title: The impact of light intensity on shade-induced leaf senescence.
abstract: 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.
authors.affiliation: Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, S-90187 Umeå, Sweden.
authors.forename: Bastiaan
authors.initials: B
authors.lastname: Brouwer
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Ziolkowska
authors.forename: Matthieu
authors.initials: M
authors.lastname: Bagard
authors.forename: Olivier
authors.initials: O
authors.lastname: Keech
authors.forename: Per
authors.initials: P
authors.lastname: Gardeström
mesh_terms: D000064:Acclimatization; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics; D019069:Cell Respiration; D002734:Chlorophyll / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008027:Light; D046529:Microscopy, Electron, Transmission; D010788:Photosynthesis; D051942:Phytochrome A / Q000235:genetics; D018515:Plant Leaves / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; D002734:Chlorophyll