Agatharesinol biosynthesis-related changes of ray parenchyma in sapwood sticks of Cryptomeria japonica during cell death.

MAIN CONCLUSION: The work demonstrates a relationship between the biosynthesis of the secondary metabolite, agatharesinol, and cytological changes that occur in ray parenchyma during cell death in sapwood sticks of Cryptomeria japonica under humidity-regulated conditions. To characterize the death of ray parenchyma cells that accompanies the biosynthesis of secondary metabolites, we examined cell death in sapwood sticks of Cryptomeria japonica under humidity-regulated conditions. We monitored features of ray parenchyma cells, such as viability, the morphology of nuclei and vacuoles, and the amount of starch grains. In addition, we analyzed levels of agatharesinol, a heartwood norlignan, by gas chromatography-mass spectrometry in the same sapwood sticks. Dramatic changes in the amount of starch grains and in the level of agatharesinol occurred simultaneously. Therefore, the biosynthesis of agatharesinol appeared to originate from the breakdown of starch. Furthermore, we observed the expansion of vacuoles in ray parenchyma cells prior to other cytological changes at the final stage of cell death. In our experimental system, we were able to follow the process of cell death and to demonstrate relationships between cytological changes and the biosynthesis of a secondary metabolite during the death of ray parenchyma cells.

Seasonal variation of heartwood formation in Larix kaempferi.

Heartwood in tree stems provides natural durability and ornamental values to wood products as well as antimicrobial properties to protect living stems from decay. Control of the amount and quality of heartwood is required because of its importance in wood utilization. Despite the importance, the mechanism of heartwood formation has been poorly understood. To obtain further knowledge for understanding this mechanism, we studied the seasonal variation of various components of heartwood formation in Larix kaempferi (Lamb.) Carrière. Dehydration of tracheids at the boundary between sapwood and intermediate wood occurred continuously during the study period. The death of ray parenchyma cells at intermediate wood occurred from spring to summer. The deposition of heartwood substance took place in autumn to winter. Thus, different components of heartwood formation were active in different seasons. Since heartwood formation is a system consisting of several components within a series of continuing processes, understanding the seasonal change of heartwood formation requires monitoring these components simultaneously.