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Autophagic programmed cell death in the suspensor and endosperm of Vicia faba: An ultrastructural study
Stockholm University, Faculty of Science, Department of Botany.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Programmed cell death (PCD) is a widely spread phenomenon among multi-cellular organisms. Without the deletion of cells no longer needed, the organism will not be able to develop in a predicted way. It is now belived that all cells have the capacity to self-destruct and that the survival of the cells is depending on the repression of this suicidal programme. PCD has turned out to show similarities in many different species and there are strong indications that the mechanisms running the programme might, at least in some parts, be evolutionarily conserced. PCD is a generic term for different programmes of cell destruction, such as apoptosis and autophagic PCD. An important tool to determine if a cell is undergoing PCD is the transmitting electron microscope.

The aims of my study were to find out if, and in what way, the suspensor and endosperm in Vicia faba (Broad bean), which are short-lived structures, undergoes PCD. The endosperm degradation preceed the suspensor cell death and they differ to some extent ultrastructurally. The cell death occurs in both tissues about 13-14 days after pollination when the embryo proper is mature enough to support itself. It was found that both tissues are committed to autophagic PCD, a cell death characteristic of conspicuous formations of autophagic vacuoles. It was shown by histochemical staining that acid phosphatases are accumulated in these vacuoles but are also present in the cytoplasm. These vacuoles are similar to autophagic vacuoles formed in rat liver cells, indicating that autophagy is a widely spread phenomenon. DNA fragmentation is the first visible sign of PCD in both tissues and it is demonstrated by a labelling technique (TUNEL). In the endosperm nuclei the heterochromatin subsequently appears in the form of a network, while in the suspensor it is more conspicuous, with heterochromatin that forms large electron dense aggregates located close to the nuclear envelope.

In the suspensor, the plastids develop into chromoplasts with lycopene crystals at the same time or shortly after DNA fragmentation. This is probably due to the fact that the suspensor plastids function as hormone producing organelles and support the embryo proper with indispensable growth factors. Later the embryo will be able to produce its own growth factors and the synthesis of these, in particular gibberelines, might be suppressed in the suspensor. The precursors can then be used for synthesis of lycopene instead.

Both the suspensor and endosperm are going through autophagic PCD, but the process differs in some respects. This is probably due the the different function of the two tissues, and that the signals that trigger the process presumably are different. The embryo proper is probably the source of the death signal affecting the suspensor. The endosperm, which has a different origin and function, might be controlling the death signal within its own cell. The death might in this case be related to the age of the cell.

Place, publisher, year, edition, pages
Stockholm: Botaniska institutionen , 2004. , 38 p.
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:su:diva-123ISBN: 91-7265-893-2 (print)OAI: oai:DiVA.org:su-123DiVA: diva2:189649
Public defence
2004-05-19, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00
Opponent
Supervisors
Available from: 2004-04-28 Created: 2004-04-28Bibliographically approved
List of papers
1. DNA fragmentaion and nuclear degradation during programmed cell death in the suspensor and endosperm of Vicia faba
Open this publication in new window or tab >>DNA fragmentaion and nuclear degradation during programmed cell death in the suspensor and endosperm of Vicia faba
2001 (English)In: International journal of plant sciences, ISSN 1058-5893, E-ISSN 1537-5315, Vol. 162, no 5, 1053-1063 p.Article in journal (Refereed) Published
Abstract [en]

In Vicia faba, both the suspensor and the endosperm are short‐lived structures. The aim of this work was to elucidate and compare programmed cell death (PCD) mechanisms in these two ephemeral tissues. To achieve this, we used the TdT‐mediated dUDP fluorescent (FITC) nick end labeling (TUNEL) technique to trace DNA fragmentation and transmission electron microscopy to follow chromosomal and nuclear degradation. The TUNEL experiments demonstrated DNA fragmentation in the endosperm nuclei 13 d after pollination (dap) and in the suspensor at 14 dap. However, the ultrastructural studies did not show any chromosomal degradation in the nuclei of the suspensor or endosperm until 17 dap, indicating that the DNA fragmentation is an initial step in the PCD pathway. We have further documented fundamental differences in the degeneration process of the nuclei of the two tissues. In the suspensor the heterochromatin becomes more condensed during degeneration and disperses to the nuclear periphery as electron‐dense areas. The nucleolus will keep its round and condensed shape for some time before expanding into an irregular body. In the endosperm the heterochromatin is more like a network throughout the nucleus, and the nucleolus will eventually split into pieces scattered inside the heterochromatin. Internal vesicle‐like structures appear in the nuclei of the suspensor at 11–13 dap. However, they might have a communicative function not necessarily related to the cell death. We conclude that both the suspensor and the endosperm go through PCD processes, but the pathways leading to dismantling of the cells do not follow identical routes in the two tissues. DNA fragmentation occurs in intact cells and within an intact nuclear envelope and not in cells that already are damaged. PCD in the endosperm precedes PCD in the suspensor, indicating that they might receive different signals or that the signal triggers different internal death programs in the two tissues.

Keyword
DNA fragmentation, endosperm, nucleus, programmed cell death, suspensor
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-22863 (URN)10.1086/321922 (DOI)
Note
Part of urn:nbn:se:su:diva-123Available from: 2004-04-28 Created: 2004-04-28 Last updated: 2017-12-13Bibliographically approved
2. The formation of autophagic vacuoles during programmed cell death in the suspensor and endosperm of Vicia faba
Open this publication in new window or tab >>The formation of autophagic vacuoles during programmed cell death in the suspensor and endosperm of Vicia faba
(English)In: International journal of plant sciences, ISSN 1058-5893, E-ISSN 1537-5315Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:su:diva-22864 (URN)
Note
Part of urn:nbn:se:su:diva-123Available from: 2004-04-28 Created: 2004-04-28 Last updated: 2017-12-13Bibliographically approved
3. Chromoplasts are formed in Vicia faba suspensor cells
Open this publication in new window or tab >>Chromoplasts are formed in Vicia faba suspensor cells
2000 (English)In: International journal of plant sciences, ISSN 1058-5893, E-ISSN 1537-5315, Vol. 161, no 5, 713-719 p.Article in journal (Refereed) Published
Abstract [en]

In Vicia faba, the plastids of the suspensor have a structure that is unique for this tissue. Their development was followed from 4 to 15 days after pollination (dap), when the suspensor has started to degenerate. The appearence of the plastids changes from small and rounded to large and more or less amoeboid. A distinct peripheral reticulum and ribosomes are present throughout plastid development. At 11 dap, most plastids have formed one or more prolamellar bodies. After zinc iodide-osmium tetroxide staining, the plastids also show strongly electron-scattering bundles of membrane tubules, sometimes with cross-linking between individual thylakoids. At 13-14 dap, the thylakoid system includes large electron-transparent spaces that are traversed by undulating membranes. Such a structure is characteristic of chromoplasts containing carotenoid crystals. In the light microscope, crystals are seen as bright red inclusions in the plastids.

National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-22865 (URN)
Available from: 2004-04-28 Created: 2004-04-28 Last updated: 2017-12-13Bibliographically approved
4. Ultrastructural study of mitochondria during programmed cell death in vicia
Open this publication in new window or tab >>Ultrastructural study of mitochondria during programmed cell death in vicia
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-22866 (URN)
Note
Part of urn:nbn:se:su:diva-123Available from: 2004-04-28 Created: 2004-04-28 Last updated: 2010-01-13Bibliographically approved

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