Differences in patterns of cell death between ray parenchyma cells and ray tracheids in the conifers <Emphasis Type="Italic">Pinus densiflora</Emphasis> and <Emphasis Type="Italic">Pinus rigida</Emphasis> |
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Authors: | Satoshi Nakaba Takafumi Kubo Ryo Funada |
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Institution: | (1) Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu Tokyo, 183-8509, Japan |
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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 long-lived ray parenchyma
cells in conifers. |
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Keywords: | Cell death Heartwood formation Ray parenchyma cell Ray tracheid Xylem differentiation |
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