Savinin Triggers Programmed Cell Death of Ray Parenchyma Cells in Heartwood Formation of Taiwania cryptomerioides Hayata

The purpose of this study was to investigate the relationship between lignan biosynthesis and programmed cell death (PCD) of ray parenchyma cells during the heartwood formation of Taiwania (Taiwania cryptomerioides Hayata). Since the PCD of ray parenchyma cells and the synthesis of lignans are the two main processes involved in the formation of heartwood, both of which need to be completed through gene regulation. Based on the results of genomics and bioinformatics analysis, that the PCD of tracheids are induced by genotoxic, and the PCD of ray parenchyma cells is induced by biological factors, such as fungi, bacteria, and viruses, which could induce oxidative stress. According to the results of time−of−flight secondary ion mass spectrometry (ToF−SIMS) analysis, lignans are produced in ray parenchyma cells, and the accumulation of savinin and its downstream lignans might be the cause of PCD in ray parenchyma cells. An in vitro experiment further confirmed that the accumulation of savinin could cause protoplasts of Taiwania’s xylem to produce taiwanin A, which is the marker of heartwood formation in Taiwania. Resulting in an increase in reactive oxygen species (ROS) content, which could induce oxidative stress in ray parenchyma cells and potentially lead to PCD. Based on these findings, we conclude that accumulation of savinin could be induced PCD of ray parenchyma cells in heartwood formation in Taiwania.