title: Quantitative limitations to photosynthesis in K deficient sunflower and their implications on water-use efficiency.
abstract: Potassium (K) is crucial for crop growth and is strongly related to stress tolerance and water-use efficiency (WUE). A major physiological effect of K deficiency is the inhibition of net CO2assimilation (AN) during photosynthesis. Whether this reduction originates from limitations either to photochemical energy conversion or biochemical CO2fixation or from a limitation to CO2diffusion through stomata and the leaf mesophyll is debated. In this study, limitations to photosynthetic carbon gain of sunflower (Helianthus annuus L.) under K deficiency and PEG- induced water deficit were quantified and their implications on plant- and leaf-scale WUE (WUEP, WUEL) were evaluated. Results show that neither maximum quantum use efficiency (Fv/Fm) nor in-vivo RubisCo activity were directly affected by K deficiency and that the observed impairment of ANwas primarily due to decreased CO2mesophyll conductance (gm). K deficiency additionally impaired leaf area development which, together with reduced AN, resulted in inhibition of plant growth and a reduction of WUEP. Contrastingly, WUELwas not affected by K supply which indicated no inhibition of stomatal control. PEG-stress further impeded ANby stomatal closure and resulted in enhanced WUELand high oxidative stress. It can be concluded from this study that reduction of gmis a major response of leaves to K deficiency, possibly due to changes in leaf anatomy, which negatively affects ANand contributes to the typical symptoms like oxidative stress, growth inhibition and reduced WUEP.
authors.affiliation: Institute of Applied Plant Nutrition, University of Göttingen, Carl-Sprengel-Weg 1, 37075 Göttingen, Germany. Electronic address: balint.jakli@yahoo.com.
authors.forename: Bálint
authors.initials: B
authors.lastname: Jákli
authors.affiliation: Institute of Applied Plant Nutrition, University of Göttingen, Carl-Sprengel-Weg 1, 37075 Göttingen, Germany.
authors.forename: Ershad
authors.initials: E
authors.lastname: Tavakol
authors.affiliation: Institute of Applied Plant Nutrition, University of Göttingen, Carl-Sprengel-Weg 1, 37075 Göttingen, Germany.
authors.forename: Merle
authors.initials: M
authors.lastname: Tränkner
authors.affiliation: Institute of Applied Plant Nutrition, University of Göttingen, Carl-Sprengel-Weg 1, 37075 Göttingen, Germany.
authors.forename: Mehmet
authors.initials: M
authors.lastname: Senbayram
authors.affiliation: Institute of Applied Plant Nutrition, University of Göttingen, Carl-Sprengel-Weg 1, 37075 Göttingen, Germany; Department of Crop Science, Section of Plant Nutrition & Crop Physiology, University of Göttingen, Carl-Sprengel-Weg 1, 37075 Göttingen, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Dittert
mesh_terms: D018533:Biomass; D002734:Chlorophyll / Q000378:metabolism; D005453:Fluorescence; D005740:Gases / Q000378:metabolism; D006368:Helianthus / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D006861:Hydrogen Peroxide / Q000378:metabolism; D058503:Mesophyll Cells / Q000187:drug effects / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000494:pharmacology*; D013997:Time Factors; D014867:Water / Q000378:metabolism*
chemical_list: D005740:Gases; D045332:Photosystem II Protein Complex; D014867:Water; D002734:Chlorophyll; D006861:Hydrogen Peroxide; D011188:Potassium
keywords: Chlorophyll fluorescence; Leaf gas exchange; Mesophyll conductance; Photosynthesis; Potassium nutrition; Water use efficiency