Rafael López-Valbuena

University of Cordoba (Spain), Cordoue, Andalusia, Spain

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Publications (8)11.94 Total impact

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    ABSTRACT: Induction of phytoalexin formation in roots of chickpea (Cicer arietinum L.) seedlings treated with the reduced form of glutathione (GSH) was investigated. Accumulation of phytoalexins and constitutive isoflavonoids upon GSH treatment was assessed by high performance liquid chromatography analysis of extracts from roots and liquid incubating media of seedlings, whereas the requirement for concurrent de novo synthesis of induced compounds was assessed in elicitation studies conducted in the presence of key enzyme inhibitors of the phenylpropanoid pathway and/or 〚U-14C〛-L-phenylalanine. The results indicate that: (a) GSH elicits the formation not only of the pterocarpan phytoalexins medicarpin and maackiain, but also that of the constitutive isoflavones biochanin A and formononetin and, in seedlings older than 4 d, that of the isoflavanones homoferreirin and cicerin. (b) GSH-induced secondary metabolites do not accumulate in plant root tissue; rather, they are released into the surrounding external medium. (c) Phytoalexins and isoflavonoids induced by GSH are de novo synthesized from early phenylpropanoid pathway precursors rather than derived from pre-existing conjugate forms or immediate precursors. (d) Because of metabolic competence and/or proximity, only a small proportion of root cells is responsive to GSH elicitation, hence the very small amounts or absence of induced compounds detected in root tissue samples.
    Plant Physiology and Biochemistry 09/2001; · 2.35 Impact Factor
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    ABSTRACT: Cited By (since 1996): 6, Export Date: 6 June 2011, Source: Scopus
    Minerva Biotecnologica. 01/2001; 13:93-95.
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    P J Palomo, Rafael López-Valbuena, Manuel Tena
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    ABSTRACT: In order to investigate the existence of genetic variability in antioxidant enzyme defenses in sunflower, twelve inbred lines, six cytoplasmic male-sterile and six restorer lines, commonly used in breeding programs have been compared with respect to (a) their levels of constitutive superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2) and guaiacol-dependent peroxidase (GPX, EC 1.11.1.7), and (b) their isoenzyme polymorphism in SOD, CAT, and GPX activities. Constitutive levels of antioxidant enzymes in the 2nd leaf pair of 15-20-day-old sunflower plants showed significant differences between lines. The ranges of variation in enzyme activities of the different lines were equivalent to 34.3% (CAT), 38.2% (SOD), 59.5% (APX), 60.0% (GR), and 62.9% (GPX) of the respective maximal values. Isoenzyme profiles of CAT, GPX and SOD revealed the existence in sunflower of at least three, six and four isoforms of these enzymes, respectively. Further characterization of SOD isoenzymes revealed that no isoenzyme corresponded to a Mn-SOD, the faster moving isoform being a Cu/Zn-SOD and the remainder three Fe-SODs. Among the twelve inbred sunflower lines studied there were ample qualitative, and sometimes quantitative too, differences in isoenzyme dotation of CAT, GPX and Fe-SOD.
    Free Radical Research 01/2000; 31 Suppl:S227-33. · 2.99 Impact Factor
  • J Jorrín, R López-Valbuena, M Tena
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    ABSTRACT: Phenylalanine ammonia-lyase (PAL) from sunflower hypocotyls has been partially purified by selective precipitation with ammonium sulfate and molecular gel filtration on Sephacryl S-300. Kinetic assays carried out with this partially purified PAL preparation revealed that the enzyme did not show a homogeneous kinetic behaviour. The observed kinetic pattern and parameters (Km and Vmax) depended on the assay conditions used and the protein concentration added to the assay mixture. PAL displayed Michaelian or negative cooperativity kinetics. Such behaviour can be explained by the existence of an association-dissociation process of PAL-protein subunits. The presence of mono-, tri- and tetrameric forms of PAL has been assessed by molecular gel filtration on Sephacryl S-200, using different elution conditions.
    Biochemistry international 06/1991; 24(1):1-11.
  • Jesús Jorrin, Rafael López-Valbuena, Manuel Tena
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    ABSTRACT: Light/sucrose treatment of sunflower hypocotyls originated cyclic changes of PAL activity with alternative periods of increase and decrease of activity and maxima at 4 and 28 h (Tens et al., 1984). Actinomycin D, cordycepin and cycloheximide inhibited both induction and decay of PAL activity. These results suggest that the turnover mechanism of PAL implicates de novo synthesis of the enzyme, better than activation of inactive precursors, in response to the inducer agent (light and sucrose), and subsequent synthesis of a putative proteinaceous PAL-inactivating system responsible for PAL activity decay.
    Journal of Plant Physiology 12/1990; 137(2):252–255. · 2.77 Impact Factor
  • Jesús Jorrín, Rafael López-Valbuena, Manuel Tena
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    ABSTRACT: Trans-cinnamic acid and other metabolites of the phenylpropanoid pathway, namely p-coumaric, caffeic, ferulic and sinapic acids, inhibited the increase in extractable phenylalanine ammonia-lyase (PAL) activity present in sunflower hypocotyls in response to light-sucrose and excision-light-sucrose treatments. Otherwise, in vitro inhibitors of PAL activity, such as D-phenylalanine, and 2-aminooxyacetic and phenylpropiolic acids, superinduced extractable PAL activity and prevented the enzyme activity decay typically observed in the light-sucrose induction system. In both inducing treatments, delayed transfer of hypocotyl tissue to t-cinnamic acid caused a rapid decline in PAL activity, while a superinduction effect was observed upon transfer of the tissue to phenylpropiolic acid. These results indicate that in sunflower hypocotyls cinnamic acid(s) could act as in vivo modulator(s) of PAL, affecting the mechanisms responsible for both the increase and decrease in enzyme activity.
    Journal of Plant Physiology. 07/1990; 136(4):415–420.
  • Rafael López-Valbuena, Jesús Jorrín, Asunción Polanco, Manuel Tena
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    ABSTRACT: Two soluble forms of α-mannosidase (I and II) were purified approximately 1000-fold to electrophoretic homogeneity from sunflower hypocotyls by a procedure involving ammonium sulfate fractionation, gel filtration and anion-exchange chromatographies, and chromatofocusing. A minute amount (approximately 5% of the total purified α-mannosidase activity) of a possible third form was also detected upon chromatofocusing and was not further studied. The main I and II forms were characterized and showed the following properties: (1) glycoprotein nature; (2) apparent molecular weight of 260 000 (gel filtration); (3) pH optimum of 4.4 and isoelectric points of 4.7 (I) and 5.3 (II); (4) temperature optimum of approximately 50 °C and apparent activation energies of 32 kJ/mol (I) and 38 kJ/mol (II); (5) absolute Zn2+ requirement for activity; (6) Km and Vm values of 3.7 mM and 3.3 μkat/mg protein (I), and 2.7 mM and 3.7 μkat/mg protein (II).
    Plant Science 01/1989; · 4.11 Impact Factor
  • Jesús Jorrín, Rafael López-Valbuena, Manuel Tena
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    ABSTRACT: Phenylalanine ammonia-lyase (EC 4.3.1.5) has been purified to electrophoretic homogeneity from sucrose/ light-treated sunflower hypocotyls. The enzyme is a tetramer (molecular weight of about 250 000) composed of two pairs of subunits of different size (molecular weight of 58 000 and 68 000, respectively). Sunflower phenulalanine ammonia-lyase lacked tyrosine ammonia-lyase activity, had a pH optimum of 8.8 and an isolectric point of 4.8. The slope of the Arrhenius plot showed a discontinuity at 35°C and the values above and below the transition temperature were 32 and 55 kJ · mol−1, respectively. Phenylalanine ammonia-lyase activity was strongly inactivated by some heavy metal ions and by the amino group reagent acetic anhydride, but was latter effect was completely prevented by the simultaneous presence of substrate. Sulfhydryl group reagents produced slight inactivation, whereas carbonyl group reagents had no detrimental effects on enzyme activity. Although the enzyme showed normal Michaelian kinetics (Km and Vmax of 0.27 mM and 4.37 nkat · (mg protein)−1, respectively), a slight negative cooperativity (Hill coefficient of 0.91) was observed when the assay was carried out in the presence of 10% ethylene glycol. The properties of partially purified phenylalanine ammonia-lyase from intact or cut-injured sunflower hypocotyls did not differ from those of the enzyme induced by sucrose/light.
    Biochimica et Biophysica Acta (BBA) - General Subjects 01/1988; 964(1):73–82. · 3.83 Impact Factor