Variations in the secondary metabolite camptothecin in relation to tissue age and season in Camptotheca acuminata

Abstract

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.

Effect of NaCl on growth, morphology, and camptothecin accumulation in Camptotheca acuminata seedlings

“…Following these measurements, two circular discs (5 mm in diameter) were punched (in the middle of the blade and beside the main vein in order to reduce the damage to seedlings and to minimize the possible CPT variation due to leaf size and disc location on leaves) from each of the fifth and sixth leaves on each seedling. A previous study found that leaves at positions 5 and 6 from the apex, which are fully expanded leaves, have relatively more stable CPT concentrations than leaves at positions 1, 2, 3, and 4 (Liu et al 1998). The collected leaf discs were immediately put into a 1.5-mL pre-weighed Eppendorf tube, frozen in liquid N 2 , subsequently freeze-dried, and stored in a refrigerator (2-8°C) for CPT analysis.…”

“…CPT concentrations varied significantly with leaf age and tree age, where high CPT concentrations were found in young leaves and young trees (Liu et al 1998). Shading of whole seedlings caused increased CPT concentration in leaves and decreased CPT concentration in roots (Liu et al 1997).…”

“…As a secondary metabolite, it is hypothesized to defend the plant against stresses (Liu et al 1997(Liu et al , 1998. CPT accumulates in leaves, stems, and roots of C. acuminata and leaves have relatively higher CPT concentrations than stems and roots (Liu et al 1997(Liu et al , 1998. Therefore, leaves are mainly used in repeated and nondestructive harvesting for CPT (Lopez-Meyer et al 1994).…”

<b>The influence of planting and harvesting times on the total phenolic content and antioxidant activity of <i>Talinum triangulare</i> (Jacq.) Willd

“…This defense strategy evolves to produce secondary metabolites to protect the leaves during their normal ontogeny. The tender young leaves are vulnerable to pests and diseases (SCOGINGS et al, 2004;LIU et al, 1998).…”

“…These effects depend on the growth stage and on the plant part assessed. Stress can also influence the release of polyphenols from vacuoles as well as the new synthesis of phenols (McCONCHIE et al, 1994). For example, groups of phenolics such as ferulic acid and p-coumaric acid are commonly found in the roots, while isoflavonoids occur primarily in the leaves and are less prevalent in the petioles, stems and roots (SIQUEIRA et al, 1991).…”