Radial changes and spatial distribution patterns of xylem parenchyma cell metabolites during heartwood formation in Dalbergia odorifera

Heartwood in tree stems gives wood products durability and aesthetic properties. Scientific and effective regulation of the quantity and quality of heartwood formation is an effective means to increase the economic value of forest trees, however, the process of heartwood formation has not been clearly understood so far. In order to understand the role of secondary metabolites in heartwood formation, metabolite changes and distribution in the xylem of Dalbergia odorifera were explored. A dataset of 954 metabolites in the xylem of D. odorifera was constructed. Among them, sapwood characteristic metabolites such as sucrose and glutamate can provide energy and material basis for the vital activity of parenchyma cells. Differential metabolites associated with heartwood formation are primarily enriched in flavonoids and terpenoids biosynthesis pathways. The distribution of characteristic secondary metabolites in various tissue of the xylem was not uniform, and flavonoid compounds appeared firstly in parenchyma cells, which had higher contents than fiber. The heartwood substances were mainly deposited in the pits, corner and the intercellular space of the cell wall. The changes and distribution patterns of metabolites can provide a fundamental basis for finding key regulatory genes and understanding the process of heartwood formation. • A dataset of 954 metabolites from D. odorifera xylem was established. • HW formation-associated differential metabolites primarily enriched in flavonoids and terpenoids biosynthesis. • Mass spectrometry imaging was applied to determine the spatial distribution of characteristic metabolites in the xylem.