Distribution of Living Ray Parenchyma Cells and Major Bioactive Compounds During the Heartwood Formation of Taiwania cryptomerioides Hayata

Differential Gene Profiling of the Heartwood Formation Process in Taiwania cryptomerioides Hayata Xylem Tissues

“…HW formation has been suggested as a special type of tissue senescence, and the PCD of ray parenchyma cells during HW formation shares some similarity to the PCD of xylem tracheary elements (TEs) [3,15,39]. In Taiwania's TZ, ray parenchyma cells gradually lose their vitality (Figure 1b) and cellular contents [17]. DEGs encoding nucleases and vacuolar processing enzyme (VPE) were highly expressed in TZ with about 8-to 85-fold changes compared to SW-1 or SW-2 ( Figure 9; Table S6).…”

“…Similar results were reported in conifer and hardwood species, such as P. sylvestris (Scots pine), J. nigra (black walnut), and R. pseudoacacia (black locust), that the transcription levels of genes related to the biosynthesis of phenolic or flavonoid compounds were correlated with the accumulation of HW extractives in the TZ of these species [22,25,27]. In Taiwania, the starch grains were deposited in the ray parenchyma cells of SW-2, and the ray parenchyma cells would gradually lose their nuclei and starch grains in the TZ region, where the deposition of colored extractives started [17]. Higher-expressed starch-degrading genes are likely related to the degradation of starch to provide the carbon source for the biosynthesis of the bioactive compounds, and the expression of nuclease-encoding genes toward TZ may be related to the degradation of nuclei in the ray parenchyma cells.…”

“…The distribution of living ray parenchyma cells, total extractive content, and major bioactive compounds were profiled as per Chen et al [17]. Briefly, the increment cores were separated ring by ring into different segments from cambium to HW, and these segments were cryostat-sectioned (Leica CM1900) at −20 • C to obtain the radial sections (40 µm in thickness).…”

“…HW formation is described as a form of programmed cell death [15], and it has been suggested that the longevity of the ray parenchyma cells and the depletion of reserve materials are closely related to the HW formation process [3,16]. Previous research has shown that the ray parenchyma cells of Taiwania gradually lose the starch grains from the inner SW and lose their nuclei in TZ, whereas the colored substances deposit into the cell lumens in the TZ [17]. Overall, the ray parenchyma cells lose their vitality within 1-2 annual rings in the TZ, which would appear between [8][9][10][11][12][13] year rings counted from the cambium, depending on individual trees [17].…”

“…Overall, the ray parenchyma cells lose their vitality within 1-2 annual rings in the TZ, which would appear between [8][9][10][11][12][13] year rings counted from the cambium, depending on individual trees [17]. Similar results were also reported for other species, and the occurrence of this TZ is species-dependent, with the year ring numbers from cambium being 7-8 in Larix kaempferi [18], [12][13][14][15][16][17][18][19][20][21][22][23] in Cryptomeria japonica [19], and 14-22 and 28-33 in Pinus rigida and Pinus densiflora [20]. The extractives often start to accumulate from inner SW, increase in TZ, and deposit to a high level in the HW region [17,20,21].…”