title: Differences between winter oilseed rape (Brassica napus L.) cultivars in nitrogen starvation-induced leaf senescence are governed by leaf-inherent rather than root-derived signals.
abstract: Nitrogen (N) efficiency of winter oilseed rape (Brassica napus L.) line-cultivars (cvs.), defined as high grain yield under N limitation, has been primarily attributed to maintained N uptake during reproductive growth (N uptake efficiency) in combination with delayed senescence of the older leaves accompanied with maintained photosynthetic capacity (functional stay-green). However, it is not clear whether genotypic variation in N starvation-induced leaf senescence is due to leaf-inherent factors and/or governed by root-mediated signals. Therefore, the N-efficient and stay-green cvs. NPZ-1 and Apex were reciprocally grafted with the N-inefficient and early-senescing cvs. NPZ-2 and Capitol, respectively and grown in hydroponics. The senescence status of older leaves after 12 days of N starvation assessed by SPAD, photosynthesis and the expression of the senescence-specific cysteine protease gene SAG12-1 revealed that the stay-green phenotype of the cvs. NPZ-1 and Apex under N starvation was primarily under the control of leaf-inherent factors. The same four cultivars were submitted to N starvation for up to 12 days in a time-course experiment. The specific leaf contents of biologically active and inactive cytokinins (CKs) and the expression of genes involved in CK homeostasis revealed that under N starvation leaves of early-senescing cultivars were characterized by inactivation of biologically active CKs, whereas in stay-green cultivars synthesis, activation, binding of and response to biologically active CKs were favoured. These results suggest that the homeostasis of biologically active CKs was the predominant leaf-inherent factor for cultivar differences in N starvation-induced leaf senescence and thus N efficiency.
authors.affiliation: Institute of Plant Nutrition, Leibniz University of Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Koeslin-Findeklee
authors.affiliation: Institute of Plant Nutrition, Leibniz University of Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Becker
authors.affiliation: Department of Plant and Environmental Sciences, Copenhagen Plant Science Center, University of Copenhagen, Højbakkegård Allé13, DK-2630 Taastrup, Denmark.
authors.forename: Eric
authors.initials: E
authors.lastname: van der Graaff
authors.affiliation: Department of Plant and Environmental Sciences, Copenhagen Plant Science Center, University of Copenhagen, Højbakkegård Allé13, DK-2630 Taastrup, Denmark Global Change Research Centre, CzechGlobe AS CR, v.v.i., Drásov 470, Cz-664 24 Drásov, Czech Republic.
authors.forename: Thomas
authors.initials: T
authors.lastname: Roitsch
authors.affiliation: Institute of Plant Nutrition, Leibniz University of Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany horst@pflern.uni-hannover.de.
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Horst
mesh_terms: D029688:Brassica napus / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005960:Glucosides / Q000378:metabolism; D006706:Homeostasis; D009584:Nitrogen / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D012621:Seasons; D015398:Signal Transduction / Q000235:genetics; D015026:Zeatin / Q000378:metabolism
chemical_list: D003583:Cytokinins; D005960:Glucosides; D010940:Plant Proteins; C095437:zeatin-O-glucoside; D002734:Chlorophyll; D015026:Zeatin; D010447:Peptide Hydrolases; D009584:Nitrogen
keywords: Brassica napus; cytokinins; genotypic differences; leaf senescence; nitrogen efficiency; nitrogen starvation; reciprocal grafting; stay-green.