title: Senescence-induced ectopic expression of the A. tumefaciens ipt gene in wheat delays leaf senescence, increases cytokinin content, nitrate influx, and nitrate reductase activity, but does not affect grain yield.
abstract: The manipulation of cytokinin levels by senescence-regulated expression of the Agrobacterium tumefaciens ipt gene through its control by the Arabidopsis SAG12 (senescence-associated gene 12) promoter is an efficient tool for the prolongation of leaf photosynthetic activity which potentially can affect plant productivity. In the present study, the efficiency of this approach was tested on wheat (Triticum aestivum L.)-a monocarpic plant characterized by a fast switch from vegetative to reproductive growth, and rapid translocation of metabolites from leaves to developing grains after anthesis. When compared with the wild-type (WT) control plants, the SAG12::ipt wheat plants exhibited delayed chlorophyll degradation only when grown under limited nitrogen (N) supply. Ten days after anthesis the content of chlorophyll and bioactive cytokinins of the first (flag) leaf of the transgenic plants was 32% and 65% higher, respectively, than that of the control. There was a progressive increase in nitrate influx and nitrate reductase activity. However, the SAG12::ipt and the WT plants did not show differences in yield-related parameters including number of grains and grain weight. These results suggest that the delay of leaf senescence in wheat also delays the translocation of metabolites from leaves to developing grains, as indicated by higher accumulation of ((15)N-labelled) N in spikes of control compared with transgenic plants prior to anthesis. This delay interferes with the wheat reproductive strategy that is based on a fast programmed translocation of metabolites from the senescing leaves to the reproductive sinks shortly after anthesis.
authors.affiliation: Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Rozvojová 263, 16502 Prague 6, Czech Republic.
authors.forename: Blanka
authors.initials: B
authors.lastname: Sykorová
authors.forename: Gabriela
authors.initials: G
authors.lastname: Kuresová
authors.forename: Sasha
authors.initials: S
authors.lastname: Daskalova
authors.forename: Marie
authors.initials: M
authors.lastname: Trcková
authors.forename: Klára
authors.initials: K
authors.lastname: Hoyerová
authors.forename: Ivana
authors.initials: I
authors.lastname: Raimanová
authors.forename: Václav
authors.initials: V
authors.lastname: Motyka
authors.forename: Alena
authors.initials: A
authors.lastname: Trávnícková
authors.forename: Malcolm C
authors.initials: MC
authors.lastname: Elliott
authors.forename: Miroslav
authors.initials: M
authors.lastname: Kamínek
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics; D018533:Biomass; D002734:Chlorophyll / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000235:genetics; D003583:Cytokinins / Q000378:metabolism*; D050901:Nitrate Reductase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D009587:Nitrogen Isotopes / Q000378:metabolism; D010641:Phenotype; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology*; D030821:Plants, Genetically Modified / Q000378:metabolism / Q000502:physiology; D011401:Promoter Regions, Genetic; D012098:Reproduction / Q000502:physiology; D012639:Seeds / Q000254:growth & development* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014908:Triticum / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D009566:Nitrates; D009587:Nitrogen Isotopes; D002734:Chlorophyll; D050901:Nitrate Reductase; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase; C402082:SAG12 protein, Arabidopsis; D003546:Cysteine Endopeptidases