Correlations between selected monoterpene hydrocarbons in the xylem of sixPinus (pinaceae) species

The compositions of 23 monoterpene hydrocarbons of six pine species (Pinus sylvestris, P. yunnanensis ll,ris, P. armandii, P. tropicalis, P. cubensis and P. caribaca) were compared, using multivariate data analysis. Four of t he six species were clearly different from the other species in a Principal Components Analysis (PCA) model, based on the relative amounts (selective normalization) of the monoterpenes. The correlation coefficients between co nstituents were determined separately for each species and the strongest co rrelations were found between (+)-alpha -pinene and (+)-camphene and betwee n the corresponding (-)-enantiomers, in all species. This pattern, i.e. a g ood correlation in all species, was neither shown by the correlation of the structurally more similar (+)-alpha/beta -pinenes, nor by the (-)-alpha/be ta -pinenes or within the enantiomeric pairs of alpha -pinene and beta -pin ene. For these pairs of monoterpenes, good correlations were found in some species. None of the species showed good correlations in all the investigat ed monoterpene pairs presented here. Correlations between monoterpenes in i nsect-attacked trees (P. cubensis and P. caribaea, attacked by Dioryctria h orneana, and P. yunnanensis, attacked by Tomicus piniperda) were also deter mined. The results are discussed from chemotaxonomic and biosynthetic point s of view.