We studied the between-tree and within-tree variation in the composition and content of foliar low-molecular-weight phenolics (LMWP) of European white birch (Betula pendula Roth) during the unfolding of vegetative buds and during early leaf development. In buds, the major groups of phenolic compounds were hydrolysable tannins and flavonoid aglycones, whereas, later during leaf development, the flavonoid glycosides accounted for most of the total LMWP. The content of total LMWP, as well as individual compounds, varied largely among individual trees, while variation within an individual tree was low. The biosynthetic origin of individual compounds or compound groups is discussed in order to explain the main patterns in leaf chemistry during bud unfolding and early leaf development.

Plant secondary chemistry is determined by both genetic and environmental factors, and large intraspecific variation in secondary chemistry has frequently been reported. The heritability of specific tree secondary metabolites is, however, mostly unknown. We tested the effect of plant genotype, environment, and ontogeny on the variation in shoot secondary chemistry of juvenile and mature European white birches (Betula pendula). Phenolic compounds and triterpenoids were analyzed in 30 naturally regenerated 20-year-old parental trees and micropropagated plantlets that originated from 14 of those same parental trees, planted at four growing sites. Most of the variation for phenolic compounds was explained by differences between parental trees, whereas triterpenoids had a high variation both between parental trees and within the canopy of individual tree. The effect of ontogeny was strong for some individual compounds. In mature trees, the amount of triterpenoids was less than 1 mg/g (DW), whereas the concentration in juvenile plantlets was up to 64 mg/g (DW). Clonal plantlets and parental trees were generally quite similar in their phenolic contents, but there were significant differences for all analyzed compounds among clones. Environment had no significant effect on the accumulation of some compounds, whereas for others, a significant environmental effect and/or significant genotype by environment interaction was found. These results suggest that birch shoot secondary chemistry is under strong genetic control and that the environmental effects depend on the studied chemical trait.

Variation in birch bark secondary chemistry between and within clones: implications for herbivory by hares. -Oikos 104: 316-326.We studied the variation in bark chemistry between and within 19 European white birch (Betula pendula) clones and its implications to resistance to the mountain hare (Lepus timidus). We used one-year-old clonal plantlets originating from randomly selected naturally regenerated parental trees. The same clones were used in both chemical analyses and in feeding experiments. The condensed tannins were analysed by an acid butanol assay, other phenolic components by HPLC-DAD, and triterpenoid components by HPLC-MS. The resistance to hare was tested in open-field feeding experiment. The main phenolic compounds in birch bark were catechin derivatives, rhododendrin, platyphylloside, and condensed tannins, and the main triterpenoids were papyriferic acid and pendulic acid. Most of the variation in the concentrations of the studied compounds was found between clones for the studied phenolics and large variation for triterpenoid components were found both between clones and among plantlets within the same clone. Hares clearly selected among the studied clones. Our results suggest that birch bark chemistry play an important role in resistance to herbivory by hare. The total triterpenoids and total flavonoidaglycones showed significant negative correlation with hare feeding. It seems that a genetic basis for bark chemistry and birch resistance is strong. Such a high variation in secondary chemistry both between clones and within individual clones indicates that European white birch populations have a good resistance towards variable environmental conditions and varying pressures from herbivory.M.-L. Laitinen, K. Yamaji and M. Rousi, Finnish Forest Res. Inst., Punkaharju Res. Stn,

Hydroxyimine derivatives of ketoprofen (1) and nabumetone (2) were synthesized and evaluated in vitro and in vivo as cytochrome P450-selective intermediate prodrug structures of ketones. 2 released nabumetone in vitro in the presence of isolated rat and human liver microsomes and in different recombinant human CYP isoforms. Bioconversion of 2 to both nabumetone and its active metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA), was further confirmed in rats in vivo. Results indicate that hydroxyimine is a useful intermediate prodrug structure for ketone drugs.

No abstract