Parasitism of spores of the vesicular-arbuscular mycorrhizal fungus, Glomus dimorphicum

Nous avons examiné des spores parasitées du Glomus dimorphicum. Les microscopies photonique et électronique ont révélé des perforations d'environ 0,25 à 1,0 µm de diamètre dans la paroi de la spore. La présence de papilles, réponse dynamique de l'hôte, suggère que le parasitisme se produit pendant que le champignon mycorhizien à vésicule et arbuscule est encore vivant. Aucune structure filamenteuse n'a été détectée dans les spores; cependant, des kystes d'organismes ressemblant à des amibes ont été trouvés dans les spores et ont aussi été observés en milieu gélose sur lequel ont été placées des spores du G. dimorphicum stérilisées en surface mais contenant de tels organismes. Il est postulé qu’un organisme ressemblant à une amibe était le parasite, puisque les perforations de la paroi de la spore étaient minuscules et qu'aucun champignon ou bactérie n'a été détecté dans les spores.Spores of Glomus dimorphicum were examined for parasitism. Light and scanning electron microscopy revealed perforations, approximately 0.25 to 1.0 µm in diameter, in the spore wall. The presence of papillae, a dynamic host response, suggested that the parasitism occurred while the vesicular-arbuscular mycorrhizal fungus was still alive. No filamentous structures were detected in the spores; however, cysts of amoeba-like organisms were found in the spores and were also observed on agar plates on which surface-sterilized spores of G. dimorphicum containing such organisms were placed. It is postulated that an amoeba-like organism was the parasite, since the perforations on the spore wall were minute and no bacteria or fungi were seen inside the spores

Decomposition of canola stubble by solid-state fermentation with Cyathus olla

Le Cyathus olla est étudié pour sa valeur comme inoculant pour accélérer la décomposition du chaume de canola, et ainsi réduire, dans cette culture, la fréquence des maladies véhiculées par le chaume. Le chaume envahi par le C. olla devient mou et macéré, mais l'importance de la décomposition induite par ce champignon est inconnue. La composition de la fibre du chaume de cinq cultivars de canola a été déterminée par la méthode de caractérisation des fibres de Goering Van Soest. Du substrat stérile de canola (cv. Cyclone) a été inoculé avec le C. olla et incubé à 25 C durant 45 jours avant que les fibres ne soient analysées pour détecter des modifications dans leur composition. Tous les cultivars variaient quant à la composition de la paroi cellulaire. Après incubation, le substrat de canola inoculé avec le C. olla f. brodiensis avait conservé 60,6 % de la lignine de départ, par rapport à 65,9 % pour le substrat incubé avec le C. olla f. olla et 71,8 % avec le C. olla f. anglicus. Le contenu en hémicellulose a été réduit puisque seulement 75,3, 78,6, et 81,6 % du contenu d'origine en hémicellulose a persisté après incubation avec respectivement le C. olla f. brodiensis, le C. olla f. olla, et le C. olla f. anglicus. La cellulose a aussi été dégradée, et la fraction soluble avec un détergent neutre a augmenté. Le Cyathus olla a été capable de dégrader la lignine in vitro, mais des essais au champ doivent maintenant être entrepris pour évaluer son activité de décomposition en conditions naturelles.Cyathus olla is being studied for its potential as an inoculant to accelerate decomposition of canola stubble, and hence to reduce the incidence of stubble-borne diseases of this crop. Stubble infested by C. olla appears soft and macerated, but the extent of decomposition incited by this fungus is not known. Composition of stubble fiber of five canola cultivars was determined with the Goering Van Soest method of fiber determination. Sterile canola (cv. Cyclone) substrate was inoculated with C. olla and incubated at 25 C for 45 days, followed by fiber analyses to detect changes in the fiber content. All cultivars were variable with respect to cell wall composition. Canola substrate inoculated with C. olla f. brodiensis had 60.6% of the original lignin remaining after incubation, compared to 65.9% for the substrate incubated with C. olla f. olla and 71.8% with C. olla f. anglicus. Hemicellulose content was reduced as only 75.3, 78.6, and 81.6% of the original hemicellulose content remained after incubation with C. olla f. brodiensis, C. olla f. olla, and C. olla f. anglicus, respectively. Cellulose was also degraded, and the neutral detergent soluble fraction increased. Cyathus olla was capable of degrading lignin in vitro, but field testing must follow to assess its decomposing activity under natural conditions

Phytoalexins produced in the leaves of Capsella bursa-pastoris (shepherd’s purse)

Trois phytoalexines, à savoir la camalexine (C11H8N2S), la 6-méthoxycamalexine (C12H10N2SO) et la N-méthylcamalexine (C12H10N2S) furent isolées de la bourse-à-pasteur (Capsella bursa-pastoris) après une exposition à l’ Alternaria brassicae. La N-méthylcamalexine n'avait pas été rapportée précédemment. La production de phytoalexines chez la bourse-à-pasteur est reliée à sa résistance à l’A. brassicae, un agent pathogène causant, chez les crucifères cultivées, une maladie importante à plusieurs endroits dans le monde.Three phytoalexins, camalexin (C11H8N2S), 6-methoxycamalexin (C12H10N2SO), and N-methylcamalexin (C12H10N2S), were isolated from shepherd's purse (Capsella bursa-pastoris) challenged by Alternaria brassicae. N-methylcamalexin has not been reported previously. Phytoalexin elicitation in shepherd's purse is associated with its resistance to A. brassicae, a pathogen which causes an important disease of cruciferous crops in many parts of the world

A note on phytotoxicity of homodestruxin B – a compound produced by Alternaria brassicae

L'homodestruxine B, un composé produit par l’Alternaria brassicae, agent pathogène de la tache noire du colza, est reconnue pour sa phytotoxicité envers les feuilles du Brassica napus. Nous avons trouvé que sa phytotoxicité était comparable à celle de la destruxine B, une autre toxine produite par l'agent pathogène lorsque vérifié sur le B. napus. L'homodestruxine B a causé des symptômes de diverses gravités sur les feuilles de plusieurs plantes non-hôtes. Ceci suggère que l'homodestruxine B est une toxine non-spécifique à une plante-hôte.Homodestruxin B, a compound produced by Alternaria brassicae, the causal organism of the blackspot disease of rapeseed, is known to be phytotoxic to the leaves of Brassica napus. In this study we found that its phytotoxicity was comparable to that of destruxin B, another toxin produced by the pathogen when tested on B. napus. Homodestruxin B caused symptoms of different severities in leaves of various non-host plants. The results suggestthat homodestruxin B is a non-host-specific toxin

Enzymatic activity of Cyathus olla during solid state fermentation of canola roots

Le Cyathus olla, une nidulaire, est étudié comme agent de lutte biologique contre les maladies du canola véhiculées par le chaume. Dans cette étude, notre but est de détecter et d'identifier des enzymes produites par le C. olla lors de la fermentation, en milieu solide, de racines de canola et capables de dégrader les parois cellulaires de plantes. Nous avons trouvé des activités laccase et manganèse peroxydase après 1 et 4 semaines d'incubation, et une activité aryl alcool oxydase après 4 semaines d'incubation. Des extraits bruts dans du tampon ont été testés pour la présence de cellulases et de polygalacturonase, mais seulement la polygalacturonase a été détectée. Nous en concluons que le C. olla possède des enzymes pour dégrader la lignine et qu'il pourrait être utilisé comme inoculant pour accélérer la décomposition du chaume.Cyathus olla, a bird's nest fungus, is being studied as a biological control agent of stubble-borne diseases of canola. Our objectives in this study were to detect and identify plant cell wall degrading enzymes produced by C. olla during solid state fermentation of canola roots. We identified laccase and manganese peroxidase in both 1- and 4-week incubations, and aryl-alcohol oxidase was detected following 4 weeks of incubation. Crude buffer extracts were assayed for cellulases and polygalacturonase, but only the latter was detected. We conclude that C. olla has enzymes to degrade lignin and that it may have use as an inoculant to accelerate stubble decomposition

Assessment of Two Different Sources of Durable Resistance and Susceptible Cultivar of Wheat to Stripe Rust (Puccinia striiformis f. sp. tritici)

A study was conducted to assess the durable resistance in a near isogenic line of spring wheat (Triticum aestivalis L.), possessing resistance gene Yr-18 to some isolates (race specific resistance) of stripe rust (Puccinia striiformis f. sp. tritici), namely Thatcher Yr-18 and durable resistance of an cultivar of spring wheat to all isolates of stripe rust (race non- specific resistance), namely Hybrid de Berse'e. In this investigation fresh urediniospores of two isolates namely SRC 99 (race 70E 128) and SRC 89 (race 14E 14), were collected from a susceptible cultivar of spring wheat, Avocet, as inoculums. Then suspension of spore in mineral oil [Soltrol 170 (5 mg/ml)] were sprayed on third and flag leaves of the booth genotypes mentioned above and on the Thatcher cultivar which was susceptible to booth isolates. The Percentage of urediniospore germination, latent period and infection types of all susceptible and resistant genotypes to booth isolates were determined in four replicates at seedling and adult plant stages. Mean percentage of spore germination and the value of latent period were analyzed separately in each replicate, and then compared using analysis of variance and the Student- Newman Keuls test. The results indicated that urediniospoe germination in all genotypes / isolates/ leaf stage combination was high and neither resistance type affected spore germination significantly. In both types of resistance, latent period increased with advancing plant age. In general cultivars possessing resistant gene had longer latent periods. Assessment of the infection type showed that, the durable resistance of Hybrid de Bers?e is detected at an earlier stage than the adult-plant resistance of near isogenic line containing the gene Yr18

Optical Sum Rule in Finite Bands

In a single finite electronic band the total optical spectral weight or optical sum carries information on the interactions involved between the charge carriers as well as on their band structure. It varies with temperature as well as with impurity scattering. The single band optical sum also bears some relationship to the charge carrier kinetic energy and, thus, can potentially provide useful information, particularly on its change as the charge carriers go from normal to superconducting state. Here we review the considerable advances that have recently been made in the context of high $T_c$ oxides, both theoretical and experimental.Comment: Review article accepted for publication in J. Low Temp. Phys. 29 pages, 33 figure

Genome-wide functional analysis reveals key roles for kinesins in the mammalian and mosquito stages of the malaria parasite life cycle

Kinesins are microtubule (MT)-based motors important in cell division, motility, polarity, and intracellular transport in many eukaryotes. However, they are poorly studied in the divergent eukaryotic pathogens Plasmodium spp., the causative agents of malaria, which manifest atypical aspects of cell division and plasticity of morphology throughout the life cycle in both mammalian and mosquito hosts. Here, we describe a genome-wide screen of Plasmodium kinesins, revealing diverse subcellular locations and functions in spindle assembly, axoneme formation, and cell morphology. Surprisingly, only kinesin-13 is essential for growth in the mammalian host while the other 8 kinesins are required during the proliferative and invasive stages of parasite transmission through the mosquito vector. In-depth analyses of kinesin-13 and kinesin-20 revealed functions in MT dynamics during apical cell polarity formation, spindle assembly, and axoneme biogenesis. These findings help us to understand the importance of MT motors and may be exploited to discover new therapeutic interventions against malaria

Kinesin-8B controls basal body function and flagellum formation and is key to malaria transmission

Eukaryotic flagella are conserved microtubule-based organelles that drive cell motility. Plasmodium, the causative agent of malaria, has a single flagellate stage: the male gamete in the mosquito. Three rounds of endomitotic division in male gametocyte together with an unusual mode of flagellum assembly rapidly produce eight motile gametes. These processes are tightly coordinated, but their regulation is poorly understood. To understand this important developmental stage, we studied the function and location of the microtubule-based motor kinesin-8B, using gene-targeting, electron microscopy, and live cell imaging. Deletion of the kinesin-8B gene showed no effect on mitosis but disrupted 9+2 axoneme assembly and flagellum formation during male gamete development and also completely ablated parasite transmission. Live cell imaging showed that kinesin-8B–GFP did not co-localise with kinetochores in the nucleus but instead revealed a dynamic, cytoplasmic localisation with the basal bodies and the assembling axoneme during flagellum formation. We, thus, uncovered an unexpected role for kinesin-8B in parasite flagellum formation that is vital for the parasite life cycle

Author Correction:Plasmodium APC3 mediates chromosome condensation and cytokinesis during atypical mitosis in male gametogenesis

Host-parasite interactio