Compatible interactions between male gametophytes (pollen) and the female reproductive organ (pistil) are essential for fertilization in flowering plants. Recognition at a molecular level allows “compatible” pollen grains to adhere/germinate on the stigma while pollen grains from unrelated plant species are largely ignored. The exocyst is a large eight subunit complex that is primarily involved in polarized secretion or regulated exocytosis in eukaryotic cells where it functions to tether vesicles to the plasma membrane. Recent research has implicated one of the Exo70 family members, Exo70A1, in compatible pollen-pistil interactions in Arabidopsis and Brassica. The loss of Exo70A1 in Arabidopsis Col-0 stigmas leads to the rejection of compatible pollen producing a “female sterile” phenotype. Through my research I have demonstrated that, driven by a stigma-specific promoter, an RFP:Exo70A1 fusion protein rescues this defect in exo70A1-1 mutant and Exo70A1 is found to be localized to the plasma membrane at flower opening.

The phytopathogenic fungus <i>Leptosphaeria maculans</i> can cause blackleg disease on crucifers, which results in significant yield losses. Fungal diseases involve interactions between pathogenic fungi and host plants. One aspect of these interactions is mediated by secondary metabolites produced by both fungi and host plants. Phytotoxins and elicitors as well as phytoanticipins and phytoalexins are metabolites produced by fungi and plants, respectively. This thesis describes and discusses the isolation, structure, biological activity and biosynthesis of the secondary metabolites produced by L. maculans.<p> The elicitor-toxin activity bioassay guided isolation of elicitors and phytotoxins produced by <i>L. maculans</i> in a chemically defined medium lead to the isolation of general elicitors, <i>sirodesmin PL</i> (165) and <i>deacetylsirodesmin PL</i> (166), and specific elicitors, <i>cerebrosides C</i> (14) and D (31) from minimum medium (MM) culture under standard conditions. The known phytotoxins sirodesmin PL (165) and deacetylsirodesmin PL (166) induced the production of <i>phytoalexin spirobrassinin</i> (122) in both resistant plant species (brown mustard, <i>Brassica juncea</i> cv. Cutlass) and susceptible plant species (canola, B. napus cv. Westar). A mixture of cerebrosides C (14) and D (31) induced the production of the phytoalexin rutalexin (127) in resistant plant species (brown mustard, B. juncea cv. Cutlass) but not in susceptible plant species (canola, B. napus cv. Westar). New metabolites leptomaculins A-E (267-269, 272 and 274) and deacetylleptomaculins C-E (270, 273 and 275) were isolated from elicitor-phytotoxin active fractions but did not display detectable elicitor activity or phytotoxicity after purification.<p> New metabolites maculansins A (299) and B (300), which were not detected in cultures of L. maculans incubated in MM, were isolated from cultures of <i>L. maculans</i> incubated in potato dextrose broth (PDB). Maculansins A (299) and B (300) displayed higher phytotoxicity on brown mustard than on canola and white mustard (<i>Sinapis alba cv. Ochre</i>) but did not elicit detectable production of phytoalexins in either brown mustard or canola. Metabolite 2,4-dihydroxy-3,6-dimethylbenzaldehyde (212) was produced in higher amount in cultures of L. maculans incubated in PDB than in MM and displayed strong inhibition effect on the root growth of brown mustard and canola. <i>L. maculans</i> incubated in MM amended with high concentration of NaCl produced a new metabolite, 8-hydroxynaphthalene-1-sulfate (293), and a known metabolite, bulgarein (294), which are likely involved in the self-protection. The potential intermediates involved in the biosynthesis of sirodesmin PL (165) were investigated using deuterium labeled precursors: [3,3-2H2]-L-tyrosine (251a), [3,3-2H2]O-prenyl-L-tyrosine (312a), E-[3,3,5,5,5-2H5]O-prenyl-L-tyrosine (312b), [5,5-2H2]phomamide (171a), [2,3,3-2H3]-L-serine (233d) and [5,5-2H2]cyclo-L-tyr-L-ser (252a). Intact incorporation of [5,5-2H2]phomamide (171a) into sirodesmin PL (165) suggested that leptomaculin D (272) and E (274), and deacetylleptomaculin D (273) and E (275) are not intermediates in the biosynthesis of sirodesmin PL (165). They are more likely the catabolic metabolites of sirodesmin PL (165). Phomamide (171), the intermediate in the biosynthetic pathway of sirodesmin PL (165), is likely biosynthesized by coupling of prenyl tyrosine (312) with serine (233) rather than prenylation of cyclo-L-tyr-L-ser (252). When [3,3-2H2]-L-tyrosine (251a), [3,3-2H2]O-prenyl-L-tyrosine (312a), and E-[3,3,5,5,5-2H5]O-prenyl-L-tyrosine (312b) were fed into cultures of L. maculans, a â proton exchange was detected by 1H NMR through intrinsic steric isotope effect, which occurs before the formation of phomamide (171). The biosynthesis and catabolism of sirodesmin PL (165) were proposed based on the results obtained in this work.

Investigations into the biology and control of the annual grassy weed Bromus pectinatus Thunb. were conducted at the National Plant Breeding Station, Njoro, Kenya, from 1982 to 1984. Pot growth of B. pectinatus was influenced by soil type and microclimate, but not by seed origin. B. pectinatus was germinated and grown in amended and untreated soils ranging in pH from 3.05 to 8.13. Soils with a pH near 3 could not support growth or germination of B. pectinatus. B. pectinatus grew best on a soil of pH 6.55 and when soil pH influenced germination the optimum soil pH was 6.0. Exposure to light inhibited the germination of B. pectinatus seeds. Germination of B. pectinatus seed was most rapid at a 17 C temperature. Germination of dormant B. pectinatus seeds was enhanced by seed hull removal or pricking the lemma or removing the rachilla segment. Germination of B. pectinatus seed in the soil was unaffected by depth of burial, whereas, emergence was reduced to 35, 19, 11, 4 and 0% from depths of 0, 1, 2, 4 and 8 cm, respectively. There was a relationship between field emergence of B. pectinatus and the precipitation pattern. After-harvest germination of B. pectinatus seed indicated that there was an innate dormancy in hulled seed which persisted for 8 months. Field measurements were used to develop an equation which related yield loss in wheat with B, pectinatus infestation. Delayed sowing of wheat and barley into a B. pectinatus infested site resulted in yield reductions that were correlated with length of delay. Replacement series studies were conducted using varying proportions of wheat : B. pectinatus and rapeseed : B. pectinatus. Rapeseed / canola was unaffected by B. pectinatus interference. A spatial interference study determined that B. pectinatus interfers with wheat mainly above ground. The herbicides isoproturon, pendimethalin and oxadiazon were found to be ineffective against B. pectinatus, The herbicides triallate, chlorsulfuron, metribuzin, trifluralin and EPTC achieved limited control of B, pectinatus. Superior control of B. pectinatus was achieved using fluazifop-butyl at 0.25 kg/ha and fenthiaprop-ethyl at 0.12 kg/ha, in rapeseed / canola. / May 1986

The phytopathogenic fungus <i>Leptosphaeria maculans</i> can cause blackleg disease on crucifers, which results in significant yield losses. Fungal diseases involve interactions between pathogenic fungi and host plants. One aspect of these interactions is mediated by secondary metabolites produced by both fungi and host plants. Phytotoxins and elicitors as well as phytoanticipins and phytoalexins are metabolites produced by fungi and plants, respectively. This thesis describes and discusses the isolation, structure, biological activity and biosynthesis of the secondary metabolites produced by L. maculans.<p> The elicitor-toxin activity bioassay guided isolation of elicitors and phytotoxins produced by <i>L. maculans</i> in a chemically defined medium lead to the isolation of general elicitors, <i>sirodesmin PL</i> (165) and <i>deacetylsirodesmin PL</i> (166), and specific elicitors, <i>cerebrosides C</i> (14) and D (31) from minimum medium (MM) culture under standard conditions. The known phytotoxins sirodesmin PL (165) and deacetylsirodesmin PL (166) induced the production of <i>phytoalexin spirobrassinin</i> (122) in both resistant plant species (brown mustard, <i>Brassica juncea</i> cv. Cutlass) and susceptible plant species (canola, B. napus cv. Westar). A mixture of cerebrosides C (14) and D (31) induced the production of the phytoalexin rutalexin (127) in resistant plant species (brown mustard, B. juncea cv. Cutlass) but not in susceptible plant species (canola, B. napus cv. Westar). New metabolites leptomaculins A-E (267-269, 272 and 274) and deacetylleptomaculins C-E (270, 273 and 275) were isolated from elicitor-phytotoxin active fractions but did not display detectable elicitor activity or phytotoxicity after purification.<p> New metabolites maculansins A (299) and B (300), which were not detected in cultures of L. maculans incubated in MM, were isolated from cultures of <i>L. maculans</i> incubated in potato dextrose broth (PDB). Maculansins A (299) and B (300) displayed higher phytotoxicity on brown mustard than on canola and white mustard (<i>Sinapis alba cv. Ochre</i>) but did not elicit detectable production of phytoalexins in either brown mustard or canola. Metabolite 2,4-dihydroxy-3,6-dimethylbenzaldehyde (212) was produced in higher amount in cultures of L. maculans incubated in PDB than in MM and displayed strong inhibition effect on the root growth of brown mustard and canola. <i>L. maculans</i> incubated in MM amended with high concentration of NaCl produced a new metabolite, 8-hydroxynaphthalene-1-sulfate (293), and a known metabolite, bulgarein (294), which are likely involved in the self-protection. The potential intermediates involved in the biosynthesis of sirodesmin PL (165) were investigated using deuterium labeled precursors: [3,3-2H2]-L-tyrosine (251a), [3,3-2H2]O-prenyl-L-tyrosine (312a), E-[3,3,5,5,5-2H5]O-prenyl-L-tyrosine (312b), [5,5-2H2]phomamide (171a), [2,3,3-2H3]-L-serine (233d) and [5,5-2H2]cyclo-L-tyr-L-ser (252a). Intact incorporation of [5,5-2H2]phomamide (171a) into sirodesmin PL (165) suggested that leptomaculin D (272) and E (274), and deacetylleptomaculin D (273) and E (275) are not intermediates in the biosynthesis of sirodesmin PL (165). They are more likely the catabolic metabolites of sirodesmin PL (165). Phomamide (171), the intermediate in the biosynthetic pathway of sirodesmin PL (165), is likely biosynthesized by coupling of prenyl tyrosine (312) with serine (233) rather than prenylation of cyclo-L-tyr-L-ser (252). When [3,3-2H2]-L-tyrosine (251a), [3,3-2H2]O-prenyl-L-tyrosine (312a), and E-[3,3,5,5,5-2H5]O-prenyl-L-tyrosine (312b) were fed into cultures of L. maculans, a â proton exchange was detected by 1H NMR through intrinsic steric isotope effect, which occurs before the formation of phomamide (171). The biosynthesis and catabolism of sirodesmin PL (165) were proposed based on the results obtained in this work.

Ph.d.-afhandling. Den Kongelige Veterinær- og Landbohøjskole, 2002. / Haves også i trykt udg.

No description available.

Investigations into the biology and control of the annual grassy weed Bromus pectinatus Thunb. were conducted at the National Plant Breeding Station, Njoro, Kenya, from 1982 to 1984. Pot growth of B. pectinatus was influenced by soil type and microclimate, but not by seed origin. B. pectinatus was germinated and grown in amended and untreated soils ranging in pH from 3.05 to 8.13. Soils with a pH near 3 could not support growth or germination of B. pectinatus. B. pectinatus grew best on a soil of pH 6.55 and when soil pH influenced germination the optimum soil pH was 6.0. Exposure to light inhibited the germination of B. pectinatus seeds. Germination of B. pectinatus seed was most rapid at a 17 C temperature. Germination of dormant B. pectinatus seeds was enhanced by seed hull removal or pricking the lemma or removing the rachilla segment. Germination of B. pectinatus seed in the soil was unaffected by depth of burial, whereas, emergence was reduced to 35, 19, 11, 4 and 0% from depths of 0, 1, 2, 4 and 8 cm, respectively. There was a relationship between field emergence of B. pectinatus and the precipitation pattern. After-harvest germination of B. pectinatus seed indicated that there was an innate dormancy in hulled seed which persisted for 8 months. Field measurements were used to develop an equation which related yield loss in wheat with B, pectinatus infestation. Delayed sowing of wheat and barley into a B. pectinatus infested site resulted in yield reductions that were correlated with length of delay. Replacement series studies were conducted using varying proportions of wheat : B. pectinatus and rapeseed : B. pectinatus. Rapeseed / canola was unaffected by B. pectinatus interference. A spatial interference study determined that B. pectinatus interfers with wheat mainly above ground. The herbicides isoproturon, pendimethalin and oxadiazon were found to be ineffective against B. pectinatus, The herbicides triallate, chlorsulfuron, metribuzin, trifluralin and EPTC achieved limited control of B, pectinatus. Superior control of B. pectinatus was achieved using fluazifop-butyl at 0.25 kg/ha and fenthiaprop-ethyl at 0.12 kg/ha, in rapeseed / canola.

Les agroécosystèmes sont des mosaïques d'espaces cultivés, d'espaces naturels et semi-naturels et d'infrastructures humaines fortement imbriqués et donc intrinsèquement liés et dépendants. Les espaces semi-naturels sont confinés généralement aux bordures de champs et aux bordures de route où se côtoient biodiversités végétales cultivées et sauvages. Cette thèse se concentre principalement sur la dispersion des graines de colza (Brassica napus L.) vers ces espaces qui peut conduire à la formation de populations de colza dites férales. A l'échelle d'un agroécosystème, l'étude de données génotypiques couplées à des méthodes d'assignations aux variétés commerciales existantes, a permis de mettre en évidence un lien entre la diversité variétale des champs de colza cultivés et la diversité variétale des populations férales de l'année suivante. De surcroît, l'étude de ces diversités variétales a montré que les champs ne sont pas des entités uniformes comportant des plantes d'une seule variété et que les populations férales accumulent les variétés au fil des années grâce aux apports annuels des champs récoltés, à la survie dans la banque de graines et à l'autorecrutement au sein des populations férales. La modélisation des flux efficaces de graines par une méthode de maximum de vraisemblance a permis d'identifier des dynamiques de dispersion locales au sein des agroécosystèmes. Suivant la zone considérée et les axes de circulation vers le silo de récolte, les sources locales de graines varient et les apports extérieurs de graines sont plus ou moins importants. Nos données nous ont permis d'estimer que les semis de la même année (n), les champs récoltés l'année antérieure ou même les années précédentes (jusqu'à n-2) pouvaient contribuer de manière significative à la présence de populations férales (l'année n). Les distances moyennes de dispersion estimées varient de la dizaine de mètres au kilomètre. Enfin, une expérimentation in-situ nous a permis de quantifier les pertes de graines pendant la récolte liées aux bennes de récolte. Nous avons évalué ces pertes à 400 graines par m2 et nous avons mis en évidence de rares évènements de pertes massives de graines. L'analyse statistique des résultats de ces pertes nous a permis de les mettre en relation avec des caractéristiques du paysage, notamment les surfaces des champs et les axes de circulations principaux et secondaires. Dans le contexte de mise en culture de plantes transgéniques, ces résultats impliquent de prendre en compte la complexité du paysage dans les modèles qui prédisent les flux de transgènes à l'échelle des agroécosystèmes.

Investigations into the biology and control of the annual grassy weed Bromus pectinatus Thunb. were conducted at the National Plant Breeding Station, Njoro, Kenya, from 1982 to 1984. Pot growth of B. pectinatus was influenced by soil type and microclimate, but not by seed origin. B. pectinatus was germinated and grown in amended and untreated soils ranging in pH from 3.05 to 8.13. Soils with a pH near 3 could not support growth or germination of B. pectinatus. B. pectinatus grew best on a soil of pH 6.55 and when soil pH influenced germination the optimum soil pH was 6.0. Exposure to light inhibited the germination of B. pectinatus seeds. Germination of B. pectinatus seed was most rapid at a 17 C temperature. Germination of dormant B. pectinatus seeds was enhanced by seed hull removal or pricking the lemma or removing the rachilla segment. Germination of B. pectinatus seed in the soil was unaffected by depth of burial, whereas, emergence was reduced to 35, 19, 11, 4 and 0% from depths of 0, 1, 2, 4 and 8 cm, respectively. There was a relationship between field emergence of B. pectinatus and the precipitation pattern. After-harvest germination of B. pectinatus seed indicated that there was an innate dormancy in hulled seed which persisted for 8 months. Field measurements were used to develop an equation which related yield loss in wheat with B, pectinatus infestation. Delayed sowing of wheat and barley into a B. pectinatus infested site resulted in yield reductions that were correlated with length of delay. Replacement series studies were conducted using varying proportions of wheat : B. pectinatus and rapeseed : B. pectinatus. Rapeseed / canola was unaffected by B. pectinatus interference. A spatial interference study determined that B. pectinatus interfers with wheat mainly above ground. The herbicides isoproturon, pendimethalin and oxadiazon were found to be ineffective against B. pectinatus, The herbicides triallate, chlorsulfuron, metribuzin, trifluralin and EPTC achieved limited control of B, pectinatus. Superior control of B. pectinatus was achieved using fluazifop-butyl at 0.25 kg/ha and fenthiaprop-ethyl at 0.12 kg/ha, in rapeseed / canola.

The effects of nitrogen and sulfur fertilization on the oviposition, feeding preferences, and larval performance of Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) on Brassica napus L. were examined in a series of laboratory experiments. The associations between C. obstrictus adults, larvae and parasitoids, and environmental factors including plant vigor indicators and soil and plant nutrients were evaluated within two commercial fields of B. napus in southern Alberta. Nitrogen fertilization, and sulfur fertilization at low levels of nitrogen fertilization had positive effects on oviposition preference. Nitrogen had a positive effect on larval development times and no effect on larval weights. Within one field, gravid C. obstrictus females were dissociated with high levels of plant nutrients including nitrogen. The synthesis of the lab and field experiments seems to support the plant stress and the preference-performance hypotheses. Differences in olfactory and visual cues are identified as a possible mechanism for the observed differences. / Ecology