Unraveling the role of dragon’s blood in the undisturbed growth of dragon trees

Abstract

Key message: Dragon’s blood secretion is an integral part of the normal development of the leaves and of the tissue protecting the trunk of dragon trees. Abstract: Dragon’s blood is a common name of a red resin produced in response to wounding by tree-like monocot species of the genus Dracaena (Asparagaceae), known as dragon trees. This resin has important medicinal uses and economic value. However, its ecological significance and mechanism of secretion are understudied. We specifically addressed this knowledge gap through the investigation of leaf shedding, a natural processes in plant development, associated with self-wounding. We aimed to characterize the form of the resin of the Macaronesian (D. draco, D. tamaranae) and Socotran (D. cinnabari) dragon trees, and to explain its role in the development of leaves and of the tissue covering the leafless mature trunks. Based on the NADI test and the analysis of large-area longitudinal sections, we show for the first time that the resin occurs in parenchyma cells in the form of terpene-filled vesicles which tend to aggregate. The resin is an anatomical marker of the area where the leaf’s abscission zone will be formed. After leaf shedding, the resin containing leaf scars completely cover the trunk. This study highlights that dragon’s blood is secreted not only following wounding caused by external biotic and/or abiotic factors, but also in the undisturbed growth of dragon trees.