Inaug.-Diss.--Erlangen. / Lebenslauf.

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 133-145). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2011. / Printout. Includes bibliographical references (leaves 116-136). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 47-54). Also available on the World Wide Web.

Thesis (M.Sc.(Plant Protection)) -- University of Limpopo, 2022 / Runner beans are extremely sensitive to root-knot (Meloidogyne species) nematodes. Phytonematicides had been consistently used in managing population densities of Meloidogyne species in various crops, with the application technologies being restricted to the ground leaching technology (GLT) and botinemagation technology, each with its own advantages and disadvantages. The use of seeds as carriers of active ingredients of phytonematicides and then drying prior to sowing, is being considered as another potential application strategy in seeds with hypogeal germination. In such seeds, during seedling emergence the seed cover and the endosperm remain below the soil surface, just above the developing root system. As a result, in phytonematicide-primed seeds, the seed structures could serve as carriers for the active ingredients of phytonematicides. In cucurbitacin phytonematicides, Nemarioc-AL and Nemafric-BL phytonematicides contain cucurbitacin A and B, respectively as active ingredients. The objectives of the study were two-fold, namely, to determine whether runner bean (Phaseolus coccineus L.) seeds would (1) serve as carriers of active ingredients of cucurbitacin-containing phytonematicides without affecting seed germination under in vitro conditions, (2) serve as carriers of cucurbitacins intended for suppression of M. incognita population densities under greenhouse and microplot conditions. Two separate studies were conducted under laboratory conditions, with seven treatment solutions at 0, 2, 4, 8, 16, 32 and 64% Nemafric-BL or Nemarioc-AL phytonematicide. After exposure to separate solutions for 2 h, runner bean seeds were dried on laboratory benches for 72 h. Treatments were arranged in a completely randomised design (CRD), with 8 replications. Two layers of filter papers were placed inside each Petri dish seeded with 10 primed and dried seeds. Petri dishes were incubated inside LABCON growth chamber at 25ºC and 75% relative humidity. Successful seed germination, viewed as emergence of radicle from the testa, was recorded daily for a period of 10 days, with each count being removed from Petri dish to avoid re-counting. Under greenhouse and microplot conditions, primed-and dried seeds were sown in plastic pots containing 2 700 ml steam-pasteurised sandy loam soil, arranged in a randomised complete block design, replicated six times and eight times, respectively. Each seedling was inoculated by distributing 5 000 eggs and second-stage juveniles (J2) of M. incognita race 4 using a 50 ml plastic syringe. Originally, pots were irrigated using 500 ml chlorine-free tapwater, which was reduced to half after seedling emergence at every other day. Plant variables were collected at 56 days after inoculation and data were subjected to the Curve-fitting Allelochemical Response Dose algorithm model. In vitro, germination percentage (R 2 = 0.96), radicle length (R 2 = 0.89) and plumule diameter (R 2 = 0.96) versus Nemarioc-AL phytonematicide exhibited positive quadratic relations. Similarly, the variables versus Nemafric-BL phytonematicide, exhibited positive quadratic relations. In vitro, Mean Concentration Stimulation Point (MCSP) value of Nemarioc-AL phytonematicide on runner bean seeds was 1.05%, whereas for Nemafric-BL phytonematicide MCSP value was 0.58%. Under greenhouse conditions, plant height (R 2 = 0.97), chlorophyll content (R 2 = 0.92), dry shoot mass (R 2 = 0.98), dead nodule number (R 2 = 0.90), total pod number (R 2 = 0.97) and active nodule number (R 2 = 0.93) versus Nemarioc-AL phytonematicide exhibited positive quadratic relations., Similarly, chlorophyll content (R 2 = 0.95), gall rating (R 2 = 0.82), dry shoot weight (R 2 = 0.69), stem diameter (R 2 = 0.85) and total nodule number (R 2 = 0.86) versus Nemafric-BL phytonematicide exhibited positive quadratic relations. Under greenhouse conditions, MCSP values for Nemarioc-AL and Nemafric-BL phytonematicides were 4.18 and 3.69%, respectively. Under microplot conditions, total number of nodules (R 2 = 0.88), number of nodules dead (R 2 = 0.99), number of nodules active (R 2 = 0.95), fresh root mass (R 2 = 0.99), and fresh pod mass (R 2 = 0.99) versus Nemarioc-AL phytonematicide, exhibited positive quadratic relations, whereas plant height (R 2 = 0.85), number of nodules dead (R 2 = 0.87), dry shoot mass (R 2 = 0.97), fresh root mass (R 2 = 0.97) and total number of nodules (R 2 = 0.63) versus Nemafric-BL phytonematicide exhibited positive quadratic relations. Under microplot conditions, MCSP values for Nemarioc-AL and Nemafric-BL phytonematicides were 3.76 and 3.93%, respectively, each with ∑k = 0. All degrees of Nemarioc-AL and Nemafric-BL phytonematicides profoundly reduced nematode numbers under greenhouse and microplot trials. Based on the information obtained from this study, it was confirmed that runner bean (P. coccineus) is sensitive to Nemafric-BL and Nemarioc-AL phytonematicides supported by the Curve-fitting Allelochemical Response Dose (CARD) model results due to most plant variables that had sensitivity values of zero. In conclusion, the priming technology should be developed further since it has the potential of being successful in nematode management in seeds with hypogeal germination / National Research Foundation (NRF) and Potatoes South Africa

Chez les végétaux, peu de canaux ioniques sont identifiés moléculairement. Nos travaux, par l’apport de preuves fonctionnelles, mettent en évidence les propriétés électrophysiologiques d’une protéine de la membrane mitochondriale externe (MOM) de Phaseolus coccineus, VDAC32. Nous montrons que cette protéine forme un canal partageant plusieurs caractéristiques électrophysiologiques typiques des canaux anioniques voltages dépendants (VDACs) (cinétique d'ouverture et de fermeture, sensibilité au voltage, conductance relativement grande, courbe de voltage dépendance en forme de cloche). <p>Nous avons constaté que la concentration saline avait un effet sur la voltage-dépendance du canal. En effet, le VDAC devient insensible à la différence de potentiel appliquée lorsqu'il est reconstitué dans des concentrations physiologiques en sel. Nombreuses sont les expériences réalisées dans des conditions non physiologiques (1 M KCl), mais nous montrons dans ce travail que le canal ne se comporte pas de la même manière en conditions physiologiques (0,1 M KCl).<p>La première partie de notre travail a été consacrée à l’étude de l’effet du cholestérol et deux phytostérols les plus abondants (sitostérol et stigmastérol) sur la voltage-dépendance du VDAC. Dans ce chapitre, nous avons montré l’effet des stérols sur la fonction des canaux ioniques au niveau moléculaire. Le rôle des stérols sur la sélectivité et la voltage-dépendance du VDAC a été mis en évidence. L’étude des phytostérols a permis de comprendre comment les propriétés du VDAC peuvent être modulées avec le type de stérol et son abondance dans la membrane. De même, la réversibilité de l’effet des phytostérols sur le VDAC en présence de la Méthyle-β-cyclodextrine a été prouvée. La conductance unitaire n’était pas affectée par l’addition des stérols.<p>Le deuxième chapitre de cette thèse a été consacré à l’étude des deux principaux phospholipides membranaires ;la phosphatidylcholine (PC) et phosphatidyl-éthalamine (PE). Il a été montré qu’à des concentrations salines similaires à celles trouvées in vivo, la voltage-dépendance du VDAC est inhibée en présence de membrane formée de PC mais pas en présence de membrane formée de PE et/ou PE méthylé une fois et deux fois. De même, la voltage-dépendance est restaurée suite à l’ajout de 2% de phytostérol ou de 2% de PE ou lorsque le degré de méthylation de la choline diminue. L’effet des stérols sur la voltage-dépendance est réversible. Nous avons montré que la sélectivité aux anions augment lorsque le degré de méthylation de la choline diminue tandis que la conductance unitaire du canal est invariable.<p>Nos résultats indiquent que l’interaction lipide-protéine est essentielle pour la régulation de l’activité du canal VDAC. La nature de la tête polaire des lipides est déterminante pour cette régulation ce qui suggère qu’elle s’effectue au niveau de l’interface membrane-solution. <p>La suite de nos travaux nous a conduit à l’étude de l’effet du cation monovalent, divalent et trivalent sur le VDAC. Nous avons montré que la voltage-dépendance est perdue dans des concentrations faibles en KCl (100 mM) et que cette dernière est restaurée en présence de 800 mmolale en KCl ou 100 mM de calcium ou 30 mM de lanthane. Ces résultats suggèrent que la restauration de la voltage-dépendance à des faibles concentrations en sel (100 mmolale) impliquerait un effet électrostatique/In plants, only some ion channels are identified molecularly. By providing functional evidence, our work highlights electrophysiological properties of the outer mitochondrial membrane (MOM) protein of Phaseolus coccineus, VDAC32. We show that this protein forms a channel sharing several typical electrophysiological characteristics of voltages dependent anion channels (VDACs) (gating kinetics, voltage sensitivity, relatively large conductance, voltage dependence curve bell-shaped).<p>We found that the salt concentration had an effect on the voltage-dependence of channel. Indeed, VDAC becomes insensitive to the applied potential difference when it was reconstituted in physiological salt concentrations. The greater part of the experiments were performed under non-physiological conditions (1 M KCl), but we show in our work that the channel does not have the same behavior under physiological conditions (0.1 M KCl).<p>The first part of our work has been devoted to the study of the effect of cholesterol and the two most abundant phytosterols (sitosterol and stigmasterol) on the VDAC voltage dependence. In this chapter, we have shown the effect of sterols on ion channel function at the molecular level. The role of sterols on the selectivity and the voltage-dependence of VDAC was highlighted. The study of phytosterols helped us to understand how the properties of VDAC can be modulated with the type of sterol and its abundance in the membrane. Similarly, the reversibility of the effect of phytosterols on the VDAC in the presence of Methyl-β-cyclodextrin has been proven. The unit conductance was not affected by the addition of sterols.<p>The second chapter of this thesis was devoted to the study of the two major membrane phospholipids, phosphatidylcholine (PC) and phosphatidylethalamine (PE). It has been shown that in similar salt concentrations to those found in vivo, the VDAC voltage-dependence is inhibited in the presence of membrane formed by PC but not in the presence of membrane formed by PE and/or PE methylated once and two times. Similarly, the voltage-dependence is recovered following the addition of 2% of phytosterol or 2% of PE or when the degree of methylation of choline decreases. The effect of sterols on the voltage-dependence is reversible. We have shown that the anion selectivity increases when the degree of methylation of choline decreases while the unitary conductance of the channel is invariable.<p>Our results indicate that lipid-protein interaction is essential for the regulation of the activity of VDAC channel. The nature of the lipids polar head is crucial for this regulation suggesting that it occurs at the membrane-solution interface.<p>The rest of our work has led us to study the effect of monovalent, divalent and trivalent cation on VDAC. We have shown that the voltage-dependence is lost in low concentrations of KCl (100 mM) and it is restored in the presence of 800 mmolale of KCl or 100 mM of calcium or 30 mM of lanthanum. These results suggest that the restoration of the voltage-dependence at low salt concentrations (100 mmolale) involve an electrostatic effect.<p> / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

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