Amelioration of nitrate uptake under salt stress by ectomycorrhiza with and without a Hartig net

Abstract

Summary Salt stress is an important environmental cue impeding poplar nitrogen nutrition. Here, we characterized the impact of salinity on proton‐driven nitrate fluxes in ectomycorrhizal roots and the importance of a Hartig net for nitrate uptake. We employed two Paxillus involutus strains for root colonization: MAJ , which forms typical ectomycorrhizal structures (mantle and Hartig net), and NAU , colonizing roots with a thin, loose hyphal sheath. Fungus‐colonized and noncolonized Populus × canescens were exposed to sodium chloride and used to measure root surface pH , nitrate ( NO 3 − ) flux and transcription of NO 3 − transporters (NRTs; Pc NRT 1.1 , ‐ 1.2 , ‐ 2.1 ), and plasmalemma proton ATPases (HAs; Pc HA 4 , ‐ 8 , ‐11 ). Paxillus colonization enhanced root NO 3 − uptake, decreased surface pH , and stimulated NRT s and HA 4 of the host regardless the presence or absence of a Hartig net. Under salt stress, noncolonized roots exhibited strong net NO 3 − efflux, whereas beneficial effects of fungal colonization on surface pH and HA s prevented NO 3 − loss. Inhibition of HA s abolished NO 3 − influx under all conditions. We found that stimulation of HA s was crucial for the beneficial influence of ectomycorrhiza on NO 3 − uptake, whereas the presence of a Hartig net was not required for improved NO 3 − translocation. Mycorrhizas may contribute to host adaptation to salt‐affected environments by keeping up NO 3 − nutrition.

Ectomycorrhizal and Dark Septate Fungal Associations of Pinyon Pine Are Differentially Affected by Experimental Drought and Warming

“…They were observed in only one treatment each where they made up less than 2% of the community, but they were included in subsequent statistical analyses despite the poorly formed Hartig net. Recent research indicates that EM fungi can still carry out critical functions even without a functional Hartig net (Sa et al, 2019). Members of the Heliotiales can form associations with ectomycorrhizas (Nakamura et al, 2018) and it is possible that this is what we observed.…”

Potential Mechanisms of Abiotic Stress Tolerance in Crop Plants Induced by Thiourea

“…Similarly, foliar application of TU improved the grain yield of salt-stressed wheat and its protein concentration more than soil-applied bagasse ash (Seleiman and Kheir, 2018), mainly due to greater N uptake (Garg et al, 2006). Excess salinity causes excessive absorption of individual ions leading to toxicity and retards absorption of other essential plant nutrients leading to nutrient deficiencies (Sa et al, 2019). However, TU improves the mechanisms underlying salt-tolerance by modulating the K+/Na+ ratio and increasing uptake of K + , Ca 2+ , and N in maize plants (Kaya et al, 2016).…”

Integrated proteomic and metabolomic analyses revealed molecular adjustments in Populus × canescens colonized with the ectomycorrhizal fungus Paxillus involutus, which limited plant host growth

“…We utilized the in vitro Populus × canescens–P. involutus system – one of the most frequently used systems for analyses of ectomycorrhizal symbiosis in poplar (Gafur et al ., 2004, 2007; Müller et al ., 2013; Szuba, 2015; Sa et al ., 2019). Populus × canescens microcuttings were propagated in modified Murashige and Skoog (MS) agar media consisting of 1.5% sucrose as described previously (Szuba et al ., 2017).…”

“…Resource exchange occurs through cell walls (CWs; Balestrini and Bonfante, 2014) mainly via a network of fungal cells present between epidermal and cortical plant cells called the Hartig net (HN) (Smith and Read, 2008). The key role of the HN in N uptake was recently challenged (Sa et al ., 2019), although it is still considered an important surface for resource exchange between symbiotic partners (Smith and Read, 2008; Tschaplenski et al ., 2014). Of similar importance in facilitating resource exchange may be the loosening and changes in the structure of host CWs (Nehls, 2008; Balestrini and Bonfante, 2014; Veneault‐Fourrey et al ., 2014).…”