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Shedding Light on Shade- and Dark-Induced Leaf Senescence
Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). (Per Gardeström)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Leaf senescence is the final stage of leaf development, during which the leaf relocates most of itsvaluable nutrients to developing or storing parts of the plant. As this process progresses, leaves losetheir green color and their capacity to perform photosynthesis. Shade and darkness are well-knownas factors inducing leaf senescence and it has been proposed that senescence can be initiated byreductions in photosynthesis, photomorphogenesis and transpiration. However, despite the fact thatthe signaling mechanisms regulating each of these processes have been extensively described,particularly in seedlings, their contribution to the initiation of senescence in mature leaves stillremains unclear. Furthermore, the use of different experimental systems to study shade-inducedleaf senescence has yielded several divergent results, which altogether complicate the overallunderstanding of leaf senescence.

To address this, darkened plants and individually darkened leaves, which show different rates of leafsenescence, were studied. Comparing the transcriptome and metabolome of these two darktreatmentsrevealed that they differed distinctly with regard to their metabolic strategies. Wholedarkened plants were severely carbohydrate-starved, accumulated amino acids and slowed downtheir metabolism. In contrast, individually darkened leaves showed continued active metabolismcoupled to senescence-associated degradation and relocation of amino acids.

This knowledge was used to set up a new system to study how shade affects leaf senescence in themodel plant Arabidopsis thaliana. Use of this system revealed that different senescence-associatedhallmarks appeared in response to different intensities of shade. Some of these hallmarks werefurther shown to be part of both leaf senescence and photosynthetic acclimation to low light.

Finally, using this system on phytochrome mutants revealed that loss of phytochrome A increasedthe loss of chlorophyll under shade, without increasing the expression of senescence-associatedgenes.

Together, these findings suggest that shade-induced leaf senescence, which is generally perceived asa single process, is actually an intricate network of different processes that work together tomaintain an optimal distribution of nutrients within the plant.

Place, publisher, year, edition, pages
Umeå: KBC, Umeå University , 2012. , 52 p.
Keyword [en]
Arabidopsis, darkness, light, photosynthesis, phytochrome, shade, senescence
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-54636ISBN: 978-91-7459-437-9 (print)OAI: oai:DiVA.org:umu-54636DiVA: diva2:524646
Public defence
2012-05-25, KB3A9, KBC-huset, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2012-05-04 Created: 2012-05-03 Last updated: 2015-04-29Bibliographically approved
List of papers
1. Comparison between leaves from darkened plants and individually-darkened leaves reveals differential metabolic strategies in response to darkness
Open this publication in new window or tab >>Comparison between leaves from darkened plants and individually-darkened leaves reveals differential metabolic strategies in response to darkness
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(English)Manuscript (preprint) (Other academic)
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-54631 (URN)
Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2012-05-04
2. The impact of light intensity on shade-induced leaf senescence
Open this publication in new window or tab >>The impact of light intensity on shade-induced leaf senescence
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2012 (English)In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 35, no 6, 1084-1098 p.Article in journal (Refereed) Published
Abstract [en]

Plants often have to cope with altered light conditions, which in leaves induce various physiological responses ranging from photosynthetic acclimation to leaf senescence. However, our knowledge of the regulatory pathways by which shade and darkness induce leaf senescence remains incomplete. To determine to what extent reduced light intensities regulate the induction of leaf senescence, we performed a functional comparison between Arabidopsis leaves subjected to a range of shading treatments. Individually covered leaves, which remained attached to the plant, were compared with respect to chlorophyll, protein, histology, expression of senescence-associated genes, capacity for photosynthesis and respiration, and light compensation point (LCP). Mild shading induced photosynthetic acclimation and resource partitioning, which, together with a decreased respiration, lowered the LCP. Leaf senescence was induced only under strong shade, coinciding with a negative carbon balance and independent of the red/far-red ratio. Interestingly, while senescence was significantly delayed at very low light compared with darkness, phytochrome A mutant plants showed enhanced chlorophyll degradation under all shading treatments except complete darkness. Taken together, our results suggest that the induction of leaf senescence during shading depends on the efficiency of carbon fixation, which in turn appears to be modulated via light receptors such as phytochrome A.

Place, publisher, year, edition, pages
Malden, MA: Wiley-Blackwell, 2012
Keyword
Arabidopsis thaliana, light compensation point (LCP), photosynthetic acclimation, photosynthetic resource partitioning, phytochromeA (PHYA), R/FR ratio
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-54633 (URN)10.1111/j.1365-3040.2011.02474.x (DOI)000303052500007 ()
Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2017-12-07Bibliographically approved
3. Far-red light reduces senescence-associated chlorophyll loss under low light via a Phytochrome A-mediated Far-red High Irradiance Response
Open this publication in new window or tab >>Far-red light reduces senescence-associated chlorophyll loss under low light via a Phytochrome A-mediated Far-red High Irradiance Response
(English)Manuscript (preprint) (Other academic)
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-54635 (URN)
Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2012-05-04

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Brouwer, Bastiaan

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