Bayreuther Institut für Terrestrische Ökosystemforschung
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BFÖ 17: Höft, MG: Aut-ecological studies on
STAPF. (Apocynaceae) in the Shimba Hills (Kenya) with special reference to their alkaloid contents (6 Euro)
Höft, MG (1995)
Since ancient times several species of the plant family of Apocynaceae are known for their powerful pharmaco-logical actions. In the African tree species Tabernaemontana pachysiphon Stapf and Rauvolfia mom-basiana Stapf these actions are due to the presence of different indole alkaloids in all plant organs. Both plants are widely used in traditional African medicine. The levels of indole alkaloids are known to fluctuate in response to various environmental and plant inherent factors. The particular challenge therefore is to elucidate the extent to which the interactions between abiotic factors on the one hand and plant internal or biotic factors on the other hand alter alkaloid contents. In this study the dominant factors of influence are singled out. Tabernaemontana pachysiphon and Rauvolfia mombasiana are common in remnants of the tropical evergreen seasonal lowland forest in the Shimba Hills in Southern Kenya. Their distribution ranges from nearly undisturbed natural forest vegetation and forest plantations to highly disturbed open bushland, and encompasses different soil types. The environmental gradients run along the distinct vegetation types from moist and shady sites with high nitrogen supply to dry and sun-exposed sites with lower nitrogen supply. However, growth and performance of both species in the natural habitat is mainly governed by recurring animal disturbances. The influence of the different abiotic factors found in the natural habitat on alkaloid contents is corroborated by greenhouse experiments. Furthermore, the relationship between plant growth and alkaloid accu-mulation is demonstrated under the same conditions in the greenhouse. Within a limited geographic range, the relative amounts of alkaloids can thus be assessed from the plants" estimated age and performance, as well as the environmental conditions at a particular growing site.
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