How Long Do Wood Parenchyma Cells Live in the Stem of a Scots Pine (Pinus sylvestris L.)? Studies on Cell Nuclei Status along the Radial and Longitudinal Stem Axes

Abstract

This paper deals with the spatial distribution of heartwood in Scots pine stems (Pinus sylvestris L.), determined on the basis of the absence of nuclei in parenchyma cells. Samples were collected at several heights from two Scots pine stems growing in fresh coniferous stand as codominant trees. Transverse and radial sections were cut from the samples and stained with acetocarmine to detect the nuclei and with I2KI to show starch grains. Unstained sections were also observed under ultraviolet (UV) light to reveal cell wall lignification. The shapes of the nuclei in ray and axial parenchyma cells differed: the axial parenchyma cells had rounded nuclei, while the nuclei of the ray parenchyma cells were elongated. The lifespan of the parenchyma cells was found to be 16–42 years; the longest-lived were cells from the base of the stem, and the shortest-lived were from the base of the crown. The largest number of growth rings comprising heartwood was observed at a height of 1.3–3.3 m, which signifies that the distribution of heartwood within the stem is uneven. Moreover, the distance of the cells from the apical meristem and the cambium was seen to have an effect on the presence of living parenchyma cells, i.e., those with stained nuclei.

Anatomical and Morphological Features of Scots Pine Heartwood Formation in Two Forest Types in the Middle Taiga Subzone

“…Thus, under the conditions of Karelia, the lifespan of the parenchyma cells is up to 45 years in the trunks of 70-80-year-old Scotch pine trees, regardless of the growing conditions [45]. Similar values of the lifespan of parenchyma cells for Scots pine trees at the age of 70-80 years were obtained by other authors [57,64,78].…”

“…Starch disappears from the parenchyma cells [56][57][58][59], which is confirmed by biochemical analyses [60][61][62][63]. The cell walls of the radial parenchyma are lignified [51,58,64]. The final stage in the sapwood transformation into heartwood is nuclei destruction and parenchyma cell death [56,58,64].…”

“…The cell walls of the radial parenchyma are lignified [51,58,64]. The final stage in the sapwood transformation into heartwood is nuclei destruction and parenchyma cell death [56,58,64].…”

Lignification and cell wall thickening of ray parenchyma cells in Scots pine sapwood

“…Anatomical descriptions of Pinus sylvestris define the ray parenchyma cells in the sapwood as thin-walled, unlignified cells (Grosser 1977). Lignification of parenchyma cells is commonly associated with the transition zone from sapwood to the heartwood (Bergström 2003. Tulik et al 2019, and not with sapwood areas close to the bark or earlier in the sapwood.…”

“…Ray parenchyma cells remain alive for several years, and the functionality of the cells can remain throughout the sapwood. (Spicer & Holbrook 2007;Tulik et al 2019).…”