title: Leaf ion homeostasis and plasma membrane H(+)-ATPase activity in Vicia faba change after extra calcium and potassium supply under salinity.
abstract: Salt stress in plants impacts apoplastic ion activities and cytosolic ionic homeostasis. The ameliorating effects exerted by calcium or potassium on compartmentation of ions in leaves under salinity are not fully understood. To clarify how calcium or potassium supply could ameliorate ion homeostasis and ATPase activities under salinity, 5 mM CaSO4 or 10 mM K2SO4 were added with, or without, 100 mM NaCl for 7 d and 21 d to Vicia faba grown in hydroponics. The apoplastic pH was detected with Oregon Green dextran dye in intact second-uppermost leaves by microscopy-based ratio imaging. The cytosolic Ca(2+), Na(+), K(+) activities and pH were detected in protoplasts loaded with the acetoxy methyl-esters of Fura-2, SBFI, PBFI and BCECF, respectively, using epi-fluorescence microscopy. Furthermore, total Ca(2+), Na(+), K(+) concentrations and growth parameters were investigated. The ATPase hydrolyzing activity increased with time, but decreased after long salinity treatment. The activity largely increased in calcium-treated plants, but was depressed in potassium-treated plants after 7 d. The calcium supply increased Vmax, and the ATPase activity increased with salinity in a non-competitive way for 7 d and 21 d. The potassium supply instead decreased activity competitively with Na(+), after 21 d of salinity, with different effects on Km and Vmax. The confirmed higher ATPase activity was related with apoplast acidification, cytosol alkalinization and low cytosolic [Na(+)], and thus, might be an explanation why extra calcium improved shoot and leaf growth.
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden; Institute of Plant Nutrition and Soil Science, Kiel University, Hermann Rodewald Strasse 2, D-24118 Kiel, Germany; Plant Physiology Section, Plant Botany Department, Faculty of Agriculture, Cairo University, 12613 Giza, Egypt. Electronic address: morgan@plantnutrition.uni-kiel.de.
authors.forename: Sherif H
authors.initials: SH
authors.lastname: Morgan
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden. Electronic address: pooja.jha.maity@su.se.
authors.forename: Pooja Jha
authors.initials: PJ
authors.lastname: Maity
authors.affiliation: Institute of Plant Nutrition and Soil Science, Kiel University, Hermann Rodewald Strasse 2, D-24118 Kiel, Germany. Electronic address: cmgeilfus@plantnutrition.uni-kiel.de.
authors.forename: Christoph-Martin
authors.initials: CM
authors.lastname: Geilfus
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden. Electronic address: sylvia.lindberg@su.se.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Lindberg
authors.affiliation: Institute of Plant Nutrition and Soil Science, Kiel University, Hermann Rodewald Strasse 2, D-24118 Kiel, Germany. Electronic address: khmuehling@plantnutrition.uni-kiel.de.
authors.forename: Karl Hermann
authors.initials: KH
authors.lastname: Mühling
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology*; D006706:Homeostasis; D007477:Ions / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology* / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D054712:Salinity; D031307:Vicia faba / Q000201:enzymology*
chemical_list: D007477:Ions; D006180:Proton-Translocating ATPases; D011188:Potassium; D002118:Calcium
keywords: Apoplastic pH; Calcium and potassium supply; Cytosolic free ions; Plasma membrane H(+)-ATPase; Salinity