Broccoli is receiving increased attention because its florets are rich in many chemoprotective phytochemicals such as glucosinolates (GSs). Epidemiological studies have shown that diets rich in cruciferous (Brassicaceae) vegetables, especially broccoli, may provide protection against various forms of cancer, including colon and prostate cancer, particularly in the early initiation stages (Higdon et al., 2007). In addition, protective effects of broccoli against cardiovascular diseases have also been noted (Zhang et al., 2011).
Current research has demonstrated that the chemoprotective properties of cruciferous vegetables are attributed to GS hydrolysis products, primarily, isothiocyanates [ITCs (Traka and Mithen, 2009; Verkerk et al., 2009)]. Glucosinolates, consisting of β-thioglucoside N-hydroxysulfate, a side chain, and a β-d-glucopyranose moiety, are divided into three groups based on their amino acid precursors: aliphatic GSs (methionine, leucine, iso-leucine), indole GSs (tryptophan), and aromatic GSs (phenylalanine) (Table 1) (Sønderby et al., 2010b). On tissue damage, GSs can be hydrolyzed to several classes of bioactive breakdown products, including ITCs, thiocyanates, and nitriles, by typical plant myrosinases [β-thioglucoside glucohydrolase (EC 184.108.40.206)], which are compartmentalized either in specialized myrosin cells in the phloem parenchyma or in stomata cells (Burow and Wittstock, 2010). In addition, some bacteria in the gastrointestinal tract show myrosinase activity (Traka and Mithen, 2009). Among the hydrolysis products, many ITCs, particularly sulforaphane (SF), derived from the hydrolysis of aliphatic GSs, have shown high anticarcinogenic activity in mammalian cells (Traka and Mithen, 2009). SF has been studied extensively; this ITC is hydrolyzed from glucoraphanin, which is abundant in broccoli florets, seeds, and sprouts. The anticarcinogenic mechanism of ITCs, and particularly of SF, have been reviewed in previous studies (Traka and Mithen, 2009; Verkerk et al., 2009). Recent studies have suggested that SF prevents vascular diseases by acting as an indirect antioxidant through the activation of Nrf-2 (Xue et al., 2008) and protects against ischemic–reperfusion injury of the heart through the antioxidant pathway and mitochondrial KATP channels (Piao et al., 2010). It is notable that hepatic, colonic mucosal, and pancreatic quinone reductase and glutathione S-transferase activities were induced by high doses of SF but not by SF nitrile (Matusheski and Jeffery, 2001). Moreover, the activity of specifier proteins such as epithiospecifier protein in broccoli could inhibit the formation of SF (Matusheski et al., 2004). However, proper cooking (e.g., blanching for 2 min, short-term boiling, or microwave treatment) without macerating broccoli florets can efficiently inactivate endogenous S-glycosyl hydrolases and specifier proteins; intact GSs can then be degraded by colonic microflora to promote the formation of health-benefitting ITCs (Matusheski et al., 2004; Sarikamis et al., 2006).
Trivial and chemical names of main glucosinolates identified in broccoli.
Some hydrolysis products derived from alkenyl GSs, including 2-(R)-hydroxy-3-butenyl GS, 2-propenyl GS (sinigrin), and 3-butenyl GS (gluconapin), also possess a degree of anticarcinogenic activity (Fahey et al., 1997), but these compounds may have adverse health effects (Verkerk et al., 2009). For example, oxazolidine-2-thiones formed from progoitrin and found in rapeseed have been associated with goiter and other negative effects in animals, including depressed growth, poor egg production, and liver damage (Tripathi and Mishra, 2007). To date, despite a lack of evidence for a goitrogenic effect of progoitrin and its breakdown products in humans (Traka and Mithen, 2009), the potential health risks may discourage people from consuming foods containing relatively high concentrations of this chemical. The alkenyl GSs and neoglucobrassicin also contribute to the pungent, bitter taste of some Brassica vegetables (Drewnowski and Gomez-Carneros, 2000; Schonhof et al., 2004). Some broccoli lines (e.g., ‘Shogun’, Eu8-1, and ‘Lvxiong90’) with relatively higher concentrations of alkenyl GSs (particularly progoitrin) were identified in previous studies (Brown et al., 2002; Kushad et al., 1999; Rosa and Rodrigues, 2001; Schonhof et al., 2004; Wang et al., 2012).
Indole-3-carbinol and diindolylmethane, two major hydrolysis products of glucobrassicin that are abundant in cruciferous plants, exhibit protective activities against many types of cancer, particularly hormone-responsive conditions, including breast, prostate, and ovarian cancers (Higdon et al., 2007). However, these compounds might also promote carcinogenesis by inducing phase-I enzymes, which can oxidize inert polyaromatic hydrocarbons to DNA-binding products (Baird et al., 2005). A recent study further demonstrated that the neoglucobrassicin/myrosinase complex showed strongly mutagenic properties in bacterial and mammalian cells (Glatt et al., 2011). Considering these findings, consumption of large amounts of indole glucosinolates should be approached with caution.
The composition and concentration of aliphatic GSs are mainly determined by the genotype of B. oleracea vegetables, although they can also be affected by many exogenous factors (Brown et al., 2002; Farnham et al., 2004; Ku et al., 2013; Schonhof et al., 2004). Compared with other Brassica vegetables, broccoli florets contain higher concentrations of glucoraphanin and comparatively low concentrations of other methionine-derived GSs (Verkerk et al., 2009). Some pure lines high in glucoraphanin were found in previous investigations of GSs in broccoli germplasm (Farnham et al., 2000; Kushad et al., 1999; Wang et al., 2012). Attempts have been made to breed broccoli with enhanced concentrations of 3-methylsulfinylpropyl GS (glucoiberin) and glucoraphanin to enhance health benefits (Faulkner et al., 1998; Mithen et al., 2003; Sarikamis et al., 2006). Sarikamis et al. (2006) bred a hybrid (48-13-4 × Br9) that shows an ≈2-fold increase in glucoraphanin concentration compared with commercial cultivars.
Various strategies for enhancing concentrations of chemoprotective GSs and decreasing concentrations of antinutritional GSs in Brassica vegetables were proposed by Verkerk et al. (2009). Previously, 14 pure broccoli lines with glucoraphanin concentrations more than 2-fold higher than those of commercial hybrids were obtained as candidates for breeding high-GS cultivars (Wang et al., 2012). In the present study, 10 parental lines—eight high-glucoraphanin lines screened previously and two lines with good agronomic characteristics—were used to breed high-glucoraphanin F1 hybrids (Table 2). We first evaluated two major commercial cultivars, Youxiu and Lvxiong90, which exhibited the highest concentrations of glucoraphanin and progoitrin, respectively, among commercial cultivars in our previous investigation (Wang et al., 2012), and six trial cultivars (Table 2). The reference cultivar with the highest concentration of glucoraphanin was determined as the final control, and the high-glucoraphanin hybrids were evaluated in comparison with this control. We also identified and analyzed 16 F1 hybrids with more than 3-fold higher glucoraphanin content than the controls for individual GSs and groups and two parental lines were validated as high-glucoraphanin types.
Code, name, source, planting location, and type of commercial cultivars, trial cultivars, and parental lines used in this study of high-glucoraphanin broccoli.
AbercrombieJ.M.FarnhamM.W.RushingJ.W.2005Genetic combining ability of glucoraphanin level and other horticultural traits of broccoliEuphytica143145151
BairdW.M.HoovenL.A.MahadevanB.2005Carcinogenic polycyclic aromatic hydrocarbon-DNA adducts and mechanism of actionEnviron. Mol. Mutagen.45106114
BrownA.F.YousefG.G.JefferyE.H.KleinB.P.WalligM.A.KushadM.M.JuvikJ.A.2002Glucosinolate profiles in broccoli: Variation in levels and implications in breeding for cancer chemoprotectionJ. Amer. Soc. Hort. Sci.127807813
BurowM.WittstockU.2010Glucosinolate breakdown in Arabidopsis: Mechanism regulation and biological significance. The arabidopsis book. 8:e0134. 16 May 2014. <http://www.bioone.org/doi/abs/10.1199/tab.0134>
CarlsonD.G.DaxenbichlerM.E.Van EtternC.H.KwolekW.F.WilliamsP.H.1987Glucosinolates in crucifer vegetables: Broccoli, brussels sprouts, cauliflower, collards, kale, mustard greens, and kohlrabiJ. Amer. Soc. Hort. Sci.112173178
FaheyJ.W.ZhangY.S.TalalayP.1997Broccoli sprouts: An exceptionally rich source of inducers of enzymes that protect against chemical carcinogensProc. Natl. Acad. Sci. USA941036710372
FarnhamM.W.StephensonK.K.FaheyJ.W.2000Capacity of broccoli to induce a mammalian chemoprotective enzyme varies among pure linesJ. Amer. Soc. Hort. Sci.125482488
FarnhamM.W.WilsonP.E.StephensonK.K.FaheyJ.W.2004Genetic and environmental effects on glucosinolate content and chemoprotective potency of broccoliPlant Breed.1236065
FaulknerK.MithenR.WilliamsonG.1998Selective increase of the potential anticarcinogen 4-methylsulphinylbutyl glucosinolate in broccoliCarcinogenesis19605609
GigolashviliT.BergeB.FlüggeU.2009Specific and coordinated control of indolic and aliphatic glucosinolate biosynthesis by R2R3-MYB transcription factors in Arabidopsis thalianaPhytochem. Rev.8313
GlattH.Baasanjav-GerberC.SchumacherF.MonienB.H.SchreinerM.FrankH.SeidelA.EngstW.20111-Methoxy-3-indolylmethyl glucosinolate: A potent genotoxicant in bacterial and mammalian cells: Mechanisms of bioactivationChemico-Biol. Interaction1928186
GuH.ZhaoZ.ShengX.YuH.WangJ.2014Efficient doubled haploid production in microspore culture of loose-curd cauliflower (Brassica oleracea var. botrytis)Euphytica195467475
HigdonJ.V.DelageB.WilliamsD.E.DashwoodR.H.2007Cruciferous vegetables and human cancer risk: Epidemiologic evidence and mechanistic basisPharmacol. Res.55224236
KuK.M.JefferyE.H.JuvikJ.A.2013Influence of seasonal variation and methyl jasmonate mediated induction of glucosinolate biosynthesis on quinone reductase activity in broccoli floretsJ. Agr. Food Chem.6196239631
KushadM.M.BrownA.F.KurilichA.C.JuvikJ.A.KleinB.P.WalligM.A.JefferyE.H.1999Variation of glucosinolates in vegetable crops of Brassica oleraceaJ. Agr. Food Chem.4715411548
LiG.QuirosC.F.2003In planta side-chain glucosinolate modification in Arabidopsis by introduction of dioxygenase Brassica homolog BoGSL-ALKTheor. Appl. Genet.10611161121
MatusheskiN.V.JefferyE.H.2001Comparison of the bioactivity of two glucoraphanin hydrolysis products found in broccoli, sulforaphane and sulforaphane nitrileJ. Agr. Food Chem.4957435749
MatusheskiN.V.JuvikJ.A.JefferyE.H.2004Heating decreases epithiospecifier protein activity and increases sulforaphane formation in broccoliPhytochemistry6512731281
MatusheskiN.V.SwarupR.JuvikJ.A.MithenR.BennettM.JefferyE.H.2006Epithiospecifier protein from broccoli (Brassica oleracea L. ssp. italica) inhibits formation of the anticancer agent sulforaphaneJ. Agr. Food Chem.5420692076
MithenR.FaulknerK.MagrathR.RoseR.WilliamsonG.MarquezJ.2003Development of isothiocyanate-enriched broccoli and its enhanced ability to induce phase 2 detoxification enzymes in mammalian cellsTheor. Appl. Genet.106727734
Nour-EldinH.H.AndersenT.G.BurowM.MadsenS.R.JøgensenM.E.OlsenC.E.DreyerI.HedrichR.GeigerD.HalkierB.A.2012NRT/PTR transporters are essential for translocation of glucosinolate defence compounds to seedsNature488531534
PiaoC.S.GaoS.LeeG.H.KimD.S.ParkB.H.ChaeS.W.KimS.H.2010Sulforaphane protects ischemic injury of hearts through antioxidant pathway and mitochondrial KATP channelsPharmacol. Res.61342348
RosaE.A.S.RodriguesA.S.2001Total and individual glucosinolate content in 11 broccoli cultivars grown in early and late seasonsHortScience365659
SchonhofI.KrumbeinA.BrücknerB.2004Genotypic effects on glucosinolates and sensory properties of broccoli and cauliflowerFood/Nahrung12533
SønderbyI.E.BurowM.RoweH.C.KliebensteinD.J.HalkierB.A.2010aA complex interplay of three R2R3 MYB transcription factors determines the profile of aliphatic glucosinolates in ArabidopsisPlant Physiol.153348363
VallejoF.Tomás-RarberánF.A.Bennavente-GaracíaA.G.García-VgueraC.2003Total and individual glucosinolate contents in inflorescences of eight broccoli cultivars grown under various climatic and fertilization conditionsJ. Sci. Food Agr.83307313
VerkerkR.SchreinerM.KrumbeinA.CiskaE.HolstB.RowlandI.SchrijverR.D.HansenM.GerhäuserC.MithenR.DekkerM.2009Glucosiolates in Brassica vegetables: The influence of the food supply chain on intake, bioavailability and human healthMol. Nutr. Food Res.53S219S265
WangJ.GuH.YuH.ZhaoZ.ShengX.ZhangX.2012Genotypic variation of glucosinolates in broccoli (Brassica oleracea var. italica) florets from ChinaFood Chem.133735741
WilliamsD.J.CritchleyC.PunS.NottinghamS.O'HareT.J.2008Epithiospecifier protein activity in broccoli: The link between terminal alkenyl glucosinolates and sulphoraphane nitrilePhytochemistry6927652773
XueM.QianQ.AdaikalakoteswariA.RabbaniN.Babaei-JadidiR.ThornalleyP.J.2008Activation of NF-E2-related factor-2 reverses biochemical dysfunction of endothelial cells induced by hyperglycemia linked to vascular diseaseDiabetes5728092817
ZhangX.ShuX.O.XiangY.B.YangG.LiH.GaoJ.CaiH.GaoY.T.ZhengW.2011Cruciferous vegetable consumption is associated with a reduced risk of total and cardiovascular disease mortalityAmer. J. Clin. Nutr.94240246
Comparison of individual glucosinolates and each group of glucosinolates among high-glucoraphanin broccoli hybrids.z
The head diameter and head weight of broccoli lines planted in the field.z