Eitaro Fukatsu

Changes in Morphology, Anatomy, and Photosynthetic Capacity of Needles of Japanese Larch (Larix kaempferi) Seedlings Grown in High CO2 Concentrations

Photosynthetic traits of two-year-old Japanese larch seedlings (Larix kaempferi Carr.) grown at elevated CO2 concentrations were studied in relation to structural changes in the needles. Seedlings were grown at two CO2 concentrations, 360 (AC) and 720 (EC) μmol mol−1 at high and low nutrient supply rates, high N (HN) and low N (LN). The photosynthetic capacity fell significantly in EC+LN, but increased significantly in EC+HN. Since the mesophyll surface area exposed to intercellular space per unit leaf area (Ames/A) is correlated with the photosynthetic rate, we measured Ames/A for larch needles growing in EC. Changes of Ames/A in both EC+HN and EC+LN were very similar to the changes in photosynthetic capacity. This suggests that the changes of Ames/A in EC probably caused the changes in the photosynthetic capacity. The changes of Ames/A in EC were attributed to changes in the mesophyll cell size and mesophyll cell number. The photosynthetic capacity in EC can be explained by taking morphological and structural adaptations into account as well as biochemical factors.

Involvement of Localized Cortical Microtubules in the Formation of a Modified Structure of Wood

Cambial cells dierentiate into secondary xylem cells through a process of expansion or elongation, cell wall thickening, cell wall sculpturing, lignification, and cell death (formation of wood). The secondary xylem cells develop modifications of the cell wall such as pits, helical thickenings, perforations and warts, through the localized deposition of cell wall materials. Recent observations have revealed that the localized appearance or disappearance of cortical microtubules is related to the localized deposition of cellulose microfibrils in secondary xylem cells. Cortical microtubules play an important role in the morphogenesis of secondary xylem cells, thereby controlling the structure of wood. Therefore, cortical microtubules provide a target for biotechnological applications to change the quality of wood.

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.

Mesophyll conductance in leaves of Japanese white birch (Betula platyphylla var. japonica) seedlings grown under elevated CO2 concentration and low N availability

To test the hypothesis that mesophyll conductance (gm ) would be reduced by leaf starch accumulation in plants grown under elevated CO2 concentration [CO2 ], we investigated gm in seedlings of Japanese white birch grown under ambient and elevated [CO2 ] with an adequate and limited nitrogen supply using simultaneous gas exchange and chlorophyll fluorescence measurements. Both elevated [CO2 ] and limited nitrogen supply decreased area-based leaf N accompanied with a decrease in the maximum rate of Rubisco carboxylation (Vc,max ) on a CO2 concentration at chloroplast stroma (Cc ) basis. Conversely, only seedlings grown at elevated [CO2 ] under limited nitrogen supply had significantly higher leaf starch content with significantly lower gm among the treatment combinations. Based on a leaf anatomical analysis using microscopic photographs, however, there were no significant difference in the area of chloroplast surfaces facing intercellular space per unit leaf area among treatment combinations. Thicker cell walls were suggested in plants grown under limited N by increases in leaf mass per area subtracting non-structural carbohydrates. These results suggest that starch accumulation and/or thicker cell walls in the leaves grown at elevated [CO2 ] under limited N supply might hinder CO2 diffusion in chloroplasts and cell walls, which would be an additional cause of photosynthetic downregulation as well as a reduction in Rubisco activity related to the reduced leaf N under elevated [CO2 ].

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.

Potential of Genome-Wide Studies in Unrelated Plus Trees of a Coniferous Species, Cryptomeria japonica (Japanese Cedar)

A genome-wide association study (GWAS) was conducted on more than 30,000 single nucleotide polymorphisms (SNPs) in unrelated first-generation plus tree genotypes from three populations of Japanese cedar Cryptomeria japonica D. Don with genomic prediction for traits of growth, wood properties and male fecundity. Among the assessed populations, genetic characteristics including the extent of linkage disequilibrium (LD) and genetic structure differed and these differences are considered to be due to differences in genetic background. Through population-independent GWAS, several significant SNPs found close to the regions associated with each of these traits and shared in common across the populations were identified. The accuracies of genomic predictions were dependent on the traits and populations and reflected the genetic architecture of traits and genetic characteristics. Prediction accuracies using SNPs selected based on GWAS results were similar to those using all SNPs for several combinations of traits and populations. We discussed the application of genome-wide studies for C. japonica improvement.