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.

A linear displacement transducer was used to measure the leaf thickness of sun and shade leaves collected from trees growing in the mountain and eastern coalfield region of Kentucky. Leaf thickness measurements are presented for 64 southern Appalachian forest species which occupy all strata of the forest communities. Leaf thickness varied from 117.1 μm in Hydrangea arborescans to 473.9 μm in Ilex opaca. In all species sun leaves were thicker than shade leaves. Species considered tolerant of shade had significantly thicker sun and shade leaves than intolerant species when shrubs were included. When shrubs were excluded the sun and shade leaves of tolerant species were thinner than sun and and shade leaves of intolerant species. For all species including shrubs, sun leaf thickness for the tolerant, medium, and intolerant classes averaged 220.1, 183.5, and 213.3 μm, respectively. Although there appeared to be differences in leaf thickness between species inhabiting xeric and mesic sites, these differences were not statistically significant. Variation in sun leaf thickness within the genus Quercus ranged from 130.6 μm in Quercus alba to 306.5 μm in Quercus stellata. Shrub species generally had the thickest leaf blades.

One-year-old Camptotheca acuminata seedlings were grown under heavy shade (27% full sunlight), slight shade (67% full sunlight), or full sunlight for 2 weeks, then subjected to flooding for 4 weeks under continued shading schemes. Growth, chlorophyll fluorescence, and camptothecin concentrations were determined. Flooding led to significant decreases in leaf biomass, while shading significantly increased stem biomass. Under full sunlight or slight shade conditions, lateral root biomass was significantly decreased by flooding, whereas under heavy shade, it was not significantly reduced by flooding. Shaded leaves displayed significantly higher chlorophyll fluorescence than the non-shaded leaves throughout the 6-week period. Onset of flooding caused immediate decline of chlorophyll fluorescence of nonshaded and slight-shaded seedlings, but the effect of flooding quickly diminished. Heavy shade led to elevated camptothecin concentrations in leaves, whereas flooding had no effect. Camptothecin concentrations in stems were not altered by either flooding or shading; however, they were substantially lowered in lateral roots under heavy shade compared with those grown in full sunlight. Flooding induced an additional camptothecin accumulation in lateral roots under slight shade, but it failed to do so under either heavy shade or full sunlight conditions. Key words: anti-tumor compounds, camptothecin, chlorophyll fluorescence, flooding, secondary metabolites, shading.

No abstract

In 1972 and 1973 a scanning electron microscope was used to study stomata and cuticular surfaces of shade leaves collected from trees growing in the mountain and eastern coalfield region of Kentucky. Stomatal frequency and size determinations are presented for about 50 southern Appalachian forest species. Stomata varied from 6534/cm2 in Asimina triloba to 90 909/cm2 in Quercus palustris. Mesic species had fewer stomata per unit leaf surface area than xeric species. Stomatal frequency was not related to shade tolerance. The largest stomata (35 microns (μ)) were found in Populus gileadensis while the smallest (5μ) occurred in Quercus coccinea.