Research article Leaf ion homeostasis and plasma membrane H þ -ATPase activity in Vicia faba change after extra calcium and potassium supply under salinity Sherif H. Morgan a, b, c , Pooja Jha Maity a , Christoph-Martin Geilfus b , Sylvia Lindberg a, * , Karl Hermann Mühling b a Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden b Institute of Plant Nutrition and Soil Science, Kiel University, Hermann Rodewald Strasse 2, D-24118 Kiel, Germany c Plant Physiology Section, Plant Botany Department, Faculty of Agriculture, Cairo University, 12613 Giza, Egypt article info Article history: Received 20 November 2013 Accepted 17 June 2014 Available online 25 June 2014 Keywords: Apoplastic pH Calcium and potassium supply Cytosolic free ions Plasma membrane H þ -ATPase 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 CaSO 4 or 10 mM K 2 SO 4 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 2þ , Na þ ,K þ 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 2þ , Na þ ,K þ 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 þ , 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 þ ], and thus, might be an explanation why extra calcium improved shoot and leaf growth. © 2014 Published by Elsevier Masson SAS. 1. Introduction One strategy to reduce the adverse effects of salinity is to add nutrients such as calcium or potassium in order to ameliorate the nutritional deficiencies that usually occur under salinity (Shabala, 2002; Shabala et al., 2006; Sun et al., 2010). An adequate level of calcium and potassium in growing leaf cells can be beneficial for improving plant growth under salinity (Shabala et al., 2006; Munns and Tester, 2008). In that context, it can be suggested that salinity may disturb the essential Ca 2þ functions without disturbing the overall tissue concentrations of Ca 2þ , as the cytosolic Ca 2þ activity, [Ca 2þ ] cyt , is in nM range, whereas the overall tissue concentrations are in mM range (Felle, 1988; Plieth, 2001). Moreover, Na þ com- petes with K þ for intracellular influx, as these cations can be transported by the same proteins (reviewed by Demidchik and Maathuis, 2007; Flowers et al., 2010; and recently by Shabala, 2013). Abbreviation: BCECF,AM, acetoxy methyl ester of 2', 7'-bis-(carboxy ethyl)-5-, (and 6)-carboxy fluorescein; [Ca 2þ ] cyt , cytosolic free Ca 2þ concentration; Fura- 2,AM, acetoxy methyl ester of calcium binding benzofuran; [K þ ] cyt , cytosolic free K þ concentration; Km, apparent enzyme-substrate affinity constant; [Na þ ] cyt , cytosolic free Na 2þ concentration; PBFI,AM, acetoxy methyl ester of potassium-binding benzofuran; SBFI,AM, acetoxy methyl ester of sodium-binding benzofuran; pH apo , apoplastic pH; pH cyt , cytoplasmic pH; PM, plasma membrane; ST, short term of growth (7 d); LT, long term of growth (21 d); Vmax, reaction rate at saturating concentration of substrate. * Corresponding author. Tel.: þ46 8 161213; fax: þ46 8 165525. E-mail addresses: morgan@plantnutrition.uni-kiel.de, morgan@agr.cu.edu.eg (S.H. Morgan), pooja.jha.maity@su.se (P.J. Maity), cmgeilfus@plantnutrition.uni- kiel.de (C.-M. Geilfus), sylvia.lindberg@su.se, sylvia.lindberg@botan.su.se (S. Lindberg), khmuehling@plantnutrition.uni-kiel.de (K.H. Mühling). Contents lists available at ScienceDirect Plant Physiology and Biochemistry journal homepage: www.elsevier.com/locate/plaphy http://dx.doi.org/10.1016/j.plaphy.2014.06.010 0981-9428/© 2014 Published by Elsevier Masson SAS. Plant Physiology and Biochemistry 82 (2014) 244e253