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Gene expression in autumn leaves
Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
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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.

Place, publisher, year, edition, pages
2003. Vol. 131, no 2, 430-442 p.
URN: urn:nbn:se:umu:diva-5064DOI: 10.1104/pp.012732PubMedID: 12586868OAI: diva2:144425
Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2015-04-29Bibliographically approved
In thesis
1. Constructing a timetable of autumn senescence in aspen
Open this publication in new window or tab >>Constructing a timetable of autumn senescence in aspen
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.
Populus tremula, autumn senescence, senescence-associated genes, cellular timetable, transcriptional timetable, cDNA microarrays, EST sequencing
National Category
urn:nbn:se:umu:diva-752 (URN)91-7264-075-8 (ISBN)
Public defence
2006-05-05, KB3B1, KBC-huset, universitetsområdet, Umeå, 10:00
Available from: 2006-04-12 Created: 2006-04-12Bibliographically approved

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Bhalerao, RupaliKeskitalo, JohannaBirve, Simon JonssonKarlsson, JanGardeström, PerGustafsson, PetterJansson, Stefan
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