Abstract
The megagametophyte of mature seeds of Araucaria angustifolia consists of cells with thin walls, one or more nuclei, a central vacuole storing proteins, and a cytoplasm rich in amyloplasts, mitochondria and lipid bodies. In this study, we describe the process of mobilization of reserves and analyzed the dismantling of the tissue during germination, using a range of well-established markers of programmed cell death (PCD), including: morphological changes in nuclei and amyloplasts, DNA degradation, and changes in nuclease profiles. TUNEL reaction and DNA electrophoresis demonstrate that DNA fragmentation in nuclei occurs at early stages of germination, which correlates with induction of specific nucleases. The results of the present study add knowledge on the dismantling of the megagametophyte of genus Araucaria, a storage tissue that stores starch as the main reserve substance, as well as on the PCD pathway, by revealing new insights into the role of nucleases and the expression patterns of putative nuclease genes during germination.
Highlights
In seeds of both Gymnosperms and Angiosperms, stored nutrients must be mobilized to support germination and early seedling growth (Young and Gallie, 2000a; Bewley et al, 2013)
DNA fragmentation accompanied the progressive cellular changes observed in the cells of the megagametophyte
On the basis of these results, we propose that the pathway of cell death in the A. angustifolia megagametophyte is programmed cell death (PCD)
Summary
In seeds of both Gymnosperms and Angiosperms, stored nutrients must be mobilized to support germination and early seedling growth (Young and Gallie, 2000a; Bewley et al, 2013). The main seed storage tissues, i.e., the endosperm, the perisperm, or both (in Angiosperms), and the megagametophyte (in Gymnosperms), undergo programmed cell death (PCD) In Angiosperms, the mobilization of lipids and proteins from lipid and protein bodies during germination has been studied in seeds of several species. For example, it is well documented that cells of the aleurone layer lack a central vacuole and store proteins and lipids in protein vacuoles and lipid bodies, respectively. In Gymnosperms, to date, the cell death of the megagametophyte during the mobilization of reserves is understudied and the process has been described only in Araucaria bidwillii (Casani et al, 2009) and Picea glauca (He and Kermode, 2003)
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