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Shedding Light on Shade- and Dark-Induced Leaf Senescence

Brouwer, Bastiaan, 1980- (author)
Umeå universitet,Institutionen för fysiologisk botanik,Umeå Plant Science Centre (UPSC),Per Gardeström
Gardeström, Per (thesis advisor)
Umeå universitet,Institutionen för fysiologisk botanik,Umeå Plant Science Centre (UPSC)
Krupinska, Karin, Professor (opponent)
Christian-Albrechts-Universität zu Kiel, Botanisches Institute und Botanischer Garten
 (creator_code:org_t)
ISBN 9789174594379
Umeå : KBC, Umeå University, 2012
English 52 s.
  • Doctoral thesis (other academic/artistic)
Abstract Subject headings
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  • 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.

Subject headings

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)
NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

Keyword

Arabidopsis
darkness
light
photosynthesis
phytochrome
shade
senescence

Publication and Content Type

vet (subject category)
dok (subject category)

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