umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Constructing a timetable of autumn senescence in aspen
Umeå University, Faculty of Science and Technology, Plant Physiology.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During the development and lifecycle of multicellular organisms, cells have to die, and this occurs by a process called programmed cell death or PCD, which can be separated from necrosis or accidental cell death (Pennell and Lamb, 1997). Senescence is the terminal phase in the development of an organism, organ, tissue or cell, where nutrients are remobilized from the senescing parts of the plant into other parts, and the cells of the senescing organ or tissue undergo PCD if the process is not reversed in time. Leaf senescence involves cessation of photosynthesis, loss of pigments and proteins, nutrient remobilization, and degradation of the plant cells (Smart, 1994). Initiation of leaf senescence is triggered by a wide range of endogenous and environmental factors, that through unknown pathways controls the process, and regulates the expression of senescence-associated genes (SAGs) (Buchanan-Wollaston, 1997). Autumn leaf senescence in deciduous trees is regulated by photoperiod and temperature, and is an attractive experimental system for studies on senescence in perennial plants.

We have studied the process of autumn senescence in a free-growing aspen (Populus tremula) by following changes in pigment, metabolite and nutrient content, photosynthesis, and cell and organelle integrity. All data were combined in a cellular timetable of autumn senescence in aspen. The senescence process started on September 11 with degradation of pigments and other leaf constituents, and once initiated, progressed steadily without being affected by the environment. Chloroplasts were rapidly degraded, and mitochondria took over energy production after chlorophyll levels had dropped by 50%. At the end of remobilization, around 29th of September, some cells were still metabolically active and had chlorophyll-containing plastids. Over 80% of nitrogen and phosphorus was remobilized, and a sudden change in the 15N of the cellular content on September 29, indicated that volatile compounds may have been released.

We have also studied gene expression in autumn leaves by analysing EST sequences from two different cDNA libraries, one from autumn leaves of a field-grown aspen and the other from young, but fully expanded leaves of a green-house grown aspen. In the autumn leaf library, ESTs encoding metallothioneins, proteases, stress-related proteins and proteins involved in respiration and breakdown of macromolecules were abundant, while genes coding for photosynthetic proteins were massively downregulated. We have also identified homologues to many known senescence-associated genes in annual plants.

By using Populus cDNA microarrays, we could follow changes in gene expression during the autumn over four years in the same free-growing aspen tree. We also followed changes in chlorophyll content to monitor the progression of leaf senescence. We observed a major shift in gene expression, occuring at different times the four years, that reflected a metabolic shift from photosynthetic competence to energy generation by mitochondrial respiration. Even though autumn senescence was initiated almost at the same date each year, the transcriptional timetables were different from year to year, especially for 2004, which indicates that there is no strict correlation between the transcriptional and the cellular timetables of leaf senescence.

Place, publisher, year, edition, pages
Umeå: Fysiologisk botanik , 2006. , 30 p.
Keyword [en]
Populus tremula, autumn senescence, senescence-associated genes, cellular timetable, transcriptional timetable, cDNA microarrays, EST sequencing
National Category
Botany
Identifiers
URN: urn:nbn:se:umu:diva-752ISBN: 91-7264-075-8 (print)OAI: oai:DiVA.org:umu-752DiVA: diva2:144429
Public defence
2006-05-05, KB3B1, KBC-huset, universitetsområdet, Umeå, 10:00
Opponent
Supervisors
Available from: 2006-04-12 Created: 2006-04-12Bibliographically approved
List of papers
1. Gene expression in autumn leaves
Open this publication in new window or tab >>Gene expression in autumn leaves
Show others...
2003 (English)In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 131, no 2, 430-442 p.Article in journal (Refereed) Published
Abstract [en]

Two cDNA libraries were prepared, one from leaves of a field-grown aspen (Populus tremula) tree, harvested just before any visible sign of leaf senescence in the autumn, and one from young but fully expanded leaves of greenhouse-grown aspen (Populus tremula x tremuloides). Expressed sequence tags (ESTs; 5,128 and 4,841, respectively) were obtained from the two libraries. A semiautomatic method of annotation and functional classification of the ESTs, according to a modified Munich Institute of Protein Sequences classification scheme, was developed, utilizing information from three different databases. The patterns of gene expression in the two libraries were strikingly different. In the autumn leaf library, ESTs encoding metallothionein, early light-inducible proteins, and cysteine proteases were most abundant. Clones encoding other proteases and proteins involved in respiration and breakdown of lipids and pigments, as well as stress-related genes, were also well represented. We identified homologs to many known senescence-associated genes, as well as seven different genes encoding cysteine proteases, two encoding aspartic proteases, five encoding metallothioneins, and 35 additional genes that were up-regulated in autumn leaves. We also indirectly estimated the rate of plastid protein synthesis in the autumn leaves to be less that 10% of that in young leaves.

Identifiers
urn:nbn:se:umu:diva-5064 (URN)10.1104/pp.012732 (DOI)12586868 (PubMedID)
Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2015-04-29Bibliographically approved
2. A transcriptional timetable of autumn senescence
Open this publication in new window or tab >>A transcriptional timetable of autumn senescence
Show others...
2004 (English)In: Genome Biology, ISSN 1465-6906, E-ISSN 1474-760X, Vol. 5, no 4, R24- p.Article in journal (Refereed) Published
Abstract [en]

Background We have developed genomic tools to allow the genus Populus (aspens and cottonwoods) to be exploited as a full-featured model for investigating fundamental aspects of tree biology. We have undertaken large-scale expressed sequence tag (EST) sequencing programs and created Populus microarrays with significant gene coverage. One of the important aspects of plant biology that cannot be studied in annual plants is the gene activity involved in the induction of autumn leaf senescence. Results On the basis of 36,354 Populus ESTs, obtained from seven cDNA libraries, we have created a DNA microarray consisting of 13,490 clones, spotted in duplicate. Of these clones, 12,376 (92%) were confirmed by resequencing and all sequences were annotated and functionally classified. Here we have used the microarray to study transcript abundance in leaves of a free-growing aspen tree (Populus tremula) in northern Sweden during natural autumn senescence. Of the 13,490 spotted clones, 3,792 represented genes with significant expression in all leaf samples from the seven studied dates. Conclusions We observed a major shift in gene expression, coinciding with massive chlorophyll degradation, that reflected a shift from photosynthetic competence to energy generation by mitochondrial respiration, oxidation of fatty acids and nutrient mobilization. Autumn senescence had much in common with senescence in annual plants; for example many proteases were induced. We also found evidence for increased transcriptional activity before the appearance of visible signs of senescence, presumably preparing the leaf for degradation of its components.

Keyword
Aging/*genetics, Cell Death/genetics, Chronobiology/*genetics, DNA; Complementary/genetics, DNA; Plant/genetics, Expressed Sequence Tags, Gene Expression Profiling/methods, Gene Expression Regulation; Plant/genetics, Gene Library, Oligonucleotide Array Sequence Analysis/methods, Plant Leaves/genetics, Populus/cytology/genetics, RNA; Plant/genetics, Seasons, Sequence Analysis; DNA/methods, Transcription; Genetic/*genetics
Identifiers
urn:nbn:se:umu:diva-5065 (URN)15059257 (PubMedID)
Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2015-04-29Bibliographically approved
3. A cellular timetable of autumn senescence
Open this publication in new window or tab >>A cellular timetable of autumn senescence
2005 (English)In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 139, no 4, 1635-1648 p.Article in journal (Refereed) Published
Abstract [en]

We have studied autumn leaf senescence in a free-growing aspen (Populus tremula) by following changes in pigment, metabolite and nutrient content, photosynthesis, and cell and organelle integrity. The senescence process started on September 11, 2003, apparently initiated solely by the photoperiod, and progressed steadily without any obvious influence of other environmental signals. For example, after this date, senescing leaves accumulated anthocyanins in response to conditions inducing photooxidative stress, but at the beginning of September the leaves did not. Degradation of leaf constituents took place over an 18-d period, and, although the cells in each leaf did not all senesce in parallel, senescence in the tree as a whole was synchronous. Lutein and {beta}-carotene were degraded in parallel with chlorophyll, whereas neoxanthin and the xanthophyll cycle pigments were retained longer. Chloroplasts in each cell were rapidly converted to gerontoplasts and many, although not all, cells died. From September 19, when chlorophyll levels had dropped by 50%, mitochondrial respiration provided the energy for nutrient remobilization. Remobilization seemed to stop on September 29, probably due to the cessation of phloem transport, but, up to abscission of the last leaves (over 1 week later), some cells were metabolically active and had chlorophyll-containing gerontoplasts. About 80% of the nitrogen and phosphorus was remobilized, and on September 29 a sudden change occurred in the {delta}15N of the cellular content, indicating that volatile compounds may have been released.

Keyword
Anthocyanins/metabolism, Carotenoids/metabolism, Chlorophyll/metabolism, Chloroplasts/metabolism, Microscopy; Electron, Mitochondria/metabolism, Nitrogen/metabolism, Phosphorus/metabolism, Photobiology, Photoperiod, Photosynthesis, Pigments; Biological/metabolism, Plant Leaves/cytology/*growth & development/metabolism, Populus/cytology/*growth & development/metabolism, Seasons
Identifiers
urn:nbn:se:umu:diva-5066 (URN)doi:10.1104/pp.105.066845 (DOI)
Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2015-04-29Bibliographically approved
4. Autumn leaf senescence and gene expression changes
Open this publication in new window or tab >>Autumn leaf senescence and gene expression changes
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-5067 (URN)
Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2010-01-13Bibliographically approved

Open Access in DiVA

fulltext(720 kB)1290 downloads
File information
File name FULLTEXT01.pdfFile size 720 kBChecksum SHA-1
a2d498457f1765732f19c180f9159d5bfc16aa0f5047e08a4687bc1a21a0b606de112572
Type fulltextMimetype application/pdf

By organisation
Plant Physiology
Botany

Search outside of DiVA

GoogleGoogle Scholar
Total: 1290 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 600 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf