AUTHOR=Zhang Yuhong , Sa Gang , Zhang Yinan , Zhu Zhimei , Deng Shurong , Sun Jian , Li Nianfei , Li Jing , Yao Jun , Zhao Nan , Zhao Rui , Ma Xujun , Polle Andrea , Chen Shaoliang TITLE=Paxillus involutus-Facilitated Cd2+ Influx through Plasma Membrane Ca2+-Permeable Channels Is Stimulated by H2O2 and H+-ATPase in Ectomycorrhizal Populus × canescens under Cadmium Stress JOURNAL=Frontiers in Plant Science VOLUME=7 YEAR=2017 URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.01975 DOI=10.3389/fpls.2016.01975 ISSN=1664-462X ABSTRACT=

Using a Non-invasive Micro-test Technique, flux profiles of Cd²⁺, Ca²⁺, and H⁺ were investigated in axenically grown cultures of two strains of Paxillus involutus (MAJ and NAU), ectomycorrhizae formed by these fungi with the woody Cd²⁺-hyperaccumulator, Populus × canescens, and non-mycorrhizal (NM) roots. The influx of Cd²⁺ increased in fungal mycelia, NM and ectomycorrhizal (EM) roots upon a 40-min shock, after short-term (ST, 24 h), or long-term (LT, 7 days) exposure to a hydroponic environment of 50 μM CdCl₂. Cd²⁺ treatments (shock, ST, and LT) decreased Ca²⁺ influx in NM and EM roots but led to an enhanced influx of Ca²⁺ in axenically grown EM cultures of the two P. involutus isolates. The susceptibility of Cd²⁺ flux to typical Ca²⁺ channel blockers (LaCl₃, GdCl₃, verapamil, and TEA) in fungal mycelia and poplar roots indicated that the Cd²⁺ entry occurred mainly through Ca²⁺-permeable channels in the plasma membrane (PM). Cd²⁺ treatment resulted in H₂O₂ production. H₂O₂ exposure accelerated the entry of Cd²⁺ and Ca²⁺ in NM and EM roots. Cd²⁺ further stimulated H⁺ pumping activity benefiting NM and EM roots to maintain an acidic environment, which favored the entry of Cd²⁺ across the PM. A scavenger of reactive oxygen species, DMTU, and an inhibitor of PM H⁺-ATPase, orthovanadate, decreased Ca²⁺ and Cd²⁺ influx in NM and EM roots, suggesting that the entry of Cd²⁺ through Ca²⁺-permeable channels is stimulated by H₂O₂ and H⁺ pumps. Compared to NM roots, EM roots exhibited higher Cd²⁺-fluxes under shock, ST, and LT Cd²⁺ treatments. We conclude that ectomycorrhizal P. × canescens roots retained a pronounced H₂O₂ production and a high H⁺-pumping activity, which activated PM Ca²⁺ channels and thus facilitated a high influx of Cd²⁺ under Cd²⁺ stress.