Caractéristiques polliniques des plantes mellifères de la zone soudano-guinéenne d'altitude de l'ouest Cameroun

Pollen Characteristics of Melliferous Plants of the Soudano Guinean Western Highlands of Cameroon. Between November 2000 and 2001, an inventory and pollen characteristics study of major melliferous plants of the Menoua Division in the Western highlands of Cameroon (Latitude North 5° 21.45N- 5°35.44'N and Longitude east 10°04.72- 10°26.24) were carried out. A total of 78 melliferous plants belonging to 33 families were identified. In terms of number of plants, the most-represented species were Asteraceae (12.9%); Solanaceae (8.6%); Euphorbiaceae (7.6%); Myrtaceae and Malvaceae (6.4%) respectively in decreasing order. As concerns pollen characteristics inter and intra families variations were recorded. The smallest pollen size (15.7 ± 1.6 μ) was found with Leucaena leucocephala while Calliandra callothyrsus had the highest (190.9 ± 7.1 μ). Subcircular pollen form was predominant (Asteraceae 39.2% of the 78 melliferous plants) followed respectively by spheric (20.3%; Convovulaceae), elliptic (12.2%; Dacryodes edulis, cordia sp.), and triangular (10.8%; Myrtaceae). Melliferous plants with aperturated exine pollen (Ageratum conyzoides, Psidium guayava) were predominant (71.7%) compared to those without aperturated exine pollen (Manihot esculenta, Croton macrostachyus; 28.2%). Pollen ornamentation also showed a trend of variation between species. Smooth pollen plants (Arachis hypogaea, Psidium guajava) were more numerous (46.1%), followed respectively by spined (25.6%; Asteracea, Malvaceae) and scabrous pollen species (Casuarina equisetifolia, Musa paradisiaca)

Sustainable management of a natural threatened resource: The case study of Vepris heterophylla (engl.) Letouzey (rutaceae) in the Sudano-Sahelian zone of Cameroon

Useful trees are believed to be threatened. However most evidence about these concerns is anecdotal. The objectives of the study were to document uses of Vepris heterophylla (Engl.) Letouzey, management patterns, determine its population structure and assess the influence of mountain sides in the sudanosahelian zone of Cameroon. The study was carried out using ethnobotanical and quantitative ecological methods. The results showed that the species was found to be multipurpose and produced six different products and services. The most mentioned services were conservation of the foodstuffs and medicine. Community responses indicated that the species became rare and there were no strategies developed to preserve it. The quantitative inventory supported this community view: the species had a low density (28.8 individuals/ha) and a weak size class distribution with calculated least-squares regression slopes of a1=-0.435 (Sahelian section) and a2=-0.263 (Sudanian section). The opposition of the side had an influence on the population (÷2=33.15; df=9; P <0.001). The species appeared to be threatened by the overexploitation and poor attitude to its conservation. Respondents claimed that they were not interested in conserving it because they lacked propagation materials and skills. The sensitization and the domestication of the plant should be considered urgently.Keywords: Vepris heterophylla, Threatened species, Sustainable management, Sudano-sahelian zone, Opposition sides

Predominant melliferous plants of the western Sudano Guinean zone of Cameroon

Between September 2003 and March 2005, melissopalynological methods were used to access the predominant melliferous plants (PMP) in 104 honey samples collected from the Soudano Guinean highlands zone of west Cameroon. A total of 19 PMP from 11 families were identified, Asteraceae is the most represented. Trees and herbs were frequently exploited. Spontaneous PMP were more represented. Perennial PMP were highly visited by Apis mellifera adansonii. PMP with white colour flower are the most utilized by bees compared to other colours. When seasonal exploitation was considered, the proportion of PMP exploited in the rainy season was higher. Eucalyptus saligna, Terminalia mantaly and Pterocarpus soyauxii were frequently exploited.Key words: Apis mellifera adansonii, melliferous plant, predominant, harvested

Physico-chemical and microbiological characteristics of honey from the sudano-guinean zone of West Cameroon

The physico-chemical and microbiological characteristics of honey from the sudano-guinean zone of West Cameroon were determined. The indices obtained were within their respective ranges recorded forhoney in temperate countries, except for calcium content whose value was on the upper side of its reference range. A bacterial type and eight fungi species contamination were found to have contaminated the honey from the local markets. However, there were no microbes present in honey harvested from the Bee Research Farm of the University of Dschang. This indicated contamination from secondary sources, during handling and or adulterations of honey from our local markets. Honey used in this study showed medium crystallisation tendency and granulation was faster when stored under dark than light at similar conditions. The mixed floral or nectar sources, fluctuating environmental conditions and processing procedures played major roles in the physico-chemical differences observed between the local and temperate honeys

Totalsynthese und Semisynthetische Derivatisierung von komplexen Cytochalasane und Nitraria-Alkaloide

The general aim of this research was to investigate the total and semi-synthesis of bioactive naturally occurring alkaloids, the translation of their bioactivities into drug development, and the design of tailormade tool compounds for target identification and cell imaging purpose. In the first part of these works, the racemic total synthesis of nitrabirine together with its previously undescribed epimer 2-epi-nitrabirine was accomplished via a six-step route based on a biomimetic late-stage heterocyclization. This allowed the assignment of their relative configuration by the lanthanide-induced shifts (LIS) experiment, which was later on confirmed by X-ray diffraction of nitrabirine single crystals. Furthermore, a Fischer indole reaction gave access to novel tetracyclic nitrabirine-indol hybrid derivatives. Finally, the biological evaluation of nitrabirine, 2-epi-nitrabirine, and all derivatives synthesized in this study revealed general biofilm dispersal effects against Candida albicans. Moreover, specific compounds showed moderate antibacterial activities as well as potent cytotoxic activities. In the second part of these works, a docking study of selected cytochalasans (from natural or commercial sources including cytochalasin B, pyrichalasin H, 4’-azidocytochalasin H, and 19,20-epoxycytochalasin C on monomeric G-actin led to the selection of specific positions in their structure for chemical modifications. First, the effect in vivo and in vitro of cytochalasin B derivatives on the actin polymerization revealed that chemical modification of the 2-position of the 5-membered ring reduces drastically the actin disruption activity. This constitutes a significant step towards understanding the SAR of cytochalasin B derivatives on actin polymerization. Furthermore, fluorescent and photoactivatable derivatives based on BDPFL or Cy-3 dyes and photoremovable protecting groups (PRPGs) respectively were synthesized from pyrichalasin H and 4’-azidocytochalasin H. These derivatives are currently biologically evaluated in actin-associated assays. In addition, the nitroreductase-catalyzed hydrolysis of an artificial glucosinolate (GSL) based on 4’-azidocytochalasin H in the presence of purified chicken G-actin revealed labeling of the latter at two positions of the amino acid sequence. Further studies are currently under investigation to localize the modified amino acids of the sequence. The success of the actin labeling experiment led to the development of a target identification approach with dyes-based artificial GSLs applicable not only for the cytochalasans family but also for other natural products with unknown inhibitable targets. In the third and last part, a preliminary study towards the synthesis of an isoindolone building block for the total synthesis of chaetoglobosin D was investigated. Several attempts to the intermolecular Diels-Alder cycloaddition of a pre-made diene and dienophiles did not lead to the desired isoindolone building block but resulted in the decomposition of the diene and the dienophiles even under acidic conditions between –40°C and –78°C. New alternatives involving intramolecular Diels-Alder precursors to ease the cycloaddition are currently under investigation.Das allgemeine Ziel dieser Forschungsarbeit ist die Untersuchung der Total- und Semisynthese von bioaktiven, natürlich vorkommenden Alkaloiden, die Übertragung ihrer Bioaktivitäten in die Medikamentenentwicklung und das Design maßgeschneiderter Werkzeugverbindungen für die Identifizierung biologischer Wirkstrukturen und Bildgebung in Zellen. Im ersten Teil dieser Arbeiten wurde die racemische Totalsynthese von Nitrabirin zusammen mit seinem zuvor unbeschriebenen Epimer 2-epi-Nitrabirin über einen sechsstufigen Weg basierend auf einer biomimetischen Heterocyclisierung im späten Stadium erreicht. Dies ermöglichte die Zuordnung ihrer relativen Konfiguration durch das Lanthanoid-induzierte Verschiebungs- Experiment (LIS), was später durch Röntgenbeugung von Nitrabirin-Einkristallen bestätigt wurde. Darüber hinaus ermöglichte eine Fischer-Indol-Reaktion den Zugang zu neuartigen tetracyclischen Nitrabirin-Indol-Hybridderivaten. Schließlich zeigte die biologische Bewertung von Nitrabirin, 2-epi-Nitrabirin und allen in dieser Studie synthetisierten Derivaten allgemeine Biofilm-Dispersion gegen Candida albicans. Darüber hinaus zeigten spezifische Verbindungen moderate antibakterielle Aktivitäten sowie starke zytotoxische Aktivitäten. Im zweiten Teil dieser Arbeiten führte eine Docking-Studie ausgewählter Cytochalasane (aus natürlichen oder kommerziellen Quellen, einschließlich Cytochalasin B, Pyrichalasin H, 4'-Azidocytochalasin H und 19,20-Epoxycytochalasin C, an monomerem G-Aktin zur Auswahl bestimmter Positionen in ihrer Struktur für chemische Modifikationen. Erstens zeigte die Wirkung von Cytochalasin-B-Derivaten in vivo und in vitro auf die Aktin-Polymerisation, dass eine chemische Modifikation der 2-Position des 5-gliedrigen Rings die Aktin-Zerstörungsaktivität drastisch verringert. Dies stellt einen bedeutenden Schritt in Richtung der SAR von Cytochalasin-B-Derivaten bei der Aktin-Polymerisation dar. Darüber hinaus wurden fluoreszierende und photoaktivierbare Derivate basierend auf BDPFL- oder Cy-3-Farbstoffen bzw. photospaltbaren Schutzgruppen (PRPGs) aus Pyrichalasin H und 4’-Azidocytochalasin H synthetisiert. Diese Derivate werden derzeit in Aktin-assoziierten Assays biologisch evaluiert. Danach zeigte die Nitroreduktase-katalysierte Hydrolyse eines künstlichen Glucosinolats (GSL) auf der Basis von 4’-Azidocytochalasin H in Gegenwart von gereinigtem Hühner-G-Aktin die Markierung des letzteren an zwei Positionen der Aminosäuresequenz. Weitere Studien werden derzeit untersucht, um die modifizierten Aminosäuren der Sequenz zu lokalisieren. Der Erfolg des Aktin-Markierungsexperiments führte zur Entwicklung eines Zielidentifizierungsansatzes mit farbstoffbasierten künstlichen GSLs, der nicht nur für die Familie der Cytochalasane, sondern auch für andere Naturstoffe mit unbekannten inhibierbaren Zielen anwendbar ist. Im dritten und letzten Teil wurde eine Vorstudie zur Synthese eines Isoindolon-Bausteins für die Totalsynthese von Chaetoglobosin D untersucht. Mehrere Versuche zur intermolekularen Diels-Alder-Cycloaddition eines vorgefertigten Diens und Dienophilen führten nicht zum gewünschten Isoindolon-Baustein, sondern zur Zersetzung des Diens und der Dienophile selbst unter sauren Bedingungen zwischen –40 °C und –78 °C. Neue Alternativen mit intramolekularen Diels-Alder-Vorstufen zur Erleichterung der Cycloaddition werden derzeit untersucht

Partner Selection Strategies in Global Business Ecosystems: Country Images of the Keystone Company and Partner Companies on the Brand Quality Perception

Consumers perceive brand quality from the country of origin of the brand. Global business ecosystems represent multiple countries such as the country of the keystone company and the country of the assembly companies. Thus, the brands of global business ecosystems have multiple countries of origin. This study aims to examine the impacts of the country images of the keystone company and assembly companies on consumers’ brand quality perceptions. In addition, depending on the assembly partner selection strategies of forming a global business ecosystem, the characteristics of the associated countries with the business ecosystem may change. The keystone company may select an assembly partner from a developing country or from a developed country. These two cases are compared to examine the impacts of the combined country images of the keystone and assembly companies. To do so, this study surveys Vietnamese consumers’ perceptions of the brand Hyundai Motor, the country images of South Korea as the country of the keystone company, India as the assembly partner from the developing country, and USA as the assembly partner from the developed country. The collected data were analyzed using a structural equations modeling method and results are discussed with theoretical and managerial implications

Influence of Anthropization on the Diversity of Woody Vegetation in Muskuwaari Transplanted Sorghum Field in the Sudano-Sahelian Zone of Cameroon

Transplanted sorghum is a staple food crop and represents an important part of cereal production in the Far North region. Its cultivation has led to profound agrarian changes and environmental landscape. The main objective of the study carried out from 2017 to 2019 in the Far North area was aimed to study the influence of anthropization on the diversity of woody vegetation, its management and conservation of the transplanted sorghum landscape in the Sudano-Sahelian zone. Population surveys in six (06) villages and floristic surveys through 50 m2 plots in two soil types in these villages were conducted. The results show that the use of herbicide, cutting down and stump removal of woody plants, essential in most cases, have led to profound changes in the Kare with the invasion of the fields by weed plants, post-harvest soil denudation and the disappearance of plant biodiversity. The exploitation of sorghum led to a reduction in the number of woody species from 20 to 9 at the start to the end of the study respectively. Similarly, the average species density decreased over time. The disappearance of 17 individuals was recorded on the clay soil type and 12 on the hydromorphic soil type during the 2 years. Faced with this threat, the practice of agroforestry (4 to 11%), reduction in the use of chemicals (24.19 to 40.32%), abolish harvesting of green wood (0 to 3.33%) and plough to limit the action of fire have been proposed as alternative measures for sustainable exploitation of transplanted sorghum

Phytodiversité et séquestration de carbone des parcs agroforestiers à Borassus aethiopum Mart. (Arecaceae) en zone soudano-sahélienne du Cameroun

Borassus aethiopum, better known as the African dwarf palm, is a recognized tropical species in Africa. It is of great importance for the ecological balance and plays a multifunctional role for the communities surrounding the parks. This study aims to assess the floristic richness and carbon sequestration capacity of these parks in the district of Poli in the North Cameroon region. Ethnobotanical surveys and floristic inventories were carried out in three villages. Five sites, two cultivated and three fallow, were sampled. Allometric and cylinder volume equations were used to estimate the amount of carbon. The populations of the Vallée de rôniers are aware of the benefits they derive from these parks. The regeneration of this essence is done naturally. Fallowed areas are more diverse (31 species) and denser (317 stems per hectare) compared to cultivated areas (25 species, 123 stems per hectare density). The cultivated plots, however, have larger basal areas (11.24 square meter). Five species show high ecological importance indices (Borassus aethiopum, Piliostigma thonningii, Entada africana, Adansonia digitata, Sarcocephalus latifolius, Ficus sycomorus, Annona senegalensis). The park sequesters an average of 86.65 tons of carbon per hectare. The ecological and economic value linked to this quantity of carbon is 317.72 tons of carbon dioxide per hectare and 1766535 FCFA respectively. The value of this species contributes to the subsistence of populations and is an asset for its conservation and rational management. These parks are important reservoirs of biodiversity and play a fundamental role in meeting the needs of the local population. agroforestry parks, Borassus aethiopum, floristic diversity, carbon stock, Cameroo

Phytodiversité et séquestration de carbone des parcs agroforestiers à Borassus aethiopum Mart. (Arecaceae) en zone soudano-sahélienne du Cameroun

Borassus aethiopum plus connu sous le nom de palmier nain africain, est une espèce tropicale répandue en Afrique. Elle est d'une grande importance pour l'équilibre écologique et joue un rôle multifonctionnel pour les communautés environnantes des parcs. Cette étude vise à évaluer la richesse floristique et la capacité de séquestration de carbone de ces parcs de l’arrondissement de Poli dans le Nord du Cameroun. Les enquêtes ethnobotaniques et les inventaires floristiques ont été menés dans trois villages. Cinq sites, dont deux cultivés et trois en jachères, ont été échantillonnés. Les équations allométriques et de volume de cylindre ont été utilisées pour estimer la quantité de carbone. Les populations de la Vallée de rôniers sont conscientes des bénéfices qu’elles tirent de ces parcs. La régénération de cette essence se fait naturellement. Les zones misent en jachère sont plus diversifiée (31 espèces) et plus dense (317 tiges par hectare) comparées à celles cultivées (25 espèces, 123 tiges par hectare de densité). Les parcelles cultivées présentent cependant, des surfaces terrières plus importantes (11,24 mètres carrés). Cinq espèces présentent des indices d’importance écologique élevés (Borassus aethiopum, Piliostigma thonningii, Entada africana, Adansonia digitata, Sarcocephalus latifolius, Ficus sycomorus, Annona senegalensis). Le parc séquestre en moyenne 86,65 tonnes de carbone par hectare. La valeur écologique et économique liée à cette quantité du carbone est de 317,72 tonnes de dioxyde de carbone (CO2) par hectares et 1766535 FCFA respectivement. La valeur de cette espèce contribue à la subsistance des populations et constitue un atout en faveur de sa conservation et de sa gestion rationnelle. Ces parcs constituent d’importants réservoirs de biodiversité et jouent un rôle fondamental dans la satisfaction des besoins de la population locale.Borassus aethiopum, better known as the African dwarf palm, is a recognized tropical species in Africa. It is of great importance for the ecological balance and plays a multifunctional role for the communities surrounding the parks. This study aims to assess the floristic richness and carbon sequestration capacity of these parks in the district of Poli in the North Cameroon region. Ethnobotanical surveys and floristic inventories were carried out in three villages. Five sites, two cultivated and three fallow, were sampled. Allometric and cylinder volume equations were used to estimate the amount of carbon. The populations of the Vallée de rôniers are aware of the benefits they derive from these parks. The regeneration of this essence is done naturally. Fallowed areas are more diverse (31 species) and denser (317 stems per hectare) compared to cultivated areas (25 species, 123 stems per hectare density). The cultivated plots, however, have larger basal areas (11.24 square meter). Five species show high ecological importance indices (Borassus aethiopum, Piliostigma thonningii, Entada africana, Adansonia digitata, Sarcocephalus latifolius, Ficus sycomorus, Annona senegalensis). The park sequesters an average of 86.65 tons of carbon per hectare. The ecological and economic value linked to this quantity of carbon is 317.72 tons of carbon dioxide per hectare and 1766535 FCFA respectively. The value of this species contributes to the subsistence of populations and is an asset for its conservation and rational management. These parks are important reservoirs of biodiversity and play a fundamental role in meeting the needs of the local population. agroforestry parks, Borassus aethiopum, floristic diversity, carbon stock, Cameroo

Exploitation des fleurs de Ageratum conyzoides, Sida rhombifolia et Stylosanthes guianensis par Apis mellifera (Hymenoptera: Apidae) à Dang (Ngaoundéré, Cameroun)

A Dang (Ngaoundéré, Cameroun), d’avril à décembre 2015 et 2016, les fleurs de Ageratum conyzoides L., Sida rhombifolia L. et Stylosanthes guianensis (Aublet) Swartz ont été observées en vue de l’étude de l’activité de butinage de Apis mellifera L. Les fleurs de chacune de ces espèces végétales ont été prospectées deux jours par semaine, les mercredis et vendredis, entre 7h 00 et 18h 00, période subdivisée en trois tranches horaires (7h 00-11h 00, 11h 00-15h 00 et 15h 00- 18h 00). Les résultats montrent que les butineuses de A. mellifera fréquentaient intensément et régulièrement chacune de ces espèces végétales pour la récolte du pollen. Cette abeille prélevait fortement le nectar chez S. rhombifolia et S. guianensis. Chez A. conyzoides cette activité était faible. Le plus grand nombre de butineuses de A. mellifera simultanément en activité sur 1000 fleurs variait de 54 (A. conyzoides) à 125 (S. rhombifolia). Ageratum conyzoides, S. rhombifolia et S. guianensis sont des plantes apicoles fortement pollinifères pouvant être cultivées et protégées pour augmenter la production du pollen comme produit de la ruche. Sida rhombifolia et S. guianensis sont des plantes apicoles fortement nectarifères pouvant être cultivées et protégées pour accroitre la production du miel. Sur chacune de ces plantes, les ouvrières de A. mellifera transportaient le pollen de fleur en fleur et peuvent ainsi être considérées comme des pollinisateurs.Mots clés: Ageratum conyzoides, Sida rhombifolia, Stylosanthes guianensis, Apis mellifera, plante apicole, pollinisationEnglish AbstractAt Dang, from April to December 2015 and 2016, Apis mellifera L. workers foraging activity was studied on the flowers of three plants species, Ageratum conyzoides L., Sida rhombifolia L. and Stylosanthes guianensis (Aublet) Swartz. At Dang, the flowers of each plants species were observed two days per week, the Wednesdays and Fridays between 07h.00 and 18h.00, for recording the pollen and/or nectar foraging behaviour of A. mellifera workers. Results show that, A. mellifera harvested intensely and regularly the pollen of each plant species. In addition, S. rhombifolia and S. guianensis were also visited intensely and regularly for nectar; A. conyzoides was also visited for nectar but slightly. The greatest mean number of workers foraging simultaneously on the flower was 1 for each plant species, per 1000 varied from 54 (A. conyzoides) to 125 (S. rhombifolia). Apis mellifera workers visited the flowers of plants species others during foraging bouts. Consequently, A. conyzoides, S. rhombifolia and S. guianensis are highly polliniferous bee plants that can cultivated and protected to increase pollen production as a hive product. Sida rhombifolia and S. guianensis are highly nectariferous bee plants that can be cultivated and protected to increase the honey production. During foraging, A. mellifera workers carried pollen from flower to flower and improved pollination possibilities of each plant species and can thus be considered as pollinator.Keywords: Ageratum conyzoides, Sida rhombifolia, Stylosanthes guianensis, Apis mellifera, bee plant, pollinatio