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Study of wood metabolites by submicron resolution Cluster-TOF-SIMS imaging.

Vanbellingen Q., Fu T., Elie N., Eller M., Amusant N., Touboul D., Stien D., Della Negra S., Brunelle A.. 2015. seatle : s.n., 1 p.. International Conference on secondary ion mass spectrometry (SIMS). 20, 2015-09-15/2015-09-18, Seattle (Etats-Unis).

Heartwood formation study is of great interest in the di scovery of new natural compounds. It usually follows the death of parenchyma cells and tyloses formation. Cell apoptosis seems to be correlated with the biosynthesis of secondary metabolites, allowing trees to defend themselves ag ainst pests [1]. Although the analysis of secondary metabolites in ligneous species is now well established, their localization by surface analysis has not been fully explored [2]. Our purpose is to map the chemical co mposition in-between sapwood and heartwood to understand heartwood formation process. A TOF-SIMS IV mass spectrometer (ION-TOF GmbH, Münste r, Germany) equipped with a bismuth cluster ion source (Bi 3 + , 25 keV) was used. Samples of sapw ood, heartwood and transition zone from Dicorynia guianensis ,a tree species from French Guiana, which is well-known for its decay-resistant heartwood, were imaged after being cut with a diamond knife. A first set of images has been recorded over large areas with 8 µm pixel size. Then, submicron resolution ion images have been acquired. To overcome the topographic effect and to obtain simultaneously high spatial and mass resolution, delayed extraction of secondary ions was characterized, and used [3]. Lignin and polysaccharides fragment ions have been mapped using the mass assignments from Goacher et al. [4]. A strong spatial correlation between lignin and polysacchar ides ions has been establis hed. Tryptamine fragment ions were also detected, with higher intensities detected in heartwood than in sapwood. This demonstrated that the biosynthesis of tryptamine mostly occurs in the hear twood formation process. High spatial resolution (0.4 µm) images acquired by tuning the mass spectrometer with a de layed extraction revealed that in the heartwood region tryptamine fragments are localized in parenchyma cells from transition zone and then diffuse to all heartwood cell walls. Heterogeneous distribution of tryptamine indicates this compound can be involved in the durability of heartwood. Decrease in inorganic and starch fragment ion intensities indicate that heartwood is less nutrient for pest insects. These comparisons between different wood tissues bring new and extensive information to understanding heartwood formation. This work has benefited from an ¿Investissement d'Avenir¿ grant managed by the Agence Nationale de la Recherche (CEBA, ref ANR-10-LABX-0025).

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