VARIATIONS IN THE SECONDARY METABOLITE CAMPTOTHECIN IN RELATION TO TISSUE AGE AND SEASON IN CAMPTOTHECA-ACUMINATA

We investigated variation in concentration of the secondary metabolite , camptothecin (CPT), in relation to leaf, branch and tree age, season , and leaf drying method in Camptotheca acuminata Decaisne saplings. Y ounger leaves contained higher CPT concentrations than older leaves. W ithin a branch, there was a linear decline in CPT concentration from l eaves at the apex of the branch down to Leaf 7. Comparing leaves of si milar age, those from younger trees had higher CPT concentrations than those from older trees. Over the course of the growing season, there was a steady decline of 11% per month in leaf CPT concentration. Branc hes showed a similar seasonal decline in CPT concentration to leaves; however, the rate of decline was threefold greater in leaves than in b ranches. Freeze-dried tissues had a 27% higher CPT concentration than oven-or air-dried tissues, suggesting that oven-and air-drying caused degradation of CPT. The decline in CPT concentration with tissue aging may reflect a genetically determined mechanism whereby, in young tree s, chemicals serve as a first line of defense against attacks by herbi vores and pathogenic microorganisms until other mechanisms are develop ed and deployed. We hypothesize that chemical defense mechanisms are p rogramed for early ontogenic stages, whereas they are induced by bioti c and abiotic factors during later ontogenic stages.