title: Chlorophyll breakdown in senescent Arabidopsis leaves. Characterization of chlorophyll catabolites and of chlorophyll catabolic enzymes involved in the degreening reaction.
abstract: During senescence, chlorophyll (chl) is metabolized to colorless nonfluorescent chl catabolites (NCCs). A central reaction of the breakdown pathway is the ring cleavage of pheophorbide (pheide) a to a primary fluorescent chl catabolite. Two enzymes catalyze this reaction, pheide a oxygenase (PAO) and red chl catabolite reductase. Five NCCs and three fluorescent chl catabolites (FCCs) accumulated during dark-induced chl breakdown in Arabidopsis (Arabidopsis thaliana). Three of these NCCs and one FCC (primary fluorescent chl catabolite-1) were identical to known catabolites from canola (Brassica napus). The presence in Arabidopsis of two modified FCCs supports the hypothesis that modifications, as present in NCCs, occur at the level of FCC. Chl degradation in Arabidopsis correlated with the accumulation of FCCs and NCCs, as well as with an increase in PAO activity. This increase was due to an up-regulation of Pao gene expression. In contrast, red chl catabolite reductase is not regulated during leaf development and senescence. A pao1 knockout mutant was identified and analyzed. The mutant showed an age- and light-dependent cell death phenotype on leaves and in flowers caused by the accumulation of photoreactive pheide a. In the dark, pao1 exhibited a stay-green phenotype. The key role of PAO in chl breakdown is discussed.
authors.affiliation: Institute of Plant Sciences, University of Bern, Switzerland.
authors.forename: Adriana
authors.initials: A
authors.lastname: Pruzinská
authors.forename: Gaby
authors.initials: G
authors.lastname: Tanner
authors.forename: Sylvain
authors.initials: S
authors.lastname: Aubry
authors.forename: Iwona
authors.initials: I
authors.lastname: Anders
authors.forename: Simone
authors.initials: S
authors.lastname: Moser
authors.forename: Thomas
authors.initials: T
authors.lastname: Müller
authors.forename: Karl-Hans
authors.initials: KH
authors.lastname: Ongania
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kräutler
authors.forename: Ji-Young
authors.initials: JY
authors.lastname: Youn
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Liljegren
authors.forename: Stefan
authors.initials: S
authors.lastname: Hörtensteiner
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism; D016923:Cell Death; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008027:Light; D015394:Molecular Structure; D016254:Mutagenesis, Insertional / Q000235:genetics; D010088:Oxidoreductases / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D018515:Plant Leaves / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism*; D013997:Time Factors
chemical_list: D051017:Apoptosis Regulatory Proteins; D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; C036483:T-DNA; D002734:Chlorophyll; D010088:Oxidoreductases; D010105:Oxygenases; C112915:pheide a oxygenase; C408689:ACD2 protein, Arabidopsis