TAXOL AND CEPHALOMANNINE CONCENTRATIONS IN THE FOLIAGE AND BARK OF SHADE-GROWN AND SUN-EXPOSED TAXUS-BREVIFOLIA TREES

Taxol and cephalomannine concentrations were measured in the bark and foliage of Pacific yew trees growing in the shade of a forest canopy and at a site nearby where trees had been exposed to full sunlight for 6 years. Bark was the only tissue showing concentration differences due to light, with significantly greater quantities of both compounds in the bark of shaded trees than in the bark of sun-exposed trees. In either light regimen taxol concentrations were greater in the bark than in the needles or twigs. Taxol concentrations were higher in older needles than in younger needles, and the reverse was observed for twigs. Cephalomannine was substantially lower than taxol in concentration. Cephalomannine varied similarly to taxol among tissues of shade trees but not among tissues of sun-exposed trees.