Abstract: Many tropical tree species generate natural decay resistance by producing bioactive metabolites. Among them, Sextonia rubra (Lauraceae) is a widely exploited species for construction in French Guiana. Rubrynolide and rubrenolide, which are secondary metabolites isolated from the stem wood of S. rubra, exhibit potent antifungal and termiticidal activities that result in the exceptional durability of the heartwood. Although the structure and total synthesis of these two biologically active compounds have been well described in literature, little is known about their cellular localization or biosynthesis process in living trees. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been well known for its high lateral resolution imaging with a typical beam size of 0.4-2 µm, thus sufficient to image the wood surface at subcellular level.
Wood surfaces of sapwood, transition zone and heartwood from living trees of S. rubra were prepared with ultramicrotome using diamond knife. Each surface was mapped by Bi3+ cluster TOF-SIMS with high lateral resolution (~ 0.4 µm) which was achieved by employing burst alignment primary ion focusing mode with an extraction delay of the secondary ions to improve mass resolution. 3D imaging of a multi-structure wood sample was performed using dual beam depth profiling method, with 25 keV Bi3+ and 10 keV Ar1000+ as analysis and sputter beam, respectively. To examine the effect of life-history traits on the production of bioactive metabolites, the corresponding counterparts from a tree which had suffered stress during growth were investigated as well.