Paxillus involutus Strains MAJ and NAU Mediate K+/Na+ Homeostasis in Ectomycorrhizal Populus × canescens under Sodium Chloride Stress      

Abstract

Salt-induced fluxes of H+ , Na + , K + , and Ca 2+ were investigated in ectomycorrhizal (EM) associations formed by Paxillus involutus (strains MAJ and NAU) with the salt-sensitive poplar hybrid Populus 3 canescens. A scanning ion-selective electrode technique was used to measure flux profiles in non-EM roots and axenically grown EM cultures of the two P. involutus isolates to identify whether the major alterations detected in EM roots were promoted by the fungal partner. EM plants exhibited a more pronounced ability to maintain K + /Na + homeostasis under salt stress. The influx of Na + was reduced after short-term (50 mM NaCl, 24 h) and long-term (50 mM NaCl, 7 d) exposure to salt stress in mycorrhizal roots, especially in NAU associations. Flux data for P. involutus and susceptibility to Na + -transport inhibitors indicated that fungal colonization contributed to active Na + extrusion and H + uptake in the salinized roots of P. 3 canescens. Moreover, EM plants retained the ability to reduce the salt-induced K + efflux, especially under long-term salinity. Our study suggests that P. involutus assists in maintaining K + homeostasis by delivering this nutrient to host plants and slowing the loss of K + under salt stress. EM P. 3 canescens plants exhibited an enhanced Ca 2+ uptake ability, whereas short-term and long-term treatments caused a marked Ca 2+ efflux from mycorrhizal roots, especially from NAU-colonized roots. We suggest that the release of additional Ca 2+ mediated K + /Na + homeostasis in EM plants under salt stress.

Influence of mycorrhizal inoculation on growth of micropropagated Populus × canescens lines in metal-contaminated soils

“…To date, few studies have reported on the effects of mycorrhizal fungi on the acclimatization of microplants of forest trees to ex vitro conditions. A positive effect of in vitro ECM inoculation on poplar growth was previously reported for Populus tremula L. 9 Populus tremuloides Mich (Hampp et al 1996;Loewe et al 2000) and for P. 9 canescens (Gafur et al 2004;Li et al 2012;Ma et al 2014). Inoculation of microplants ex vitro with mycorrhizal fungi has been shown to improve poplar survival rate, health status, and growth post-acclimatization (Langer et al 2008).…”

“…Under natural conditions, H. crustuliniforme and P. involutus develop ECM symbiosis with a wide Laccaria laccata, and Pisolithus tinctorius) did not form ECM structures with P. deltoides roots, although they colonized extensively the growth medium (Reddy and Satyanarayana 1998). Selected strains of P. involutus used for inoculation of P. 9 canescens microplants enhanced tolerance of the poplar plants to salt stress (Langenfeld-Heyser et al 2007;Li et al 2012), drought stress (Luo et al 2009b), and cadmium toxicity (Ma et al 2014). Although Populus spp.…”

“…ECM symbionts can influence physiological and molecular processes of the poplar and modify mechanism of heavy metal detoxification . No data were reported yet on a contribution of AM fungi in colonization of P. 9 canescens roots, but in several studies of P. 9 canescens microplants or cuttings have been colonized effectively with ECM fungi (Gafur et al 2004;Langenfeld-Heyser et al 2007;Luo et al 2009b;Li et al 2012;Ma et al 2014). Species and strains of mycorrhizal fungi vary in their ability to develop mycorrhizal symbiosis with tree microplants (Gafur et al 2004;Luo et al 2009a, b), in their tolerance to toxic metals (Blaudez et al 2000;Ma et al 2014;Luo et al 2014), and in their capacity for metal accumulation and detoxification (Rudawska and Leski 2005;Baldrian 2009;Luo et al 2011).…”

“…Species and strains of mycorrhizal fungi vary in their ability to develop mycorrhizal symbiosis with tree microplants (Gafur et al 2004;Luo et al 2009a, b), in their tolerance to toxic metals (Blaudez et al 2000;Ma et al 2014;Luo et al 2014), and in their capacity for metal accumulation and detoxification (Rudawska and Leski 2005;Baldrian 2009;Luo et al 2011). Choosing compatible and efficient mycorrhizal symbionts (species/isolates) is required to ameliorate successfully the negative impacts of toxic contaminants on plants (Gafur et al 2004;Timonen et al 2008;Li et al 2012;Polle et al 2013;Ma et al 2014).…”

Physiological Responses of Alfalfa to High-level Salt Stress: Root Ion Flux and Stomatal Characteristics

“…Instead, a non-invasive micro-test technique (NMT) successfully developed by Shabala and coadjutant colleagues Garnett et al, 2001) is widely accepted due to its precise detections on the movement of plasma membrane (PM) H + -ATPase in the Na + /H + antiport according to ion kinetics in response to salt shock. Under salt stress, the pattern of short-term flux profiles of salinity ions of Na + , K + , and Cl -, has been well quantified using NMT on Arabidopsis (Shabala et al, 2005), Poplar (Sun et al, 2009), Mangrove (Lu et al, 2013), and some strains in mycorrhizal Poplar roots (Li et al, 2012;Ma et al, 2014). According to these studies, the short-term salt-induced efflux of intracellular K + was highlighted because salt impact would be intensified when K + loss is accompanied by accumulation of Na + inside the cytosol with a high level of Na + concentration in the range of 50-200 mM (Maathuis and Amtmann, 1999;Flowers and Hajibagheri, 2001;Britto et al, 2010).…”