Polyphenol oxidase (PPO) is a Type 3 copper protein, which catalyzes the oxidation of monophenols or o -diphenols to o -quinones ( Klabunde et al., 1998 ). PPO-generated quinones are highly reactive and will crosslink with proteins or polymerize
Matthew A. Escobar, Andrew Shilling, Pine Higgins, Sandra L. Uratsu and Abhaya M. Dandekar
María Daniela Mares-Quiñones and Juan Ignacio Valiente-Banuet
Piquin pepper [Capsicum annuum L. var. glabriusculum (Dunal) Heiser and Pickergill] is a semidomesticated pepper with high commercial value and wide applications as fresh or processed products. Piquin pepper plants have been difficult to domesticate and cultivate because of low seed germination, genetic and morphologic variability, insect and disease susceptibility, and limited environmental physiology information. Currently, seed sterility is no longer considered a limiting factor as hormonal, chemical, and thermal treatments have been developed to overcome seed dormancy. In vitro propagation (primarily by direct organogenesis) is still not reliable for seedling production. Cropping systems of piquin pepper plants include traditional methods such as agroforestry and full sunlight, and under protected horticulture conditions, mainly shade nets. Shade levels and water availability affect yield and vegetative growth. Piquin pepper plants can be grown under diverse geographic and edaphic conditions. Nutrition and fertilization studies are limited. Biotic stresses that can cause economic damage to piquin pepper plants include most that affect other pepper cultivars. Piquin pepper is also considered an important genetic resource as it reports resistance to some viral groups, which could be used for genetic improvement of other cultivated peppers. Current research needs involve the development of dependable plant materials (cultivated varieties) with reduced labor needs, particularly during the harvest period. In addition, research is needed to reduce the susceptibility of piquin pepper plants to other plant diseases. This review presents an analysis of the aspects related to the production of piquin peppers under cultivated conditions.
Suping Zhou, Roger Sauve, Tara Fish and Theodore W. Thannhauser
protein, ferredoxin-NADP (+) reductase and quinone oxidoreductase-like protein, and the reduction of rubisco activase ( Table 2 ). The expressed sequence tags (ESTs) for other proteins were not found on microarray chips; consequently, their transcriptional
Fan Zhang, Zi Wei, Peter Jeranyama, Carolyn DeMoranville and Harvey J.M. Hou
“area,” which is the quantity of fluorescence area above the transient curve, may represent the size of the PSII quinone pool ( Strasser et al., 2004 ). Figure 3 is a typical spider graph, which summarizes the six Chl fluorescence parameters of
Zi Wei, Peter Jeranyama, Fan Zhang, Carolyn DeMoranville and Harvey J.M. Hou
v /F m ) ( Strasser et al., 2004 ). The size of the PS II quinone pool may be expressed as “area,” which is the measurement of fluorescence area above the transient ( Strasser et al., 2004 ). The photosynthesis index is defined as a driving force of
G. Schnabel and C.H. Crisosto
Applications of the quinone outside inhibitor (QoI) fungicides azoxystrobin, kresoxim-methyl, trifloxystrobin, picoxystrobin, or pyraclostrobin can increase yield and quality of cereal crops, likely due to improved disease control ( Ammermann et al
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).
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.
Leslie A. Weston and Verónica M. Gonzalez
Sorgoleone, the oxidized quinone form of a hydrophobic p-benzoquinone was first isolated from Sorghum root exudates. Sorgoleone is a potent inhibitor of growth in several annual weed species and causes tissue bleaching at concentrations of <25 μ M. These investigations were designed to determine if soreoleone's allelopathic activity was related to an inhibition of photosynthetic electron transport. The effect of sorgoleone versus DCMU (diuron) on inhibition of O2 evolution by broken wheat thylakoids, and in oxygenevolving PSII membranes containing QA and QB primary and secondary electron acceptors in PSII was determined. Sorgoleone was a potent inhibitor of O2 evolution in this system with ∼ 0.04 and 0.78 μ M concentrations required for 50 and 100% inhibition as compared to -0.11 and 2.0 μ M DCMU, respectively. Sorgoleone caused no significant inhibition of PSI mediated photooxidation of ascorbate/dichlorophenolindophenol, establishing that the locus of inhibition by sorgoleone was within the PSII complex. The effect of trypsin treatment of chloroplasts and PSII membranes on sensitivity to inhibition by DCMU and sorgoleone was examined. The comparison of DCMU and sorgoleone upon the formation and decay of flash-induced chlorophyll a variable fluorescence indicates that sorgoleone specifically inhibited the oxidation of QA by QB.
Mitiku Girma and Alex I. Smirnov
Recent studies performed at the Univ. of Sheffield (Sheffield, England) have established a correlation between the onset of senescence and the loss of viability in plants with a development of stable free-radicals that can be observed by Electron Paramagnetic Resonance (EPR) spectroscopy. We explored the possibility of free-radical formation following root injury of corn seedlings (Zea mays L.). Free radical signals were detected by EPR spectroscopy at 9.5 GHz. In all cases, we observed a single-line free-radical signal (g value ≈2.004) superimposed with six-line EPR spectrum from Mn2 + ions naturally present in the plant tissues. We determined a consistent increase in the intensity of single-line EPR signal after inducing root injury. This signal presumably is attributed to a quinone-derived radical and, as speculated, is associated with stressed respiratory transport chains. Based on our results, we suggest that free-radical reactions can be induced by root injury. Furthermore, an appearance of free-radical signal in the root may serve as an indication of a stress, natural and induced. If the precursors of observed free-radical signal can be determined, this will provide better insight on free-radical processes in plants followed by an injury. This work used the resources of the Illinois EPR Research Center (NIH P4 1 -RR0 1811).