Environmental and Experimental Botany 87 (2013) 69–78 Contents lists available at SciVerse ScienceDirect Environmental and Experimental Botany journa l h omepa g e: www.elsevier.com/locate/envexpbot Differential tolerance to combined salinity and O 2 deficiency in the halophytic grasses Puccinellia ciliata and Thinopyrum ponticum: The importance of K + retention in roots N.L. Teakle a,b,1 , N. Bazihizina a,b , S. Shabala c , T.D. Colmer b,d,∗ , E.G. Barrett-Lennard a,b,e , A. Rodrigo-Moreno c,g , A.E. Läuchli b,f a State Centre of Excellence for Ecohydrology, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia b School of Plant Biology, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6019, Australia c School of Agricultural Sciences and Tasmanian Institute of Agricultural Research, Private Bag 54, University of Tasmania, Hobart TAS 7001, Australia d The UWA Institute of Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia e Department of Agriculture and Food Western Australia, 3 Baron-Hay Court, South Perth, WA 6151, Australia f Department of Land, Air and Water Resources, University of California, 1 Shields Ave, Davis CA 95616-8627, USA g Universitat Autònoma de Barcelona, Facultat de Biociències. Edifici C, 08193 Bellaterra, Barcelona, Spain a r t i c l e i n f o Article history: Received 21 June 2012 Received in revised form 21 August 2012 Accepted 19 September 2012 Keywords: Adventitious roots Halophytes Membrane potential Potassium Sodium, Waterlogging a b s t r a c t Saline environments of terrestrial halophytes are often prone to waterlogging, yet the effects on halo- phytes of combined salinity and waterlogging have rarely been studied. Either salinity or hypoxia (low O 2 ) alone can interfere with K + homeostasis, therefore the combination of salinity or hypoxia is expected to impact significantly on K + retention in roots. We studied mechanisms of tolerance to the interaction of salinity with hypoxia in Puccinellia ciliata and Thinopyrum ponticum, halophytic grasses that differ in waterlogging tolerance. Plants were exposed to aerated and stagnant saline (250 mM NaCl) treatments with low (0.25 mM) and high (4 mM) K + levels; growth, net ion fluxes and tissue ion concentrations were determined. P. ciliata was more tolerant than T. ponticum to stagnant-saline treatment, producing twice the biomass of adventitious roots, which accumulated high levels of Na + , and had lower shoot Na + . After 24 h of saline hypoxic treatment, MIFE measurements revealed a net uptake of K + (∼40 nmol m -2 s -1 ) for P. ciliata, but a net loss of K + (∼20 nmol m -2 s -1 ) for the more waterlogging sensitive T. ponticum. NaCl alone induced K + efflux from roots of both species, with channel blocker tests implicating GORK-like channels. P. ciliata had constitutively a more negative root cell membrane potential than T. ponticum (-150 versus -115 mV). Tolerance to salinity and hypoxia in P. ciliata is related to increased production of adventitious roots, regulation of shoot K + /Na + , and a superior ability to maintain negative membrane potential in root cells, resulting in greater retention of K + . © 2012 Elsevier B.V. All rights reserved. 1. Introduction Salinity is an environmental constraint that affects plant growth and development in a range of landscapes, for both irrigated and non-irrigated agricultural land (Ghassemi et al., 1995). Species ∗ Corresponding author at: School of Plant Biology (M084), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. Tel.: +61 8 6488 1993; fax: +61 8 6488 1108. E-mail addresses: n.ayers@ecu.edu.au (N.L. Teakle), nadia.bazihizina@uwa.edu.au (N. Bazihizina), Sergey.Shabala@utas.edu.au (S. Shabala), timothy.colmer@uwa.edu.au (T.D. Colmer), ed.barrett-lennard@agric.wa.gov.au (E.G. Barrett-Lennard), Ana.Rodrigo@uab.cat (A. Rodrigo-Moreno), aelauchli@ucdavis.edu (A.E. Läuchli). 1 Present address: Natasha Ayers, Graduate Research School, Edith Cowan Uni- versity, 270 Joondalup Dr, Joondalup, WA 6027, Australia. that thrive in these environments and are adapted to salinity are called halophytes. The physiology of halophytes has been studied extensively, and their salinity tolerance is primarily gov- erned by controlled uptake and compartmentalization of Na + , K + , and Cl - (Flowers and Colmer, 2008; Shabala and Mackay, 2011). Many of the habitats occupied by terrestrial halophytes are not only saline, but also prone to waterlogging (Colmer and Flowers, 2008). Waterlogging causes soils to become hypoxic, due to biological consumption of O 2 without its effective replacement (Ponnamperuma, 1984). While the growth effects of combined salinity and waterlogging have been studied for some halophytes (see Colmer and Flowers, 2008), the mechanisms of tolerance are poorly understood. Furthermore, the adverse interactive effects of these stresses must be considered in the design of revegetation pro- grammes for salt-affected lands (Barrett-Lennard, 2003; Bennett et al., 2009). 0098-8472/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.envexpbot.2012.09.006