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.

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.

Amifostine has been the only small molecule radio-protector approved by FDA for decades; however, the serious adverse effects limit its clinical use. To address the toxicity issues and maintain the good potency, a series of modified small polycysteine peptides had been prepared. Among them, compound 5 exhibited the highest radio-protective efficacy, the same as amifostine, but much better safety profile. To confirm the correlation between the radiation-protective efficacy and the DNA binding capability, each of the enantiomers of the polycysteine peptides had been prepared. As a result, the l-configuration compounds had obviously higher efficacy than the corresponding d-configuration enantiomers; among them, compound 5 showed the highest DNA binding capability and radiation-protective efficacy. To our knowledge, this is the first study that has proved their correlations using direct comparison. Further exploration of the mechanism revealed that the ionizing radiation (IR) triggered ferroptosis inhibition by compound 5 could be one of the pathways for the protection effect, which was different from amifostine. In summary, the preliminary result showed that compound 5, a polycysteine as a new type of radio-protector, had been developed with good efficacy and safety profile. Further study of the compound for potential use is ongoing.

Alexandrium pacificum is an organism that has an important impact on the aquaculture industry and human health. In this study, the digital gene expression approach was used to conduct a comparative analysis of differentially expressed genes (DEGs) that influence the explosive growth of A. pacificum following five treatment conditions: normal culture (C), high phosphorus and manganese (M), high irradiance (G), low phosphorus (P), and low nitrogen (N). Compared with the C conditions, a total of 265, 320, 185, and 150 DEGs were detected in the M, G, P, and N treatment groups, respectively. Clustering analysis suggested that A. pacificum acclimated to explosive growth using similar mechanisms in the M and G conditions. Analysis of DEGs showed that upregulation of genes associated with the pentose phosphate pathway and photosynthesis may contribute to explosive growth. Unigenes involved in the cell cycle were also found to be upregulated to promote cell division. The DEGs identified in this study may allow for the elucidation of molecular mechanisms responsible for the explosive growth of A. pacificum.

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