Seasonal and tissue variation in taxane concentrations of Taxus brevifolia

Analysis of seven taxanes: taxol, baccatin III, 10-deacetyltaxol, 10-deacetylbaccatin III, 7-xylosyl-10-deacetyltaxol, cephalomannine and brevifoliol in extracts from bark and foliage of pacific yew (Taxus brevifolia) showed a gradient of decreasing concentration from stem base to branch tip. This decrease is attributed to the generally higher concentration of taxanes in the phloem tissue and the decrease in inner bark thickness from base to branch tip. Analysis of taxanes extracted from stem bark and needles sampled over a growing season showed that most taxane concentrations were significantly lower in the needles than in the bark. Typically, taxane concentrations in bark increased from May through August; whereas, in needles, concentrations changed little during that period. Two exceptions were baccatin III, which in the summer reached levels equivalent to bark, and brevifoliol which increased from March to August, reaching levels in needles nine times greater than bark.