), an ITC found primarily in radishes (Raphanus sativus L.), exerts beneficial effects on obesity. However, the optimal germination and extraction conditions for radish sprout (RSP) to increase SFEN content remain unascertained, and the extract's anti-obesity effect has yet to be evaluated.

RESULTS

The present study found that the SFEN content was highest in purple radish sprout (PRSP) among the six cultivars investigated. Optimal SFEN content occurred after 2 days of PRSP germination (2 days PRSP). To maximize the dry matter yield, total ITCs and SFEN contents in RSP extract, we found the optimal conditions for extracting PRSP [27.5 °C, 60 min, 1:75.52 solute/solvent (w/v), no ascorbic acid] using response surface methodology. Consistent with high SFEN content, 2 days PRSP extract significantly outperformed 3 days or 4 days PRSP extract in inhibiting lipid accumulation in 3T3-L1 cells. Moreover, 2 days PRSP extract suppressed adipogenesis and lipogenesis-related protein expression.

CONCLUSION

Regarding the cultivar, germination time and extraction conditions, optimally produced PRSP extract contains high SFEN content and exerts anti-obesity effects. Thus, we suggest PRSP extract as a potent functional material for obesity prevention. © 2024 Society of Chemical Industry.

Profiling of Health-Promoting and Taste-Relevant Compounds in Sixteen Radish (Raphanus sativus L.) Genotypes Grown under Controlled Conditions

It is becoming increasingly challenging to maintain crop yields and quality as the global climate changes. The aim of this study was to determine whether and how the profile of health-promoting and taste-related compounds of radishes changes within a growing season. A total of 16 radish (Raphanus sativus L.) genotypes that are commercially available on the Czech market were assessed by means of chemical analysis. Radishes were cultivated in three independent growing cycles under controlled conditions, and the effects of the genotype and growing cycle, as well as their interactions, on the chemical traits were evaluated. Most of the variability in chemical composition was associated with the growing cycle, which accounted for 51.53% of total variance, followed by the genotype (26% of total variance). The interaction between the growing cycle and genotype explained 22.47% of total variance. The growing cycle had the strongest effect on amino acid profiles. More specifically, the amino acids that are known to contribute to overall taste (glycine, along with glutamic and aspartic acids) showed the highest degree of variation, while the amino acids related to glucosinolate biosynthesis (methionine, isoleucine, tryptophan, and phenylalanine) showed relatively low variability. On the other hand, indole glucosinolates were found to differ the most between genotypes.

Dynamic profiling of intact glucosinolates in radish by combining UHPLC-HRMS/MS and UHPLC-QqQ-MS/MS

Glucosinolates (GSLs) and their degradation products in radish confer plant defense, promote human health, and generate pungent flavor. However, the intact GSLs in radish have not been investigated comprehensively yet. Here, an accurate qualitative and quantitative analyses of 15 intact GSLs from radish, including four major GSLs of glucoraphasatin (GRH), glucoerucin (GER), glucoraphenin (GRE), and 4-methoxyglucobrassicin (4MGBS), were conducted using UHPLC-HRMS/MS in combination with UHPLC-QqQ-MS/MS. Simultaneously, three isomers of hexyl GSL, 3-methylpentyl GSL, and 4-methylpentyl GSL were identified in radish. The highest content of GSLs was up to 232.46 μmol/g DW at the 42 DAG stage in the 'SQY' taproot, with an approximately 184.49-fold increase compared to the lowest content in another sample. That the GSLs content in the taproots of two radishes fluctuated in a similar pattern throughout the five vegetative growth stages according to the metabolic profiling, whereas the GSLs content in the '55' leaf steadily decreased over the same period. Additionally, the proposed biosynthetic pathways of radish-specific GSLs were elucidated in this study. Our findings will provide an abundance of qualitative and quantitative data on intact GSLs, as well as a method for detecting GSLs, thus providing direction for the scientific progress and practical utilization of GSLs in radish.

Metabolomic approach of azole fungicides in radish (Raphanus sativus): Perspective of functional metabolites

Azole fungicides is one of the major fungicides in agricultural field. In this study, toxic effects of diniconazole (DIN), metconazole (MET), and tebuconazole (TEB) to radish leaves and roots were investigated using targeted metabolomics with gas chromatography-mass spectrometry (GC-MS/MS). Especially, the changes of functional chemicals, including phytosterols and glucosinolates evaluated. Radish leaves and roots were harvested after 7 days and 14 days from last exposure. In multivariate analysis, the experimental groups showed clear separation in PCA and PLS-DA score plots. Phytosterols and glucosinolates were significantly changed by azole fungicide. Six metabolic pathways which are affected by fungicides were selected and showed similar patterns regardless of the type of azole fungicide used. As a result, azole fungicide induces the defense mechanisms of plants and affects both primary and secondary metabolism.

Developing multifunctional crops by engineering Brassicaceae glucosinolate pathways

Glucosinolates (GSLs), found mainly in species of the Brassicaceae family, are one of the most well-studied classes of secondary metabolites. Produced by the action of myrosinase on GSLs, GSL-derived hydrolysis products (GHPs) primarily defend against biotic stress in planta. They also significantly affect the quality of crop products, with a subset of GHPs contributing unique food flavors and multiple therapeutic benefits or causing disagreeable food odors and health risks. Here, we explore the potential of these bioactive functions, which could be exploited for future sustainable agriculture. We first summarize our accumulated understanding of GSL diversity and distribution across representative Brassicaceae species. We then systematically discuss and evaluate the potential of exploited and unutilized genes involved in GSL biosynthesis, transport, and hydrolysis as candidate GSL engineering targets. Benefiting from available information on GSL and GHP functions, we explore options for multifunctional Brassicaceae crop ideotypes to meet future demand for food diversification and sustainable crop production. An integrated roadmap is subsequently proposed to guide ideotype development, in which maximization of beneficial effects and minimization of detrimental effects of GHPs could be combined and associated with various end uses. Based on several use-case examples, we discuss advantages and limitations of available biotechnological approaches that may contribute to effective deployment and could provide novel insights for optimization of future GSL engineering.

Genus Brassica By-Products Revalorization with Green Technologies to Fortify Innovative Foods: A Scoping Review

Food losses and waste reduction are a worldwide challenge involving governments, researchers, and food industries. Therefore, by-product revalorization and the use of key extracted biocompounds to fortify innovative foods seems an interesting challenge to afford. The aim of this review is to evaluate and elucidate the scientific evidence on the use of green technologies to extract bioactive compounds from Brassica by-products with potential application in developing new foods. Scopus was used to search for indexed studies in JCR-ISI journals, while books, reviews, and non-indexed JCR journals were excluded. Broccoli, kale, cauliflower, cabbage, mustard, and radish, among others, have been deeply reviewed. Ultrasound and microwave-assisted extraction have been mostly used, but there are relevant studies using enzymes, supercritical fluids, ultrafiltration, or pressurized liquids that report a great extraction effectiveness and efficiency. However, predictive models must be developed to optimize the extraction procedures. Extracted biocompounds can be used, free or encapsulated, to develop, reformulate, and/or fortify new foods as a good tool to enhance healthiness while preserving their quality (nutritional, functional, and sensory) and safety. In the age of recycling and energy saving, more studies must evaluate the efficiency of the processes, the cost, and the environmental impact leading to the production of new foods and the sustainable extraction of phytochemicals.

Hepatoprotective Effects of Radish (Raphanus sativus L.) on Acetaminophen-Induced Liver Damage via Inhibiting Oxidative Stress and Apoptosis

Alcohol and drug overdoses cause liver diseases such as cirrhosis, hepatitis, and liver cancer globally. In particular, an overdose of acetaminophen (APAP), which is generally used as an analgesic and antipyretic agent, is a major cause of acute hepatitis, and cases of APAP-induced liver damage are steadily increasing. Potential antioxidants may inhibit the generation of free radicals and prevent drug-induced liver damage. Among plant-derived natural materials, radishes (RJ) and turnips (RG) have anti-inflammatory, anticancer, and antioxidant properties due to the presence of functional ingredients, such as glucosinolate and isothiocyanate. Although various functions have been reported, in vivo studies on the antioxidant activity of radishes are insufficient. Therefore, we aim to evaluate the hepatoprotective effects of RG and RJ in APAP-induced liver-damaged mice. RG and RJ extracts markedly improved the histological status, such as inflammation and infiltration, of mice liver tissue, significantly decreased the levels of alanine transaminase, aspartate aminotransferase, and malondialdehyde, and significantly increased the levels of glutathione, superoxide dismutase and catalase in the APAP-induced liver-damaged mice. In addition, RG and RJ extracts significantly increased the expression of Nrf-2 and HO-1, which are antioxidative-related factors, and regulated the BAX and BCL-2, thereby showing anti-apoptosis activity. These results indicated that RG and RJ extracts protected mice against acute liver injury, attributed to a reduction in both oxidative stress and apoptosis. These findings have clinical implications for the use of RG and RJ extracts as potential natural candidates for developing hepatoprotective agents.

Identification and analysis of major flavor compounds in radish taproots by widely targeted metabolomics

Radish (Raphanus sativus L.) is an important Brassicaceous vegetable crop that is cultivated worldwide. The taste of radish can be described as pungent, sweet, and crisp. At present, the metabolic characteristics leading to differences in radish taste remain unclear, due to the lack of large-scale detection and identification of radish metabolites. In this study, UPLC-MS/MS-based targeted metabolome analysis was performed on the taproots of eight radish landraces. We identified a total of 938 metabolites, and each landrace exhibited a specific metabolic profile, making it unique in flavor and quality. Our results show that taste differences among the taproots of different radish landraces can be explained by changes in composition and abundance of glucosinolates, polyphenols, carbohydrates, organic acids, amino acids, vitamins, and lipids. This study reveals the potential metabolic causes of variation in the taste and flavor of radish taproots.

A Comparative Transcriptome and Metabolome Combined Analysis Reveals the Key Genes and Their Regulatory Model Responsible for Glucoraphasatin Accumulation in Radish Fleshy Taproots

Radish (Raphanus sativus L.) is rich in specific glucosinolates (GSLs), which benefit human health and special flavor formation. Although the basic GSLs metabolic pathway in Brassicaceae plants is clear, the regulating mechanism for specific glucosinolates content in radish fleshy taproots is not well understood. In this study, we discovered that there was a significant difference in the GSLs profiles and the content of various GSLs components. Glucoraphasatin (GRH) is the most predominant GSL in radish taproots of different genotypes as assessed by HPLC analysis. Further, we compared the taproot transcriptomes of three radish genotypes with high and low GSLs content by employing RNA-seq. Totally, we identified forty-one differentially expressed genes related to GSLs metabolism. Among them, thirteen genes (RsBCAT4, RsIPMDH1, RsMAM1a, RsMAM1b, RsCYP79F1, RsGSTF9, RsGGP1, RsSUR1, RsUGT74C1, RsST5b, RsAPK1, RsGSL-OH, and RsMYB28) were significantly higher co-expressed in the high content genotypes than in low content genotype. Notably, correlation analysis indicated that the expression level of RsMYB28, as an R2R3 transcription factor directly regulating aliphatic glucosinolate biosynthesis, was positively correlated with the GRH content. Co-expression network showed that RsMYB28 probably positively regulated the expression of the above genes, particularly RsSUR1, and consequently the synthesis of GRH. Moreover, the molecular mechanism of the accumulation of this 4-carbon (4C) GSL in radish taproots was explored. This study provides new perspectives on the GSLs accumulation mechanism and genetic improvements in radish taproots.

Insights into glucosinolate accumulation and metabolic pathways in Isatis indigotica Fort

BACKGROUND

Glucosinolates (GSLs) play important roles in defending against exogenous damage and regulating physiological activities in plants. However, GSL accumulation patterns and molecular regulation mechanisms are largely unknown in Isatis indigotica Fort.

RESULTS

Ten GSLs were identified in I. indigotica, and the dominant GSLs were epiprogoitrin (EPI) and indole-3-methyl GSL (I3M), followed by progoitrin (PRO) and gluconapin (GNA). The total GSL content was highest (over 20 μmol/g) in reproductive organs, lowest (less than 1.0 μmol/g) in mature organs, and medium in fresh leaves (2.6 μmol/g) and stems (1.5 μmol/g). In the seed germination process, the total GSL content decreased from 27.2 μmol/g (of seeds) to 2.7 μmol/g (on the 120th day) and then increased to 4.0 μmol/g (180th day). However, the content of indole GSL increased rapidly in the first week after germination and fluctuated between 1.13 μmol/g (28th day) and 2.82 μmol/g (150th day). Under the different elicitor treatments, the total GSL content increased significantly, ranging from 2.9-fold (mechanical damage, 3 h) to 10.7-fold (MeJA, 6 h). Moreover, 132 genes were involved in GSL metabolic pathways. Among them, no homologs of AtCYP79F2 and AtMAM3 were identified, leading to a distinctive GSL profile in I. indigotica. Furthermore, most genes involved in the GSL metabolic pathway were derived from tandem duplication, followed by dispersed duplication and segmental duplication. Purifying selection was observed, although some genes underwent relaxed selection. In addition, three tandem-arrayed GSL-OH genes showed different expression patterns, suggesting possible subfunctionalization during evolution.

CONCLUSIONS

Ten different GSLs with their accumulation patterns and 132 genes involved in the GSL metabolic pathway were explored, which laid a foundation for the study of GSL metabolism and regulatory mechanisms in I. indigotica.

Seasonal Effects of Glucosinolate and Sugar Content Determine the Pungency of Small-Type (Altari) Radishes (Raphanus sativus L.)

Kimchi made from small-type (Altari) radishes grown in late spring is more pungent than that made from autumn-grown Altari radishes, which poses a major challenge in the kimchi industry. The mechanism through which the pungency of Altari radish changes seasonally has not been intensively investigated. In this study, three small-type radish cultivars with different pungency levels were cultivated in spring and autumn to identify the factors affecting the seasonal-dependent pungency of small-type radishes. The contents of pungency-related metabolite glucoraphasatin and other polar metabolites were analyzed. Although a previous study reported that the glucoraphasatin concentration affects the pungency of radish, in the current study, the concentration of neither glucoraphasatin nor its hydrolysis product (raphasatin) could fully explain the change in the pungency associated with radish cultivars grown in the two seasons. The change in the pungency of radish by season may be explained by the ratio of raphasatin content to total sweetness of sugars. In addition, the polar metabolites that differ with season were analyzed to identify seasonal biomarkers and understand the seasonal changed physio-biochemistry.

Glucosinolate Profiles in Different Organs of 111 Radish Accessions and Candidate Genes Involved in Converting Glucobrassicin to 4-Hydroxyglucobrassicin

Glucosinolate (GSL) not only has highly physiological function for plants but also has considerable human interest. We analyzed the GSL compositions and levels in four organs of 111 radish accessions. Seven major GSLs were detected (approximately 5-245 μmol g^-1 DW), among which 4-(methylsulfinyl)but-3-enyl GSL and 4-methylsulfanyl-3-butenyl GSL were the dominant GSLs. GSL levels varied substantially among species and groups, and some genotypes/groups with special GSL profiles were identified. The total GSL level was higher in seeds than in sprouts, taproots, and leaves. Additionally, a correlation analysis revealed that seed 4-(methylsulfinyl)but-3-enyl GSL levels were highly correlated with sprout GSL levels. Moreover, a candidate gene (RsCYP81F2.3) encoding an enzyme that catalyzes the conversion of indol-3-ylmethyl GSL to 4-hydroxyindol-3-ylmethyl GSL was identified based on the detection and analysis of three radish accessions with relatively high indol-3-ylmethyl GSL, low 4-hydroxyindol-3-ylmethyl GSL, and 4-methoxyindol-3-ylmethyl GSL levels in their seeds. Our results provide some insights for finding materials and genes relevant for breeding new varieties with ideal GSL compositions and levels.

Phytonutrients and Metabolism Changes in Topped Radish Root and Its Detached Leaves during 1 °C Cold Postharvest Storage

Glucosinolates, lipid-soluble vitamins E and K contents, primary metabolites and plant hormones were analyzed from topped radish root and detached leaf during storage at 1 °C. The topped root was analyzed at 0, 5, 15, 30, and 90 days after storage while the detached leaf was analyzed at 0, 5, 15, 30, and 45 days in an airtight storage atmosphere environment. The results showed that aliphatic glucosinolates were gradually decreased in leaf but not in root. There was a highly significant correlation between tryptophan and 4-methoxyindoleglucobrassicin in both tissues (r = 0.922, n = 10). There was no significant difference in vitamins E and K in leaf and root during storage. Plant hormones partially explained the significantly changed metabolites by tissue and time, which were identified during cold storage. Phenylalanine, lysine, tryptophan, and myo-inositol were the most important biomarkers that explained the difference in leaf and root tissue during cold storage. The most different metabolism between leaf and root tissue was starch and sucrose metabolism. Therefore, different postharvest technology or regimes should be applied to these tissues.

Analysis of Phenotypic Characteristics and Sucrose Metabolism in the Roots of Raphanus sativus L

The taproot of radish (Raphanus sativus L.) is an important sink organ; it is morphologically diverse and contains large amounts of secondary metabolites. Sucrose metabolism is believed to be important in the development of sink organs. We measured the amounts of glucose, fructose, and sucrose in the roots of sixty three radish accessions and analyzed the association between the sugar content and the root phenotype. Fructose content correlated with the root color and length characteristics, glucose was the most abundant sugar in the roots, and the sucrose content was very low, compared to that of the hexoses in most of the accessions. Expression analysis of the genes involved in sucrose metabolism, transportation, starch synthesis, and cell wall synthesis was performed through RNA sequencing. The genes encoding sucrose synthases (SUSY) and the enzymes involved in the synthesis of cellulose were highly expressed, indicating that SUSY is involved in cell wall synthesis in radish roots. The positive correlation coefficient (R) between the sucrose content and the expression of cell wall invertase and sugar transporter proteins suggest that hexose accumulation could occur through the apoplastic pathway in radish roots. A positive R score was also obtained when comparing the expression of genes encoding SUSY and fructokinase (FK), suggesting that the fructose produced by SUSY is mostly phosphorylated by FK. In addition, we concluded that sucrose was the most metabolized sugar in radish roots.

Interactions between Brassica Biofumigants and Soil Microbiota: Causes and Impacts

Biofumigation is used to control soil-borne plant diseases, and it has paramount importance to reduce the cost of chemical fumigants. Information about the field control efficacies and impacts of Brassica-based biofumigation (BBF) on soil bacterial and fungal microbiota is scattered in the literature. Therefore, this review summarizes and discusses the nature and the underlying causes of soil bacterial and fungal community dynamics in response to BBF. In addition, the major factors influencing the interaction between a biofumigant and soil microbiota are discussed. The pros and cons of BBF to soil microbiota and the subsequent impacts on sustainable farming practices are also highlighted.

Metabolomic insight into the profile, in vitro bioaccessibility and bioactive properties of polyphenols and glucosinolates from four Brassicaceae microgreens

In this study, four Brassicaceae microgreens species, namely kale, red cabbage, kohlrabi, and radish, were evaluated for their phytochemical compositions using spectrophotometric assays and untargeted metabolomics before and after in vitro gastrointestinal digestion. According to the in vitro spectrophotometric results, significant amounts of phenolics could be detected in each studied species, thus supporting the total antioxidant capacities recorded. Overall, metabolomics allowed annotating a total of 470 phytochemicals across the four Brassicaceae microgreens, either fresh or digested. Among polyphenols, flavonoids were the most represented class (180 compounds, including anthocyanins, flavones, flavonols, and other flavonoids), followed by phenolic acids (68 compounds, mainly hydroxycinnamic and hydroxybenzoic acids), non-flavonoid or phenolic acid-based structures (i.e., alkyl- and alkylmethoxy-phenols and tyrosol derivatives), and lignans. Also, 22 glucosinolates were annotated, including gluconapin glucoraphanin, glucobrassicin, and 4-hydroxyglucobrassicin. Noteworthy, significant differences could be observed in terms of bioaccessibility as a function of the phenolic class and the species considered. Overall, lignans exhibited the highest bioaccessibility values (14%), followed by tyrosol derivatives and flavonoids (on average, 9% and 8%, respectively). However, differences could be evidenced as a function of the species, with red cabbage having comparatively lower bioaccessibility values irrespective of the chemical class of bioactive considered. Similarly, bioaccessibility of glucosinolates significantly differed across species, ranging from 2% in kale to 43% in kohlrabi microgreens.

Effect of neonicotinoid dinotefuran on root exudates of Brassica rapa var. chinensis

Root exudates are released by plant roots and are important carrier substances for material exchange and information transmission among plants and the rhizosphere. In the present study, the effect of dinotefuran on root exudates of Chinese cabbage (Brassica rapa var. chinensis) was investigated. The physiological activities revealed that dinotefuran uptake caused oxidative stress in vegetable tissues even at low dinotefuran exposure levels. The metabolic profile of plant root exudates acquired by LC-QTOF/MS was clearly changed by dinotefuran, where the numbers of both up- and down-regulated MS peaks increased with increasing dinotefuran concentration. Under dinotefuran stress, some osmotic adjustment substances (proline and betaine) and defence-related metabolites (spermidine, phenylalanine and some phenolic acids) were significantly upregulated, which may help plants adapt to adverse environmental conditions. Specifically, the contents of some phenylalanine-derived secondary metabolites increased with increasing dinotefuran concentration, which may increase the external detoxification ability of plants. Moreover, respiration metabolism was significantly affected, where some intermediates in the TCA cycle (succinic acid and malic acid) were upregulated with low-level dinotefuran exposure; however, anaerobic respiration products (lactic acid and 3-phenyllactic acid) were accumulated at high exposure levels. In addition, the release of glucosinolates was significantly inhibited in both dinotefuran treatment groups.

Development of HPLC Method for Quantification of Sinigrin from Raphanus sativus Roots and Evaluation of Its Anticancer Potential

Sinigrin, a precursor of allyl isothiocyanate, present in the Raphanus sativus exhibits diverse biological activities, and has an immense role against cancer proliferation. Therefore, the objective of this study was to quantify the sinigrin in the R. sativus roots using developed and validated RP-HPLC method and further evaluated its’ anticancer activity. To achieve the objective, the roots of R. sativus were lyophilized to obtain a stable powder, which were extracted and passed through an ion-exchange column to obtain sinigrin-rich fraction. The RP-HPLC method using C18 analytical column was used for chromatographic separation and quantification of sinigrin in the prepared fraction, which was attained using the mobile phase consisting of 20 mM tetrabutylammonium: acetonitrile (80:20%, v/v at pH 7.0) at a flow rate of 0.5 mL/min. The chromatographic peak for sinigrin was showed at 3.592 min for pure sinigrin, where a good linearity was achieved within the concentration range of 50 to 800 µg/mL (R² > 0.99), with an excellent accuracy (−1.37% and −1.29%) and precision (1.43% and 0.94%), for intra and inter-day, respectively. Finally, the MTT assay was performed for the sinigrin-rich fraction using three different human cancer cell lines, viz. prostate cancer (DU-145), colon adenocarcinoma (HCT-15), and melanoma (A-375). The cell-based assays were extended to conduct apoptotic and caspase-3 activities, to determine the mechanism of action of sinigrin in the treatment of cancer. MTT assay showed IC₅₀ values of 15.88, 21.42, and 24.58 µg/mL for DU-145, HCT-15, and A-375 cell lines, respectively. Increased cellular apoptosis and caspase-3 expression were observed with sinigrin-rich fraction, indicating significant increase in overexpression of caspase-3 in DU-145 cells. In conclusion, a simple, sensitive, fast, and accurate RP-HPLC method was developed for the estimation of sinigrin in the prepared fraction. The data observed here indicate that sinigrin can be beneficial in treating prostate cancer possibly by inducing apoptosis.

Glucosinolates: Natural Occurrence, Biosynthesis, Accessibility, Isolation, Structures, and Biological Activities

Glucosinolates (GSLs) are secondary plant metabolites abundantly found in plant order Brassicales. GSLs are constituted by an S-β-d-glucopyrano unit anomerically connected to O-sulfated (Z)-thiohydroximate moiety. The side-chain of the O-sulfate thiohydroximate moiety, which is derived from a different amino acid, contributes to the diversity of natural GSL, with more than 130 structures identified and validated to this day. Both the structural diversity of GSL and their biological implication in plants have been biochemically studied. Although chemical syntheses of GSL have been devised to give access to these secondary metabolites, direct extraction from biomass remains the conventional method to isolate natural GSL. While intact GSLs are biologically inactive, various products, including isothiocyanates, nitriles, epithionitriles, and cyanides obtained through their hydrolysis of GSLs, exhibit many different biological activities, among which several therapeutic benefits have been suggested. This article reviews natural occurrence, accessibility via chemical, synthetic biochemical pathways of GSL, and the current methodology of extraction, purification, and characterization. Structural information, including the most recent classification of GSL, and their stability and storage conditions will also be discussed. The biological perspective will also be explored to demonstrate the importance of these prominent metabolites.

Induction of Glucoraphasatin Biosynthesis Genes by MYB29 in Radish (Raphanus sativus L.) Roots

Glucoraphasatin (GRH) is a specific aliphatic glucosinolate (GSL) that is only abundant in radish (Raphanus sativus L.). The gene expression regulating GRH biosynthesis in radish is still poorly understood. We employed a total of 59 radish accessions to analyze GSL profiles and showed that GRH was specific and predominant among the aliphatic GSLs in radish roots. We selected five accessions roots with high, moderate and low GSL biosynthesis, respectively, to conduct a comparative transcriptome analysis and the qRT-PCR of the biosynthesis genes for aliphatic GSLs. In this study, among all the accessions tested, roots with the accession RA157-74 had a high GRH content and showed a significant expression of the aliphatic GSL biosynthesis genes. We defined the genes involved in the GRH biosynthesis process and found that they were regulated by a transcription factor (RSG00789) at the MYB29 locus in radish roots. We found 13 aliphatic GSL biosynthesis genes regulated by the RSG00789 gene in the GRH biosynthesis pathway.

Profiling of Individual Desulfo-Glucosinolate Content in Cabbage Head (Brassica oleracea var. capitata) Germplasm

Individual glucosinolates (GSLs) were assessed to select cabbage genotypes for a potential breeding program. One hundred forty-six cabbage genotypes from different origins were grown in an open field from March to June 2019; the cabbage heads were used for GSL analyses. Seven aliphatics [glucoiberin (GIB), progoitrin (PRO), epi-progoitrin (EPI), sinigrin (SIN), glucoraphanin (GRA), glucoerucin (GER) and gluconapin (GNA)], one aromatic [gluconasturtiin (GNS)] and four indolyl GSLs [glucobrassicin (GBS), 4-hydroxyglucobrassicin (4HGBS), 4-methoxyglucobrassicin (4MGBS), neoglucobrassicin (NGBS)] were found this study. Significant variation was observed in the individual GSL content and in each class of GSLs among the cabbage genotypes. Aliphatic GSLs were predominant (58.5%) among the total GSLs, followed by indolyl GSL (40.7%) and aromatic GSLs (0.8%), showing 46.4, 51.2 and 137.8% coefficients of variation, respectively. GIB, GBS and NGBS were the most common GSLs found in all genotypes. GBS was the most dominant GSL, with an average value of 3.91 µmol g⁻¹ (0.79 to 13.14 µmol g⁻¹). SIN, GIB, PRO and GRA were the other major GSLs, showing average values of 3.45, 1.50, 0.77 and 0.62 µmol g⁻¹, respectively. The genotypes with relatively high contents of GBS, SIN, GIB and GRA warrant detailed studies for future breeding programs since the hydrolysis products of these GSLs have several anti-cancer properties.

Functional Ingredients From Brassicaceae Species: Overview and Perspectives

Brassicaceae vegetables are important crops consumed worldwide due to their unique flavor, and for their broadly recognized functional properties, which are directly related to their phytochemical composition. Isothiocyanates (ITC) are the most characteristic compounds, considered responsible for their pungent taste. Besides ITC, these vegetables are also rich in carotenoids, phenolics, minerals, and vitamins. Consequently, Brassica's phytochemical profile makes them an ideal natural source for improving the nutritional quality of manufactured foods. In this sense, the inclusion of functional ingredients into food matrices are of growing interest. In the present work, Brassicaceae ingredients, functionality, and future perspectives are reviewed.

Simultaneous Quantification of 22 Glucosinolates in 12 Brassicaceae Vegetables by Hydrophilic Interaction Chromatography-Tandem Mass Spectrometry

Glucosinolates, which are unique to Brassicaceae vegetables, have diverse biological activities, including antimicrobial, antioxidant, and anticancer actions. In this study, we applied hydrophilic interaction chromatography-tandem mass spectrometry (HILIC-MS/MS) to the simultaneous quantification of 22 glucosinolates in 12 Brassicaceae vegetables, including pak choi, choy sum, Chinese cabbage, cauliflower, cabbage, broccoli, Kai Lan, Brussels sprouts, rocket salad, daikon radish, red cherry radish, and watercress. Significant differences in concentration and composition of glucosinolates were observed among these vegetables. Cabbage had the highest level of total glucosinolates (μg/g dry weight: 19 551.2 ± 1317.7), whereas Kai Lan had the lowest level (7611.3 ± 868.4). Aliphatic and indole glucosinolates were the major components in the 12 vegetables ranging from 76 to 100%, except watercress (37%). On the basis of the content of glucosinolates, the 12 vegetables were well distinguishable and classified according to their morphological taxonomy. This study presents a HILIC-MS/MS approach for quantification of glucosinolates, and demonstrates the potential of glucosinolate profiles for Brassicaceae species identification.

MYB1 transcription factor is a candidate responsible for red root skin in radish (Raphanus sativus L.)

Root skin color is one of the economically important traits in radish (Raphanus sativus), and the pigmentation in red skin varieties is largely attributable to anthocyanin accumulation. Pelargonidin was found as a major anthocyanin pigment accumulated in the sub-epidermal layer of red radish roots. In the 20 F₂ population generated from the F₁ with red root skins, root skins with red and white colors segregated in a 3:1 ratio. Additionally, a test cross between a red F₃ individual and a white skin individual gave rise to 1:1 segregation of red and white, indicating that the root skin color of radish is determined by a single locus and red color is dominant over white. We performed association mapping for root skin color using SNPs obtained from RNA-seq analysis. Segregation analysis on the 152 F₃ test-cross population revealed an RsMyb1 transcription factor as a candidate gene to determine root skin color. A PCR marker based on the polymorphism within 2 kb of RsMyb1 was developed and tested on 12 and 152 individuals from F₂ and F₃ test cross populations, respectively, and red and white root skin colors were completely distinguished corresponding to the genotypes. Expression levels of RsMyb1 in red or purple root cultivars were significantly higher than in white root cultivars. These findings suggest that RsMyb1 is a crucial determinant for anthocyanin biosynthesis in radish roots, and the molecular marker developed in this study will be useful for marker-assisted selection for red skin individuals at early seedling stages.

Insights into the species-specific metabolic engineering of glucosinolates in radish (Raphanus sativus L.) based on comparative genomic analysis

Glucosinolates (GSLs) and their hydrolysis products present in Brassicales play important roles in plants against herbivores and pathogens as well as in the protection of human health. To elucidate the molecular mechanisms underlying the formation of species-specific GSLs and their hydrolysed products in Raphanus sativus L., we performed a comparative genomics analysis between R. sativus and Arabidopsis thaliana. In total, 144 GSL metabolism genes were identified, and most of these GSL genes have expanded through whole-genome and tandem duplication in R. sativus. Crucially, the differential expression of FMOGS-OX2 in the root and silique correlates with the differential distribution of major aliphatic GSL components in these organs. Moreover, MYB118 expression specifically in the silique suggests that aliphatic GSL accumulation occurs predominantly in seeds. Furthermore, the absence of the expression of a putative non-functional epithiospecifier (ESP) gene in any tissue and the nitrile-specifier (NSP) gene in roots facilitates the accumulation of distinctive beneficial isothiocyanates in R. sativus. Elucidating the evolution of the GSL metabolic pathway in R. sativus is important for fully understanding GSL metabolic engineering and the precise genetic improvement of GSL components and their catabolites in R. sativus and other Brassicaceae crops.

The mechanism of deterioration of the glucosinolate-myrosynase system in radish roots during cold storage after harvest

The hydrolysis of glucosinolates (GSLs) by myrosinase yields varieties of degradation products including isothiocyanates (ITCs). This process is controlled by the glucosinolate-myrosinase (G-M) system. The major ITCs in radish roots are raphasatin and sulforaphene (SFE), and the levels of these compounds decrease during storage after harvest. We investigated the G-M system to understand the mechanism behind the decrease in the ITCs in radish roots. Six varieties of radish roots were stored for 8weeks at 0-1.5°C. The concentrations of GSLs (glucoraphasatin and glucoraphenin) were maintained at harvest levels without significant changes during the storage period. However, SFE concentration and myrosinase activity remarkably decreased for 8weeks. Pearson correlation analysis between ITCs, GSLs, and myrosinase activity showed that a decrease of SFE during storage had a positive correlation with a decrease in myrosinase activity, which resulted from a decrease of ascorbic acid but also a decrease of myrosinase activity-related gene expressions.