Boron mobility in deciduous forest trees in relation to their polyols

Boron (B) has been found to be phloem mobile in species that translocate polyols, whereas it is almost immobile in other species. The objectives of the present study were to survey B mobility in deciduous trees, and to relate it to the presence of polyols. The stable isotope B-10 was applied as a tracer to mature leaves of seedlings, and growing leaves were subsequently harvested for B isotope analysis. Extensive B mobility was found in Sorbus aucuparia and Prunus padus, species with high sorbitol content, but also in Ulmus glabra, with only trace amounts of B-complexing polyols. Alnus incana, Fraxinus excelsior, Betula pubescens and Larix sibirica also translocated B-10 into new leaves. Mannitol in Fraxinus and pinitol in Larix probably explain this. A. glutinosa did not remobilize B, although the polyol concentrations were almost identical to A. incana, a closely related species. B mobility was not as closely related to the presence of polyols as expected, and it appears that to some degree remobilization occurs in many plant species. (C) New Phytologist (2004).