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
Honghui Gu, Jiansheng Wang, Huifang Yu, Zhenqing Zhao, Xiaoguang Sheng, Jisuan Chen and Yingjun Xu
Mark W. Farnham, Jed W. Fahey and Katherine K. Stephenson
Broccoli (Brassica oleracea L. Italica Group) is a rich source of the aliphatic glucosinolate glucoraphanin. The glucoraphanin breakdown product, sulforaphane, has been shown to induce Phase II detoxication enzymes (e.g., Quinone Reductase) and has attracted attention as a potential chemoprotector against cancer. The objectives of this research were to evaluate the concentration of glucoraphanin in an array of diverse broccoli inbreds (doubled-haploids) largely derived from commercial germplasm and to determine if expression of glucoraphanin level in this initial evaluation is correlated with expression in a subsequent environment. In 1996, individual florets from single broccoli heads were sampled from 75 inbred lines grown in the field at Charleston, S.C., and glucoraphanin concentration was assayed. In this test, concentrations ranged from 0.04 to 2.94 μmol glucoraphanin per g fresh weight of florets and the mean concentration was 0.86. In 1997, a subset of 22 inbreds analyzed the first year were grown again in a replicated field trial. This inbred subset was made up of lines with diverse pedigrees and with high, low, or intermediate glucoraphanin concentrations. In this second year, glucoraphanin concentration had a range from 0.24 to 2.99 μmol per g fresh weight of florets and a mean of 1.37. Correlation of entry mean glucoraphanin concentration in 1997 with that in 1996 was positive (r = 0.79) and highly significant (P < 0.001) indicating that floret glucoraphanin concentration was relatively consistent between years. These observations provide evidence that floret glucoraphanin concentration has a significant genetic component.
Mark W. Farnham, Katherine K. Stephenson and Jed W. Fahey
Broccoli (Brassica oleracea L., Italica Group) seed and resulting sprouts can contain high levels of glucoraphanin, a glucosinolate, which can be converted to sulforaphane, a compound with cancer protective and antioxidant properties. This observation has stimulated interest in broccoli seed production. In this study, inbred lines, which produce relatively high yields of homogeneous, selfed-seed across different environments in the absence of insect pollinators, were used to evaluate the relative importance of genotype versus environment as a determinant of glucoraphanin concentration in broccoli seed. Glucoraphanin and glucoiberin were measured in broccoli seed lots generated from ten broccoli inbred lines grown in two greenhouse and two screen cage environments. Typically, seed glucoraphanin level ranged from 5 to 100 μmol·g-1 seed and glucoiberin ranged from 0 to about 40 μmol·g-1 seed, regardless of the environment in which seed was produced. Analysis of variance indicated that genotype was the most significant factor influencing levels of the two glucosinolates. Although significant environmental and genotype × environment effects were observed for glucoraphanin and a significant genotype × environment effect was observed for glucoiberin, these effects were small compared to the genotype effects. Results indicate that it is possible to identify broccoli inbreds that consistently produce relatively high yields of seed with a high glucoraphanin content across different environments.
Dean A. Kopsell and Carl E. Sams
vegetables are relatively abundant sources of antioxidants with potential anticarcinogenic activity ( Kurilich et al., 1999 ). The bioactive compounds in Brassicas include lutein and β-carotene carotenoids, glucoraphanin and glucobrassicin glucosinolates
Allan F. Brown, Gad G. Yousef, Elizabeth H. Jeffery, Barbara P. Klein, Mathew A. Wallig, Mosbah M. Kushad and John A. Juvik
Ten broccoli [Brassica oleracea L. (Botrytis Group)] accessions were grown in several environments to estimate glucosinolate (GS) variability associated with genotype, environment, and genotype × environment interaction and to identify differences in the stability of GSs in broccoli florets. Significant differences in genetic variability were identified for aliphatic GSs but not for indolyl GSs. The percentage of GS variability attributable to genotype for individual aliphatic compounds ranged from 54.2% for glucoraphanin to 71.0% for progoitrin. For total indolyl GSs, the percentage of variability attributable to genotype was only 12%. Both qualitative and quantitative differences in GSs were detected among the genotypes. Ten-fold differences in progoitrin, glucoraphanin, and total aliphatic GS levels were observed between the highest and lowest genotypes. Only two lines, Eu8-1 and VI-158, produced aliphatic GSs other than glucoraphanin in appreciable amounts. Differences in stability of these compounds among the cultivars were also observed between fall and spring plantings. Results suggest that genetic factors necessary for altering the qualitative and quantitative aliphatic GS profiles are present within existing broccoli germplasm, which makes breeding for enhanced cancer chemoprotectant activity feasible.
G. Li, A. Riaz, S. Goyal, S. Abel and C.F. Quiros
Inheritance of three major genes involved in synthesis of aliphatic glucosinolates (GSL) was followed in segregating populations of Brassica oleracea L. generated from three crosses: broccoli × cauliflower, collard × broccoli, and collard × cauliflower. Two of these genes, GSL-PRO and GSL-ELONG, regulate sidechain length. The action of the former results in three-carbon GSL, whereas action of the latter produces four-carbon GSL. We determined that these two genes act and segregate independently from each other in B. oleracea. The double recessive genotype produces only trace amounts of aliphatic GSL. The third gene, GSL-ALK controls sidechain desaturation and, as it has been observed in Arabidopsis thaliana (L.) Heynh., we found that this gene cosegregates with a fourth gene, GSL-OH, that is responsible for sidechain hydroxylation. Elucidation of the inheritance of major genes controlling biosynthesis of GSL will allow for manipulation of these genes and facilitate development of lines with specific GSL profiles. This capability will be important for improvement of Brassica breeding lines with high content of desirable GSL, like glucoraphanin, a demonstrated precursor of anticarcinogenic compounds. Additionally, this work is the first step towards cloning the major genes of the aliphatic GSL pathway, and to use these clones in transformation strategies for further crop enhancement.
Mark W. Farnham
it. ‘Hi-Test’ is a self-compatible, inbred cultivar that yields high-quality, uniform seed, containing high levels of the glucosinolate glucoraphanin (GR). This variety has very uniform growth characteristics, plant size, seed yield, and chemical
Craig S. Charron and Carl E. Sams
Crops of the Brassicaceae contain glucosinolates(GSs), which when hydrolyzed by the enzyme myrosinase, generate products involved in cancer chemoprotection, plant defense, and plant-insect interactions. A rapid-cycling base population of B. oleracea L. was grown in a hydroponic system in a controlled environment to determine the roles of temperature, photosynthetic photon flux (PPF), and photoperiod in GS concentration and myrosinase activity. The concentration of total GSs in leaves was 44% and 114% higher at 12 and 32 °C respectively than at 22 °C under constant light of 300 μmol·m-2·s-1. The concentration of glucoraphanin, the precursor to sulforaphane, a compound with chemoprotective properties, was 5-fold higher at 32 than at 22 °C. Total GSs were ≈50% lower in roots at 12 °C and 32 than at 22 °C. Total GSs in leaves decreased 20% when PPF was increased from 200 to 400 μmol·m-2·s-1. Myrosinase activity on a fresh weight basis (activity-FW) was ≈30% higher in leaves and stems at 12 and 32 °C than at 22 °C, and ≈30% higher in leaves grown at 200 and 400 μmol·m-2·s-1 than at 300 μmol·m-2·s-1. Consideration of climatic factors that influence the glucosinolate-myrosinase system may be necessary to optimize the planting and cultivation of Brassica crops for maximum health benefits.
Mark W. Farnham, Katherine K. Stephenson and Jed W. Fahey
Broccoli (Brassica oleracea L., Italica Group) has been recognized as a source of glucosinolates and their isothiocyanate metabolites that may be chemoprotective against human cancer. A predominant glucosinolate of broccoli is glucoraphanin and its cognate isothiocyanate is sulforaphane. Sulforaphane has been shown to be a potent inducer of mammalian detoxication (Phase 2) enzyme activity and to inhibit chemical-induced tumorigenesis in animal models. Little is known about phenotypic variation in broccoli germplasm for Phase 2 enzyme (e.g., quinone reductase) induction potential. Thus, this study was undertaken to evaluate: 1) quinone reductase induction potential (QRIP) diversity among a population of broccoli inbreds; 2) QRIP levels in selected lines; 3) correlation of QRIP with other horticultural characteristics; and 4) QRIP expression in a sample of synthesized hybrids. In 1996, 71 inbreds and five hybrid checks (all field-grown), ranged from a QRIP of nearly zero to 150,000 units/g fresh weight (FW) (mean of 34,020 units/g FW). These values were highly correlated with methylsulphinylalkyl glucosinolate (MSAG; primarily glucoraphanin) concentrations that ranged from 0.04 to 2.94 μmol.g-1 FW. A select subset of lines evaluated in 1996 were reevaluated in 1997. QRIP and MSAG values in this second year were similar to and correlated with those observed in 1996 (r = 0.73, P < 0.0001 and r = 0.79, P < 0.0001, respectively). In addition, both QRIP and MSAG concentration were highly correlated with days from transplant to harvest. Average F1 hybrid values for QRIP and MSAG in 1997 fell typically between their parental means, but were often closer to the mean of the low parent. Results of this study indicate that divergent QRIP expression can effectively be used to select enhanced inbred lines to use in development of value-added hybrids. Evidence is also provided that there is a significant genetic component to both QRIP and MSAG concentration, and that selection for either one may provide an effective means for developing broccoli hybrids with enhanced chemoprotective attributes. Chemical names used: 4-methylsulphinylbutyl glucosinolate (glucoraphanin) and 4-methylsulphinylbutyl isothiocyanate (sulforaphane).
Timothy W. Coolong, William M. Randle, Heather D. Toler and Carl E. Sams
Rapid cycling Brassica rapa L. were grown for 7 days in the presence of 11 levels of zinc (Zn) in hydroponic solution culture and evaluated for changes in Zn and glucosinolate (GS) content. Zinc levels were 0.05, 1, 5, 10, 25, 50, 75, 100, 125, 150, and 200 mg·L-1 Zn. Plants grown in solutions with ≥50 mg·L-1 Zn displayed severe Zn toxicity symptoms, grew little, or died and were not subsequently evaluated for GS content. Shoot Zn concentrations increased linearly with increasing Zn treatment levels. Gluconapin, which accounted for nearly 90% of the aliphatic GSs present, was the only aliphatic GS influenced by Zn, and decreased linearly with increasing Zn levels. Accumulation of glucobrassicin and 4-methoxyglucosbrassicin, both indole GSs, responded with a linear increase and quadratically, respectively, to Zn fertility. An aromatic GS, gluconasturtiin, was also influenced by Zn levels in solution, and had a quadratic response to increasing Zn. This suggested that Zn fertility can influence changes in GS that may affect flavor (bitterness, etc.) or medicinal attributes associated with the GS and their breakdown products, as well as elevate the nutritional status of Zn in the leaves of Brassica.