Ryogo Nakada

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.

Clonal variation of carbon content in wood of Larix kaempferi (Japanese larch)

Variations in carbon content in wood among 102 clones, selected from almost the entire natural distribution area, were investigated in Larix kaempferi. The average carbon content was 50.50%, 50.94%, and 50.80% in sapwood, heartwood, and whole wood, respectively. The difference in carbon content between clones was significant. The clonal repeatabilities were 0.46, 0.38, and 0.44 in heartwood, sapwood and whole wood, respectively. The coefficients of variation in the clonal mean carbon content were only 0.43%, 0.42%, and 0.41% in heartwood, sapwood, and whole wood, respectively. This small genetic variation and resulting small relative genetic gain of carbon content indicate that the genetic improvement of carbon content by selection has a small effect on the genetic improvement of carbon sequestration capacity by selection in L. kaempferi.

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

AbstractMain conclusionThe 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 ofCryptomeria japonicaunder 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.

Clonal variation in heartwood norlignans of Cryptomeria japonica: evidence for independent control of agatharesinol and sequirin C biosynthesis

Abstract• IntroductionIn Cryptomeria japonica, heartwood properties are considered to be affected by specific extractives. It remains unclear whether traits of specific heartwood compounds are under genetic control.• MethodsTwo major heartwood norlignans, agatharesinol (A) and sequirin C (S), were determined quantitatively and qualitatively in 29 C. japonica plus-tree clones to evaluate their clonal variations and clonal repeatability.• ResultsThe content of two norlignans and their composition (S)mol/((A)mol + (S)mol) varied significantly depending on the clone, suggesting that the biosynthesis of norlignan is genetically regulated in C. japonica. In particular, the clonal repeatability of sequirin C was higher than that of both agatharesinol and total norlignan content. In addition, the clonal repeatability of the norlignan molar ratio was quite high. These results suggested that genetic involvement is greater in the accumulation of sequirin C than agatharesinol. No significant correlation was found between agatharesinol and sequirin C content, or between the total norlignan content and the norlignan molar ratio, suggesting that the formation of agatharesinol and sequirin C in norlignan biosynthesis is independently controlled in C. japonica.• ConclusionsIt was suggested that the traits of the specific heartwood extractive norlignans were under genetic control in C. japonica.

Responses of ray parenchyma cells to wounding differ between earlywood and latewood in the sapwood of Cryptomeria japonica

Key messageChanges in cellular contents of ray parenchyma cells during the formation of reaction zone differ between earlywood and latewood in the sapwood ofCryptomeria japonica.AbstractChanges over time in the cellular contents of xylem parenchyma cells provide important clues to the mechanism of the early events in the wound reaction of trees. In this study, we monitored the events that occur during the death of ray parenchyma cells after wounding. We examined nuclei, starch grains, and colored substances in ray parenchyma cells by light microscopy and the autofluorescence of cell walls of tracheids by confocal laser-scanning microscopy in Cryptomeria japonica after artificial wounding. In addition, we compared cytological changes in ray parenchyma cells in the longitudinal and radial directions. Finally, we analyzed the differences between earlywood and latewood in terms of the responses of ray parenchyma cells to wounding. Behind the wound, changes in cellular contents were visible first in latewood regions in the second annual ring behind the wound. The progression of changes in cellular contents of ray parenchyma cells stopped near the growth-ring boundary. These results indicate that the growth-ring boundary might prevent the spread of some factor(s) that induces cytological changes in ray parenchyma cells. Above the wound, most colored substances were localized in ray parenchyma cells that were located near wounds in latewood regions. Thus, even at an equal distance from the wound, the amount of secondary metabolites in ray parenchyma cells differed between earlywood and latewood. Our observations suggest that differences in the anatomical features of neighboring tracheids between earlywood and latewood might influence changes in cellular contents of ray parenchyma cells during reactions to wounding in Cryptomeria japonica.

The timing of latewood formation determines the genetic variation of wood density in Larix kaempferi

Key messageThe seasonal change of the wood formation stage, especially the timing of the cessation of cell division, are key to understanding the genetic difference of wood density.AbstractWood density is important in terms of various wood properties and forest carbon sequestration properties. Wood density is genetically variable, although the mechanism that causes this variability is not well clarified. We hypothesized that wood formation dynamics differ genetically and that this affects wood density. We analyzed the dynamics of wood formation, including the timing of earlywood-latewood transition and the cessation of cell division, and their relationship to clonal differences in wood density using nine clones of Larix kaempferi, through microscopy observations and X-ray densitometry. Wood density showed a strong correlation with the proportion of latewood. The clonal variation of the timing of the earlywood-latewood transition was small. The timing of the cessation of cell division differed clonally by a maximum of 42.7 days and was correlated with the duration of latewood formation. The duration of latewood formation showed a correlation coefficient of 0.925 with the proportion of latewood. We described a hierarchical relationship that explained the genetic difference in wood density in mature L. kaempferi wood in the following sequence; the timing of cessation of latewood formation, the duration of latewood formation, the proportion of latewood, and wood density.