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.

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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.

Whenever supplemental irrigation was applied to sweet potatoes, root quality was reduced. Dry matter content, color of both fresh and processed sweet potatoes, firmness of the canned product, and percent protein decreased as the moisture content of the soil increased. Moisture content had little or no influence on fiber content or cortex thickness of fleshy roots. Nitrogen levels also influenced quality factors. As N levels increased there was a reduction in flesh color and increases in protein content and firmness of the canned potatoes. Nitrogen had little effect on fiber content, dry matter content or cortex thickness. Yearly variations occurred for dry matter content, fiber content, firmness of the canned product and flesh color.

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