Ectomycorrhizas with Paxillus involutus enhance cadmium uptake and tolerance in Populus x canescens

Ectomycorrhizas (EMs), which are symbiotic organs formed between tree roots and certain fungi, can mediate cadmium (Cd) tolerance of host plants, but the underlying physiological and molecular mechanisms are not fully understood. To investigate EMs mediated Cd tolerance in woody plants, Populusxcanescens was inoculated with Paxillus involutus (strain MAJ) to establish mycorrhizal roots. Mycorrhizal poplars and non-mycorrhizal controls were exposed to 0 or 50M CdSO4. EMs displayed higher net Cd2+ influx than non-mycorrhizal roots. Net Cd2+ influx was coupled with net H+ efflux and inactivation of plasma membrane (PM) H+-ATPases reduced Cd2+ uptake of EMs less than of non-mycorrhizal roots. Consistent with higher Cd2+ uptake in EMs, in most cases, transcript levels of genes involved in Cd2+ uptake, transport and detoxification processes were increased in EMs compared to non-mycorrhizal roots. Higher CO2 assimilation, improved nutrient and carbohydrate status, and alleviated oxidative stress were found in mycorrhizal compared to non-mycorrhizal poplars despite higher Cd2+ accumulation. These results indicate that mycorrhizas increase Cd2+ uptake, probably by an enlarged root volume and overexpression of genes involved in Cd2+ uptake and transport, and concurrently enhance Po.xcanescensCd tolerance by increased detoxification, improved nutrient and carbohydrate status and defence preparedness.