Submitted to: American Society for Horticultural Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/16/2000
Publication Date: N/A
Citation: Interpretive Summary: Broccoli is well known as a source of plant compounds known as glusinolates. One of these, glucoraphanin, is known to form a compound called sulforaphane. In research trials, it has been shown that rats fed sulforaphane or broccoli extracts have a lower risk of cancer than rats not fed these materials. Evidence indicates that sulforaphane protects cells against cancer-causing agents by inducing the detoxification of those agents. Thus, a diet rich in broccoli may protect humans against certain cancers. We are interested in knowing if glucoraphanin levels and the detoxifying activity of broccoli can be altered. If we can increase these factors, this might enhance the capacity of broccoli to protect people against cancer. Specific goals of this research were to determine how variable glucoraphanin content and detoxifying activity are among USDA broccoli varieties and if we can identify individuals that have consistently high or low levels of these factors. Results show that detoxifying activity and glucoraphanin content vary widely among USDA varieties and that individuals with high or low levels can be selected. In this study, varieties with high glucoraphanin also had high detoxifying activity while varieties with low glucorpahanin had little activity. These results support the idea that glucoraphanin is the primary agent in broccoli that induces detoxifying activity. Commercial and public broccoli breeders will use this information in their efforts to genetically enhance healthful attributes of broccoli. Identified varieties with high and low levels of glucoraphanin will be useful to medical researchers interested in fully testing the capacity of broccoli to protect cells against cancer.
Technical Abstract: The glucosinolate, Glucoraphanin (GR), is abundant in broccoli. The isothiocyanate congener of GR is sulforaphane, which has been shown to be a potent inducer of mammalian detoxication (Phase 2) enzyme activity and protector against tumorigenesis in animal models. Phenotypic variation in broccoli for Phase 2 enzyme (e.g., quinone reductase) activity has not been examined. Thus, this study was undertaken to evaluate: 1) quinone reductase induction potential (QRIP) variation among broccoli inbreds; 2) QRIP levels in selected lines; 3)correlation of QRIP with other traits; 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 fr. wt. These values were highly correlated with GR concentrations ranging from 0.04 to 2.94 umol/g fr. wt. A select subset of lines evaluated in 1996, were reevaluated in 1997, and the QRIP and GR 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). Also, both QRIP and GR concentration were highly correlated with days from transplant to harvest. Average F1 hybrid values for QRIP and GR in 1997 typically fell between their parental means, but were often below the midparent, resulting in negative heterosis. Results indicate selection for QRIP expression can effectively identify enhanced inbred lines. Evidence is also provided that there is a significant genetic component to both QRIP and GR levels, and that selection for either may provide an effective means to develop hybrids with enhanced chemoprotective attributes.