Abstract
Cadmium (Cd2+) pollution occurring in salt-affected soils has become an increasing environmental concern in the world. Fast-growing poplars have been widely utilized for phytoremediation of soil contaminating heavy metals (HMs). However, the woody Cd2+-hyperaccumulator, Populus × canescens, is relatively salt-sensitive and therefore cannot be directly used to remediate HMs from salt-affected soils. The aim of the present study was to testify whether colonization of P. × canescens with ectomycorrhizal (EM) fungi, a strategy known to enhance salt tolerance, provides an opportunity for affordable remediation of Cd2+-polluted saline soils. Ectomycorrhization with Paxillus involutus strains facilitated Cd2+ enrichment in P. × canescens upon CdCl2 exposures (50 μM, 30 min to 24 h). The fungus-stimulated Cd2+ in roots was significantly restricted by inhibitors of plasmalemma H+-ATPases and Ca2+-permeable channels (CaPCs), but stimulated by an activator of plasmalemma H+-ATPases. NaCl (100 mM) lowered the transient and steady-state Cd2+ influx in roots and fungal mycelia. Noteworthy, P. involutus colonization partly reverted the salt suppression of Cd2+ uptake in poplar roots. EM fungus colonization upregulated transcription of plasmalemma H+-ATPases (PcHA4, 8, 11) and annexins (PcANN1, 2, 4), which might mediate Cd2+ conductance through CaPCs. EM roots retained relatively highly expressed PcHAs and PcANNs, thus facilitating Cd2+ enrichment under co-occurring stress of cadmium and salinity. We conclude that ectomycorrhization of woody hyperaccumulator species such as poplar could improve phytoremediation of Cd2+ in salt-affected areas.
Highlights
Cadmium (Cd2+ ) pollution presents a critical threat to ecological environment and human life [1,2,3,4,5]
We studied Cd2+ uptake in the presence and absence of NaCl and analyzed gene expression of annexins because previous studies show that PeANN1 facilitates Cd2+ enrichment through Ca2+-permeable channels (CaPCs) [79]
We have shown that P. euphratica PeANN1 facilitates cadmium enrichment by regulation of calcium-permeable channels [79]
Summary
Cadmium (Cd2+ ) pollution presents a critical threat to ecological environment and human life [1,2,3,4,5]. The Cd2+ contamination occurring in salt-affected soils has become an increasing environmental concern in recent years [6,7,8,9,10,11,12,13,14,15,16,17]. In some coastal saline zones, soil heavy metal pollution comes from sludge and sewage irrigation [19]. The Cd2+ contamination in salt-affected soils complicates remediation processes [6,7]. Poplar trees have been widely utilized for phytoremediation of soils and water resources contaminated with HMs, because of their fast-growth, large biomass and remarkable Cd2+ accumulation in shoots and below-ground [25,26,27,28,29,30,31]. Several poplars, e.g., Populus tremula, P. × canescens, are known Cd2+ hyperaccumulators [32,33]
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