Journal
PROTOPLASMA
Volume 213, Issue 1-2, Pages 99-107Publisher
SPRINGER-VERLAG WIEN
DOI: 10.1007/BF01280510
Keywords
Arabidopsis thaliana; apoptosis; plasmodesmata; root cap; root apical meristem; root development
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Plasmodesmata frequency and distribution in root cap cells of Arabidopsis thaliana root tips were characterized during four weeks after germination to understand the symplasmic control of apoptosis. Apoptotic cells in some of the root apical-meristem cells and in root cap cells were identified by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling reaction and characterized by electron microscopy. Starting at the second week after germination, cells in the outermost layers of the root cap showed typical apoptotic features, including nuclear DNA fragmentation, chromatin condensation, cytoplasmic vacuolation, and organelle destruction. Intercellular connections, indicated by the frequency and number of plasmodesmata per cell length, were significantly reduced in the walls of outer root cap cells. This shows that cells become symplasmically isolated during the apoptosis process. In apoptotic root cap cells, the majority of nonfunctional plasmodesmata were observed to be associated with degenerated endoplasmic reticulum: this state was prior to the detection of any nuclear DNA fragmentation. Other nonfunctional plasmodesmata were sealed by heterogeneous cell wall materials. However, in immature epidermal and cortical cells in ii-week-old arrested roots the endoplasmic reticulum associated with plasmodesmata became disconnected as a result of protoplast condensation and shrinkage. No degenerated endoplasmic reticulum was observed in these cells. These observations suggest that the apoptotic processes in the root body and the root cap are different.
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