Differences in patterns of cell death between ray parenchyma cells and ray tracheids in the conifers Pinus densiflora and Pinus rigida

Abstract

Differences in patterns of cell death between ray parenchyma cells and ray tracheids in the conifers Pinus densiflora and Pinus rigida were clarified. Differentiation and cell death of ray tracheids occurred successively and both were related to the distance from the cambium. In this respect, they resembled those of longitudinal tracheids. Thus, the cell death of short-lived ray tracheids could be characterized as time-dependent programmed cell death. In contrast, ray parenchyma cells survived for several years or more, and no successive cell death occurred, even within a single radial line of cells in a ray. Thus, the features of death of the ray parenchyma cells were different from those of ray tracheids. Cell death occurred early in ray parenchyma cells that were in contact with ray tracheids. The initiation of secondary wall thickening occurred earlier in ray parenchyma cells that were in contact with ray tracheids in Pinus densiflora than in others. In addition, localized thickening of secondary walls occurred only in ray parenchyma cells that were in contact with ray tracheids in Pinus rigida. Moreover, no polyphenols were evident in such cells in either species. Therefore, ray parenchyma cells that were in contact with ray tracheids appeared not to play a role in the formation of heartwood extractives. Our observations indicate that short-lived ray tracheids might affect the pattern of differentiation and, thus, the functions of neighboring longlived ray parenchyma cells in conifers.

Lignification of ray parenchyma cells (RPCs) in the xylem of Phellodendron amurense Rupr.: quantitative and structural investigation by TOF-SIMS and thioacidolysis of laser microdissection cuts of RPCs

“…In analogy to our previous study on a softwood (Zheng et al 2014a,b) it can be presumed that RPCs of hardwoods are also more lignified in hW than in sW. Nakaba et al (2008Nakaba et al ( , 2012 reported that the number of dead RPCs in sW increased from the cambium side towards the pith in both softwood and hardwood. In the TZ, the number of dead RPCs increased rapidly, and almost all of the RPCs were dead in the hW.…”

“…Lignification and the structure of the cell wall in different types of RPCs in Populus maximowiczii Henry were compared by Murakami et al (1999) by means of the UV microscopy, POM, and TEM. The pattern of cell death, the process of lignification, and the function of RPCs in several species of both softwood and hardwood species were studied by Nakaba et al (2006Nakaba et al ( , 2008Nakaba et al ( , 2012 by means of microscopy.…”

Concentration and Distribution of Nuclei and Plastids in Xylem Cells in Cunninghamia lanceolata and Aquilaria sinensis

“…Some of ray parenchyma cells and axial parenchyma cells contained nuclei and plastids, because these cells survived longer when compared to other cells, such as fiber, tracheary elements, and vessels. (Abe et al 2011;Nakaba et al 2006;Nakaba et al 2008). Xylem was formed after PCD.…”

Heterologous hybridisation to a Pinus microarray: profiling of gene expression in Pinus radiata saplings exposed to ethephon

“…When comparing different studies it is important to understand the influence of the composition of the woody portion of the stem from which the RNA is extracted. This RNA from woody tissues is expected to comprise primarily of RNA from the outermost layer of woody differentiating xylem, since the final autolysis of cellular contents is slow in conifer tracheids (Bollhöner et al 2012) but it will also contain RNA from rays and resin duct parenchyma, as the latter can live for more than 30 years in Pinus (Nakaba et al 2008). The xylem transcriptomes obtained from the 2-year-old saplings used in this study likely reflect developmentally young, but woody, outer xylem seen immediately below the gelatinous 'developing xylem' of older trees.…”