title: Redox markers for drought-induced nodule senescence, a process occurring after drought-induced senescence of the lowest leaves in soybean (Glycine max).
abstract: OBJECTIVE
  Water is an increasingly scarce resource that limits crop productivity in many parts of the world, and the frequency and severity of drought are predicted to increase as a result of climate change. Improving tolerance to drought stress is therefore important for maximizing future crop yields. The aim of this study was to compare the effects of drought on soybean (Glycine max) leaves and nodules in order to define phenotypic markers and changes in cellular redox state that characterize the stress response in different organs, and to characterize the relationships between leaf and nodule senescence during drought.
  
  
  METHODS
  Leaf and crown nodule metabolite pools were measured together with leaf and soil water contents, and leaf chlorophyll, total protein contents and chlorophyll a fluorescence quenching parameters in nodulated soybeans that were grown under either well-watered conditions or deprived of water for up to 21 d.
  
  
  RESULTS
  Ureides, ascorbate, protein, chlorophyll and the ratios of variable chlorophyll a fluorescence (Fv') to maximal chlorophyll a fluorescence (Fm') fell to levels below detection in the oldest leaves after 21 d of drought. While these drought-induced responses were not observed in the youngest leaf ranks, the Fv'/Fm' ratios, pyridine nucleotide levels and the reduction state of the ascorbate pool were lower in all leaf ranks after 21 d of drought. In contrast to leaves, total nodule protein, pyridine nucleotides, ureides, ascorbate and glutathione contents increased as a result of the drought treatment. However, the nodule ascorbate pool was significantly less reduced as a result of drought. Higher levels of transcripts encoding two peroxiredoxins were detected in nodules exposed to drought stress but senescence-associated transcripts and other mRNAs encoding redox-related proteins were similar under both conditions.
  
  
  CONCLUSIONS
  While the physiological impact of the drought was perceived throughout the shoot, stress-induced senescence occurred only in the oldest leaf ranks. At this stage, a number of drought-induced changes in nodule metabolites were observed but no metabolite or transcript markers of senescence could be detected. It is concluded that stress-induced senescence in the lowest leaf ranks precedes nodule senescence, suggesting that leaves of low photosynthetic capacity are sacrificed in favour of nodule nitrogen metabolism.
authors: Centre for Plant Sciences, Faculty of Biology, University of Leeds, Leeds LS2 9JT, UK and.
authors: Belén
authors: B
authors: Marquez-Garcia
authors: Centre for Plant Sciences, Faculty of Biology, University of Leeds, Leeds LS2 9JT, UK and.
authors: Daniel
authors: D
authors: Shaw
authors: Centre for Plant Sciences, Faculty of Biology, University of Leeds, Leeds LS2 9JT, UK and.
authors: James William
authors: JW
authors: Cooper
authors: Centre for Plant Sciences, Faculty of Biology, University of Leeds, Leeds LS2 9JT, UK and.
authors: Barbara
authors: B
authors: Karpinska
authors: Centre for Plant Sciences, Faculty of Biology, University of Leeds, Leeds LS2 9JT, UK and.
authors: Marian Dorcas
authors: MD
authors: Quain
authors: Centre for Plant Sciences, Faculty of Biology, University of Leeds, Leeds LS2 9JT, UK and Forestry and Agricultural Biotechnology Institute, Plant Science Department, University of Pretoria, Pretoria 0002, South Africa.
authors: Eugene Matome
authors: EM
authors: Makgopa
authors: Centre for Plant Sciences, Faculty of Biology, University of Leeds, Leeds LS2 9JT, UK and Forestry and Agricultural Biotechnology Institute, Plant Science Department, University of Pretoria, Pretoria 0002, South Africa.
authors: Karl
authors: K
authors: Kunert
authors: Centre for Plant Sciences, Faculty of Biology, University of Leeds, Leeds LS2 9JT, UK and C.Foyer@leeds.ac.uk.
authors: Christine Helen
authors: CH
authors: Foyer
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D057231:Climate Change; D055864:Droughts; D010084:Oxidation-Reduction; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology; D013025:Glycine max / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D013312:Stress, Physiological
chemical_list: D015415:Biomarkers
keywords: Ascorbic acid; Glycine max; ROS; cysteine proteases; drought; nodules; peroxiredoxin; reactive oxygen species; redox regulation; senescence; soybean; ureides; water stress