The bark of Taxus brevifolia Nutt., a forest tree species of the Pacific Northwest, is an important source of taxol, a potent anticancer compound showing promise against a variety of tumors. Without intervention, wild trees will not be able to supply the quantities of taxol needed; moreover, species survival is potentially threatened by large-scale bark stripping. Selective breeding and cultural techniques would increase yields and reduce the pressure on wild trees. The broad goal of this research is to furnish critical information directly applicable to increasing taxane production as rapidly as possible by vegetative propagation, horticultural techniques, and genetic selection of superior genotypes.
A specific aim i s to determine the genetic and physiological potential of the species to produce important taxanes. In a study designed to test genetic variation, cuttings of 50 field-selected trees will be rooted in a greenhouse to minimize environmental interactions. Oven-dried and ground tissues will be methanol extracted and partitioned with methylene chloride and water. Taxol and five other taxanes usable in hemisynthesis of taxol will be analyzed by high performance liquid chromatography. UV and mass spectra of standards will be used to verify identity of compounds. Preliminary studies indicate shading influences taxane concentrations. Cuttings selected from the original 50 genotypes will be used in a factorial study designed to determine light and nutrient levels needed for optimizing growth and taxane production in foliage and stems. The effect on taxane production of rapid growth associated with rejuvenation will be evaluated also. In field-sampled trees, diurnal and seasonal variation of six important taxanes will be measured in needles and bark. Mobility of glycosidic taxanes may contribute to the variation. Mobility may be inferred by constricting the conductive tissue and measuring taxane concentrations above and below the constriction. Another specific aim will be to analyze and test vegetative propagation including grafting scions of high taxane-- producing genotypes onto more rapidly growing rootstocks to increase their harvestable biomass. Hedging and field-pruning procedures designed to stimulate foliage and stem growth will be assessed by measuring 2-year growth and taxane concentrations per unit weight and surface area. Cultural techniques developed from this research would significantly contribute to a management system that could increase the supply of taxol without sacrificing wild trees.
| Vance, N C; Kelsey, R G; Sabin, T E (1994) Seasonal and tissue variation in taxane concentrations of Taxus brevifolia. Phytochemistry 36:1241-4 |
