© 1998 Heron Publishing—Victoria, Canada
Variations in the secondary metabolite camptothecin in relation to tissue age and season in Camptotheca acuminata
Zhijun Liu (1), Stanley B. Carpenter (1), Wayne J. Bourgeois (2), Ying Yu (1), Roysell J. Constantin (2), Matthew J. Falcon (2) and John C. Adams (3)
1. School of Forestry, Wildlife and Fisheries, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural
Center, Baton Rouge, LA 70803, USA / 2. Citrus Research Station, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Rt. 1,
Box 628, Port Sulphur, LA 70083, USA / 3. School of Forestry, Louisiana Tech University, Box 10138 T.S., Ruston, LA 71270, USA /
Summary
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. Younger leaves contained higher CPT concentrations than older leaves. Within a branch, there was a linear
decline in CPT concentration from leaves at the apex of the branch down to Leaf 7. Comparing leaves of similar 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. Branches showed a similar seasonal decline in CPT concentration
to leaves; however, the rate of decline was threefold greater in leaves than in branches. 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 trees, chemicals serve
as a first line of defense against attacks by herbivores and pathogenic microorganisms until other mechanisms are developed
and deployed. We hypothesize that chemical defense mechanisms are programmed for early ontogenic stages, whereas they are
induced by biotic and abiotic factors during later ontogenic stages.
Keywords:
alkaloids, chlorophyll, drying methods, ontogeny, seasonal variation.
