Accumulation Of Glucosinolates Research Articles

Metabolite profiles of glucosinolates in cabbage varieties (Brassica oleracea var. capitata) by season, color, and tissue position

Glucosinolates (GSLs) are sulfur-containing anionic secondary metabolites that are precursors of biologically active compounds, such as isothiocyanates, in Brassicaceae. The GSLs found in 10 cultivars of cabbage (Brassica oleracea var. capitata) popularly cultivated in Korea and China were identified and quantified. Three GSL classes (6 aliphatic, 1 aromatic, and 3 indolyl) were identified and quantified using high-performance liquid chromatography mass spectrometry (HPLC-MS) and HPLC. The concentration of these GSLs varied by season (spring- and fall-sown), leaf position (inside and outside), and cabbage color (green and red). The average total amounts of GSLs in the inner and outer sections of green and red cabbages ranged from 8.55–13.5 μmol∙g−1 dry weight. The spring-sown cabbages contained significantly higher GSL concentration (2.3–4.3 times higher) compared to their fall-sown counterparts. The inner sections of cabbages contained 1.1- to 1.8-fold greater GSL concentrations than the outer sections. These results indicate that an increase in temperature induces GSL accumulation in both green and red cabbages. The green cabbage cultivars contained significantly higher concentration of GSLs synthesized from homo-methionine, whereas the red cabbage cultivars had greater amounts of GSLs synthesized from dihomo-methionine, which suggests that the activities of enzymes involved in the elongation of homo-methionine are greater in red cabbages. The fall-sown red cabbages also contained 2- to 3-fold higher contents of GSLs synthesized from tryptophan compared to the spring-sown cabbages. In conclusion, the color of cabbage, tissue position of cabbage, temperature, and rainfall were all significantly correlated with the amount of GSL accumulation in cabbages.

Arbuscular mycorrhizal fungi affect glucosinolate and mineral element composition in leaves of Moringa oleifera

Moringa is a mycorrhizal crop cultivated in the tropics and subtropics and appreciated for its nutritive and health-promoting value. As well as improving plant mineral nutrition, arbuscular mycorrhizal fungi (AMF) can affect plant synthesis of compounds bioactive against chronic diseases in humans. Rhizophagus intraradices and Funneliformis mosseae were used in a full factorial experiment to investigate the impact of AMF on the accumulation of glucosinolates, flavonoids, phenolic acids, carotenoids, and mineral elements in moringa leaves. Levels of glucosinolates were enhanced, flavonoids and phenolic acids were not affected, levels of carotenoids (including provitamin A) were species-specifically reduced, and mineral elements were affected differently, with only Cu and Zn being increased by the AMF. This study presents novel results on AMF effects on glucosinolates in leaves and supports conclusions that the impacts of these fungi on microelement concentrations in edible plants are species dependent. The nonspecific positive effects on glucosinolates and the species-specific negative effects on carotenoids encourage research on other AMF species to achieve general benefits on bioactive compounds in moringa.

Variation of Glucosinolate Accumulation and Gene Expression of Transcription Factors at Different Stages of Chinese Cabbage Seedlings under Light and Dark Conditions

Chinese cabbage is one of the most important leafy vegetables widely used in East Asian cuisines. The glucosinolate (GSL) accumulation and transcript levels of 7 transcription factors (Dof1.1, IQD1-1, MYB28, MYB29, MYB34, MYB51, and MYB122, and their isoforms) involved in the biosynthesis of aliphatic and indolic glucosinolates (GSLs) were analyzed at different stages of Chinese cabbage (Brassica rapa ssp. pekinensis) seedlings under light and dark conditions using high performance liquid chromatography and quantitative real time PCR. During seedling development, transcription of almost all transcription factors under light conditions was higher expressed than under dark conditions. Five aliphatic GSLs (progoitrin, sinigrin, glucoalyssin, gluconapin, and glucobrassicanapin) and four indolic GSLs (4-hydroxyglucobrassicin, glucobrassicin, 4-methoxyglucobrassicin, and neoglucobrasscin) were detected. Total GSL contents under light conditions 6, 8, and 10 days after sowing (DAS) were 3.2-, 3.9-, and 6.9-fold higher, respectively than those of dark conditions. Interestingly, total GSL contents 2 {85.4 micromol/g dry weight (DW)} to 10 (7.74 micromol/g DW) DAS under dark conditions were gradually decreased. In this study, our results suggest that light affects the levels of GSL in Chinese cabbage seedlings. These results could be useful for obtaining cabbage varieties rich in GSLs.

Identification and Quantification of Glucosinolates in Rapeseed (Brassica napus L.) Sprouts Cultivated under Dark and Light Conditions

BACKGROUND: This study was performed for the identification and quantification of glucosinolate (GSL) contents in seven varieties of rapeseed (Brassica napus L.) sprouts cultivated under dark and light conditions. METHODS AND RESULTS: Crude glucosinolates (GSLs) were desulfated by treating with aryl sulfatase and purified using diethylaminoethyl sepharose (DEAE) anion exchange column. Individual GSLs were quantified using high-performance liquid chromatography (HPLC) with electrospray ionization-tandem mass spectrometry (ESI-MS/MS). Eleven GSLs including six aliphatic (progoitrin, sinigrin, glucoalyssin, gluconapoleiferin, gluconapin, and glucobrassicanapin), four indolyl (4-hydroxyglucobrassicin, glucobrassicin, 4-methoxyglucobrassicin, and neoglucobrassicin) and one aromatic (gluconasturtiin) were identified based on the fragmentation patterns of MS spectrum. Aliphatic GSLs were noted as the predominant group with average 85.2% of the total contents. The most abundant GSLs were progoitrin which was ranged at dry weight (DW). The highest total GSL amounts were documented in 'Hanra' ( DW) under light condition and 'Mokpo No. 68' ( DW) in dark condition, whereas the lowest was in 'Tamra' (30.13 and DW) in both conditions. The sum of aliphatic GSLs attributed > 80% in all varieties, except 'Tamra' (67.7% and 64.9% in dark and light conditions, respectively) in the total GSL accumulation. Indolyl GSLs were ranged DW, accounted 2.78-33.6% of the total GSLs in rapeseed varieties. CONCLUSION(S): These results provide valuable information regarding potential beneficial GSL contents individually. This study attempts to contribute to knowledge of the nutritional properties of the different varieties of rapeseed plants. These results may be useful for the evaluation of dietary information.

Topsoil drying combined with increased sulfur supply leads to enhanced aliphatic glucosinolates in Brassica juncea leaves and roots

The decrease of water availability is leading to an urgent demand to reduce the plants’ water supply. This study evaluates the effect of topsoil drying, combined with varying sulfur (S) supply on glucosinolates in Brassica juncea in order to reveal whether a partial root drying may already lead to a drought-induced glucosinolate increase promoted by an enhanced S supply. Without decreasing biomass, topsoil drying initiated an increase in aliphatic glucosinolates in leaves and in topsoil dried roots supported by increased S supply. Simultaneously, abscisic acid was determined, particularly in dehydrated roots, associated with an increased abscisic acid concentration in leaves under topsoil drying. This indicates that the dehydrated roots were the direct interface for the plants’ stress response and that the drought-induced accumulation of aliphatic glucosinolates is related to abscisic acid formation. Indole and aromatic glucosinolates decreased, suggesting that these glucosinolates are less involved in the plants’ response to drought.

Jasmonic acid and glucose synergistically modulate the accumulation of glucosinolates in Arabidopsis thaliana.

The interplay of plant hormones and glucose (Glu) in regulating glucosinolate accumulation in Arabidopsis thaliana was investigated in this study. Glucose-induced glucosinolate biosynthesis was enhanced significantly by the addition of jasmonic acid (JA), whereas the synergistic effect of salicylic acid (SA) and Glu was less obvious. The enhanced glucosinolate accumulation is associated with elevated expression of genes in glucosinolate biosynthetic pathway, as well as the transcription factors involved in their regulation, such as MYB28, MYB29, MYB34, and MYB122. The induction of indolic and aliphatic glucosinolates after treatment with JA and Glu in JA-insensitive mutants, coi1, jar1, and jin1, was compromised. Moreover, the effect of JA and Glu on glucosinolate contents was dramatically reduced in Glu-insensitive mutants, rgs1-2 and abi5-7. These results indicate a crosstalk between JA and Glu signalling in the regulation of glucosinolate biosynthesis. JA signalling, RGS1 (the putative membrane receptor of Glu signalling), and ABI5, are involved in the synergistic effect of JA and Glu on glucosinolate accumulation.

Verticillium suppression is associated with the glucosinolate composition of Arabidopsis thaliana leaves.

The soil-borne fungal pathogen Verticillium longisporum is able to penetrate the root of a number of plant species and spread systemically via the xylem. Fumigation of Verticillium contaminated soil with Brassica green manure is used as an environmentally friendly method for crop protection. Here we present a study focused on the potential role of glucosinolates and their breakdown products of the model plant Arabidopsis thaliana in suppressing growth of V. longisporum. For this purpose we analysed the glucosinolate composition of the leaves and roots of a set of 19 key accessions of A. thaliana. The effect of volatile glucosinolate hydrolysis products on the in vitro growth of the pathogen was tested by exposing the fungus to hydrated lyophilized plant tissue. Volatiles released from leaf tissue were more effective than from root tissue in suppressing mycelial growth of V. longisporum. The accessions varied in their efficacy, with the most effective suppressing mycelial growth by 90%. An analysis of glucosinolate profiles and their enzymatic degradation products revealed a correlation between fungal growth inhibition and the concentration of alkenyl glucosinolates, particularly 2-propenyl (2Prop) glucosinolate, respectively its hydrolysis products. Exposure of the fungus to purified 2Prop glucosinolate revealed that its suppressive activity was correlated with its concentration. Spiking of 2Prop glucosinolate to leaf material of one of the least effective A. thaliana accessions led to fungal growth suppression. It is suggested that much of the inhibitory effect observed for the tested accessions can be explained by the accumulation of 2Prop glucosinolate.

Peculiar properties of glucosinolate accumulation in the Brassicaceae family

The total content and the composition of the constituents of glucosinolates were analyzed in 51 samples of 6 species of 5 genera of the Brassicaceae family. The twenty-one component of the profile of glucosinolates, including fifteen aliphatic glucosinolates, four insole glucosinolates, and two aromatic glucosinolates, were revealed. The wide potential of variability of the constituent composition of glucosinolates was found, which allows to use the cabbage plants to various purposes, such as a valuable foodstuff and for fumigation of soils. All studied samples of Sinapsis alba L. and six samples of Brassica juncea Czen, which possess a high (more than 40 I¼mol/g) concentration of sinalbin and sinigrin, correspondingly, are recommended for biofumigation. It was revealed that the glucosinolates of Brassica rapa L. contain 17 constituents. For the first time, samples of the variety that have an increased value of constituent composition of glucosinolates for balanced food of people were found. These varieties are recommended for use in breeding, including for medical purposes, and for the completion of assortment of cabbage vegetables.

Integration of Biosynthesis and Long-Distance Transport Establish Organ-Specific Glucosinolate Profiles in VegetativeArabidopsis

Although it is essential for plant survival to synthesize and transport defense compounds, little is known about the coordination of these processes. Here, we investigate the above- and belowground source-sink relationship of the defense compounds glucosinolates in vegetative Arabidopsis thaliana. In vivo feeding experiments demonstrate that the glucosinolate transporters1 and 2 (GTR1 and GTR2), which are essential for accumulation of glucosinolates in seeds, are likely to also be involved in bidirectional distribution of glucosinolates between the roots and rosettes, indicating phloem and xylem as their transport pathways. Grafting of wild-type, biosynthetic, and transport mutants show that both the rosette and roots are able to synthesize aliphatic and indole glucosinolates. While rosettes constitute the major source and storage site for short-chained aliphatic glucosinolates, long-chained aliphatic glucosinolates are synthesized both in roots and rosettes with roots as the major storage site. Our grafting experiments thus indicate that in vegetative Arabidopsis, GTR1 and GTR2 are involved in bidirectional long-distance transport of aliphatic but not indole glucosinolates. Our data further suggest that the distinct rosette and root glucosinolate profiles in Arabidopsis are shaped by long-distance transport and spatially separated biosynthesis, suggesting that integration of these processes is critical for plant fitness in complex natural environments.

Proteomic investigation of glucosinolate systematically changes in Arabidopsis Rosette leaves to exogenous methyl jasmonate

Defense responses of plants are activated not only in the wounded tissues but also in the remote parts of the plants. Two different methyl jasmonate (MeJA) treatments were conducted, i.e., MeJA solution spraying of entire rosettes leaves and pasting leaf surface with lanolin squares containing MeJA. Glucosinolate profiles in leaves were similar using the two methods of MeJA treatment except for indole glucosinolates. The glucosinolate profiles in local and systemic leaves showed that the accumulation of glucosinolates in systemic leaves were delayed comparing with those in local treated leaves. Comparative proteomics were used to investigate the molecular processes underlying the glucosinolate changes in response to local and systemic MeJA induction. A total of 83 unique proteins were detected as differentially expressed between the local and systemic leaves. Functional analysis showed that redirection of metabolism from growth to defense was differentially regulated in local and systemic MeJA induction. The higher contents of indole glucosinolates in systemic leaves might arise from the induction of a long-distance signal produced in local leaves as well as from JA synthesized in systemic leaves.

The Effects of Glucosinolates and Their Breakdown Products on Necrotrophic Fungi

Glucosinolates are a diverse class of S- and N-containing secondary metabolites that play a variety of roles in plant defense. In this study, we used Arabidopsis thaliana mutants that contain different amounts of glucosinolates and glucosinolate-breakdown products to study the effects of these phytochemicals on phytopathogenic fungi. We compared the fungus Botrytis cinerea, which infects a variety of hosts, with the Brassicaceae-specific fungus Alternaria brassicicola. B. cinerea isolates showed variable composition-dependent sensitivity to glucosinolates and their hydrolysis products, while A. brassicicola was more strongly affected by aliphatic glucosinolates and isothiocyanates as decomposition products. We also found that B. cinerea stimulates the accumulation of glucosinolates to a greater extent than A. brassicicola. In our work with A. brassicicola, we found that the type of glucosinolate-breakdown product is more important than the type of glucosinolate from which that product was derived, as demonstrated by the sensitivity of the Ler background and the sensitivity gained in Col-0 plants expressing epithiospecifier protein both of which accumulate simple nitrile and epithionitriles, but not isothiocyanates. Furthermore, in vivo, hydrolysis products of indole glucosinolates were found to be involved in defense against B. cinerea, but not in the host response to A. brassicicola. We suggest that the Brassicaceae-specialist A. brassicicola has adapted to the presence of indolic glucosinolates and can cope with their hydrolysis products. In contrast, some isolates of the generalist B. cinerea are more sensitive to these phytochemicals.

Novel bioresources for studies of Brassica oleracea: identification of a kale MYB transcription factor responsible for glucosinolate production

Plants belonging to the Brassicaceae family exhibit species-specific profiles of glucosinolates (GSLs), a class of defence compounds against pathogens and insects. GSLs also exhibit various human health-promoting properties. Among them, glucoraphanin (aliphatic 4-methylsulphinylbutyl GSL) has attracted the most attention because it hydrolyses to form a potent anticancer compound. Increased interest in developing commercial varieties of Brassicaceae crops with desirable GSL profiles has led to attempts to identify genes that are potentially valuable for controlling GSL biosynthesis. However, little attention has been focused on genes of kale (Brassica oleracea var. acephala). In this study, we established full-length kale cDNA libraries containing 59904 clones, which were used to generate an expressed sequence tag (EST) data set with 119204 entries. The EST data set clarified genes related to the GSL biosynthesis pathway in kale. We specifically focused on BoMYB29, a homolog of Arabidopsis MYB29/PMG2/HAG3, not only to characterize its function but also to demonstrate its usability as a biological resource. BoMYB29 overexpression in wild-type Arabidopsis enhanced the expression of aliphatic GSL biosynthetic genes and the accumulation of aliphatic GSLs. When expressed in the myb28myb29 mutant, which exhibited no detectable aliphatic GSLs, BoMYB29 restored the expression of biosynthetic genes and aliphatic GSL accumulation. Interestingly, the ratio of methylsulphinyl GSL content, including glucoraphanin, to that of methylthio GSLs was greatly increased, indicating the suitability of BoMYB29 as a regulator for increasing methylsulphinyl GSL content. Our results indicate that these biological resources can facilitate further identification of genes useful for modifications of GSL profiles and accumulation in kale.

MYB transcription factors regulate glucosinolate biosynthesis in different organs of Chinese cabbage (Brassica rapa ssp. pekinensis).

In this study, we investigated the expression of seven MYB transcription factors (a total of 17 genes that included Dof1.1, IQD1-1, MYB28, MYB29, MYB34, MYB51, and MYB122 and their isoforms) involved in aliphatic and indolic glucosinolate (GSL) biosynthesis and analyzed the aliphatic and indolic GSL content in different organs of Chinese cabbage (Brassica rapassp. Pekinensis). MYB28 and MYB29 expression in the stem was dramatically different when compared with the levels in the other organs. MYB34, MYB122, MYB51, Dof1.1, and IQD1-1 showed very low transcript levels among different organs. HPLC analysis showed that the glucosinolates (GSLs) consisted of five aliphatic GSLs (progoitrin, sinigrin, glucoalyssin, gluconapin, and glucobrassicanapin) and four indolic GSLs (4-hydroxyglucobrassicin, glucobrassicin, 4-methoxygluco-brassicin, and neoglucobrassicin). Aliphatic GSLs exhibited 63.3% of the total GSLs content, followed by aromatic GSL (19.0%), indolic GSLs (10%), and unknown GSLs (7.7%) in different organs of Chinese cabbage. The total GSL content of different parts (ranked in descending order) was as follows: seed > flower > young leaves > stem > root > old leaves. The relationship between GSLs accumulation and expression of GSLs biosynthesis MYB TFs genes in different organs may be helpful to understand the mechanism of MYB TFs regulating GSL biosynthesis in Chinese cabbage.

Induced Production of 1-Methoxy-indol-3-ylmethyl Glucosinolate by Jasmonic Acid and Methyl Jasmonate in Sprouts and Leaves of Pak Choi (Brassica rapa ssp. chinensis)

Pak choi plants (Brassica rapa ssp. chinensis) were treated with different signaling molecules methyl jasmonate, jasmonic acid, linolenic acid, and methyl salicylate and were analyzed for specific changes in their glucosinolate profile. Glucosinolate levels were quantified using HPLC-DAD-UV, with focus on induction of indole glucosinolates and special emphasis on 1-methoxy-indol-3-ylmethyl glucosinolate. Furthermore, the effects of the different signaling molecules on indole glucosinolate accumulation were analyzed on the level of gene expression using semi-quantitative realtime RT-PCR of selected genes. The treatments with signaling molecules were performed on sprouts and mature leaves to determine ontogenetic differences in glucosinolate accumulation and related gene expression. The highest increase of indole glucosinolate levels, with considerable enhancement of the 1-methoxy-indol-3-ylmethyl glucosinolate content, was achieved with treatments of sprouts and mature leaves with methyl jasmonate and jasmonic acid. This increase was accompanied by increased expression of genes putatively involved in the indole glucosinolate biosynthetic pathway. The high levels of indole glucosinolates enabled the plant to preferentially produce the respective breakdown products after tissue damage. Thus, pak choi plants treated with methyl jasmonate or jasmonic acid, are a valuable tool to analyze the specific protection functions of 1-methoxy-indole-3-carbinole in the plants defense strategy in the future.

Assessment of the Anticancer Compounds Se-Methylselenocysteine and Glucosinolates in Se-Biofortified Broccoli (Brassica oleracea L. var. italica) Sprouts and Florets

Broccoli (Brassica oleracea L. var. italica) is a rich source of chemopreventive compounds. Here, we evaluated and compared the effect of selenium (Se) treatment on the accumulation of anticancer compounds Se-methylselenocysteine (SeMSCys) and glucosinolates in broccoli sprouts and florets. Total Se and SeMSCys content in sprouts increased concomitantly with increasing Se doses. Selenate was superior to selenite in inducing total Se accumulation, but selenite is equally effective as selenate in promoting SeMSCys synthesis in sprouts. Increasing sulfur doses reduced total Se and SeMSCys content in sprouts treated with selenate, but not in those with selenite. Examination of five broccoli cultivars reveals that sprouts generally have better fractional ability than florets to convert inorganic Se into SeMSCys. Distinctive glucosinolate profiles between sprouts and florets were observed, and sprouts contained approximately 6-fold more glucoraphanin than florets. In contrast to florets, glucosinolate content was not affected by Se treatment in sprouts. Thus, Se-enriched broccoli sprouts are excellent for simultaneous accumulation of chemopreventive compounds SeMSCys and glucoraphanin.

Hairy roots, callus, and mature plants of Arabidopsis thaliana exhibit distinct glucosinolate and gene expression profiles

Hairy root cultures transformed with Agrobacterium rhizogenes or undifferentiated callus cultures are used for production of plant secondary metabolites. Glucosinolates (GS) are a group of secondary metabolites that produce a variety of bioactive compounds upon hydrolysis. Several studies report the successful production of high concentrations of secondary metabolites in vitro. However, such cultivation methods can significantly change metabolic profiles, and the mechanism behind this to be rarely understood. Therefore, we compared the GS and transcript profiles of Arabidopsis thaliana leaves and roots with hairy root and callus in vitro cultures. Compared to the roots of intact A. thaliana plants, overall, hairy roots contained lower GS levels. In particular, lower quantities of short-chain aliphatic GS were observed and a larger proportion of long-chain aliphatic GS on total content. Corresponding, the transcript levels of most aliphatic biosynthetic genes (MAM1, CYP79F1, CYP83A1, UGT74C1, and SUR1) were significantly lower in hairy root cultures compared to roots of intact plants. In callus culture, the lowest transcripts levels were detected for overall GS biosynthetic genes with an absence of aliphatic GS. From the indole group, 1-methoxy-indol-3-ylmethyl GS was found to be a major component in hairy root cultures and roots whereas indol-3-ylmethyl GS dominated in leaves and 4-hydroxy-indol-3-ylmethyl GS in callus cultures. Leaves of intact plants contained the highest amounts of GS. Here, aliphatic short-chain GS dominated which was in accordance with transcript levels of aliphatic biosynthetic genes. The study reveals tissue-specific accumulation of GS and transcript pattern in plants distinct from in vitro culture systems.

Variation of major glucosinolates in different varieties and lines of rocket salad

Glucosinolate (GSL) contents in five varieties and eleven lines of rocket salad (Eruca sativa L.) were quantified using HPLC-UV at 227 nm. Eleven GSLs including five aliphatic (glucoraphanin, glucothiobeinin, glucobrassicanapin, glucoerucin, and dimeric 4-mercaptobutyl GSL), two indolyl (glucobrassicin and 4-methoxyglucobrassicin), one aromatic (gluconasturtiin) and three unknown GSLs were identified based on our data base. Aliphatic GSLs were noted as the predominant group with an average 89% of the total content. The highest total GSL amounts were documented in ‘Herb-Fragrant Vegetable’ (31.12 μol·g−1 dry weight (DW)), whereas the lowest was in line 28612 (9.91). Relatively 73% of lines among the lines documented the content more than 8 μmol·g−1 DW of dimeric 4-mercaptobutyl GSL, particularly lines 28615 and 28619 noted more than > 17 μmol·g−1 DW. The sum of three major GSLs (glucoraphanin, glucoerucin, and dimeric 4-mercaptobutyl GSL) attributed > 8 μmol·g−1 DW in all rocket salads, especially ‘Herb-Fragrant Vegetable’ and line 28613 (87 and 93% respectively) in the total GSL accumulation, likewise line 28612 and 28620 attributed > 90%. Indolyl GSLs were ranged 0.27–1.09 μmol·g−1 DW, accounted less than 6% of the total GSLs in varieties and lines. These results provide valuable information regarding the potential beneficial GSL contents individually in different varieties and lines of rocket salads.

Glucosinolate Biosynthesis in Hairy Root Cultures of Broccoli (Brassica oleracea var. italica)

Here we present previously unreported glucosinolate production by hairy root cultures of broccoli (B. oleracea var. italica). Growth media greatly influenced the growth and glucosinolate content of hairy root cultures of broccoli. Seven glucosinolates, glucoraphanin, gluconapin, glucoerucin, glucobrassicin, 4-methoxyglucobrassicin, gluconasturtiin, and neoglucobrassicin, were identified by analysis of the broccoli hairy root cultures. Both half and full strength B5 and SH media enabled the highest accumulation of glucosinolates. In most cases, the levels of glucosinolates were higher in SH and BS media. Among the 7 glucosinolates, the accumulation of neoglucobrassicin was very high, irrespective of growth medium. The neoglucobrassicin content was 7.4-fold higher in SH medium than 1/2 MS, in which its level was the lowest. The 1/2 B5 medium supported the production of the highest amounts of glucobrassicin and 4-methoxyglucobrassicin, the levels for which were 36.2- and 7.9- fold higher, respectively, than their lowest content in 1/2 MS medium. The 1/2 SH medium enabled the highest accumulation of glucoraphanin and gluconapin in the broccoli hairy root cultures, whose levels were 1.8- and 4.6-fold higher, respectively, than their lowest content in 1/2 MS medium. Our results suggest that hairy root cultures of broccoli could be a valuable alternative approach for the production of glucosinolate compounds.

Glucose signalling positively regulates aliphatic glucosinolate biosynthesis

The effects of glucose on aliphatic glucosinolate biosynthesis in Arabidopsis thaliana were investigated in this study by using mutants related to aliphatic glucosinolate biosynthesis and regulation, as well as glucose signalling. The results showed that glucose significantly increased the contents of individual and total aliphatic glucosinolates. Expression of MYB28 and MYB29, two key transcription factors in aliphatic glucosinolate biosynthesis, was also induced by glucose. Consistently, the increased accumulation of aliphatic glucosinolates and the up-regulated expression of CYP79F1 and CYP79F2 induced by glucose disappeared in the double mutant myb28myb29. MYB28 and MYB29 synergistically functioned in the glucose-induced biosynthesis of aliphatic glucosinolates, but MYB28 was predominant over MYB29. Interestingly, the content of total aliphatic glucosinolates and the expression level of MYB28 and MYB29 were substantially reduced in the glucose insensitive mutant gin2-1 and the ABA insensitive 5 (abi5-7) mutant compared with the wild type. In addition, total aliphatic glucosinolates accumulated much less in another sugar-insensitive RGS1 (regulator of G-protein signaling 1) mutant (rgs1-2) than in the wild type. These results suggest that glucose-promoted aliphatic glucosinolate biosynthesis is regulated by HXK1- and/or RGS1-mediated signalling via transcription factors, MYB28, MYB29, and ABI5.

Temperature-induced Glucosinolate Accumulation Is Associated with Expression of BrMYB Transcription Factors

Turnips (Brassica rapa. subsp. rapa L.) produce glucosinolates (GSLs), thioglucosides whose hydrolyzed derivatives have been shown to provide chemopreventive benefits. Two cultivars of turnips [‘Just Right’ (JR) and ‘Scarlet Queen’ (SQ)] were grown under three different temperature regimes to assess the role of temperature on GSL production in roots and shoots. When compared with low-temperature treatments, high-temperature treatments increased total and individual GSLs in a tissue- and genotype-specific manner. When compared with low-temperature treatments, total GSLs were ≈70% and 130% higher in JR shoots and roots, respectively, grown at high-temperature treatments. High temperatures also increased total GSLs in SQ shoots and roots by ≈80% and 85%, respectively, when compared with low temperatures. Gluconasturtiin (GNS, 2-phenylethyl GSL) concentration was inversely correlated with temperature with high-temperature treatments resulting in 20% and 48% less GNS than low-temperature treatments in JR and SQ roots, respectively. The indolic GSL, 1-methoxyglucobrassicin (1MGB; 1-methoxy-3-ylmethyl GSL), was the root GSL most elevated by increased temperature resulting in a 1000% increase on average in both cultivars between the low- and high-temperature treatments. These results show promise for the use of temperature to enhance the health-promoting properties of turnip because 1MGB has potent chemopreventive effects. Gene expression analysis suggests that some BrMYB transcription factor expression levels are associated with temperature-dependent changes in GSL accumulation; however, this association varies between cultivar and tissue type.