Aims Ectomycorrhizal fungi can improve poplar growth and tolerance to heavy metal stress, and may be useful during the afforestation and phytoremediation of polluted regions with poplar trees. In this study, we determined the effects of the symbiotic interaction between Populus × canescens trees and Paxillus involutus strains different in their tolerance to lead. Methods In vitro inoculated and non-inoculated plants were treated with 0.75 mM Pb(NO 3 ) 2 . The root colonization rate of the two fungal strains, as well as their impacts on poplar health and lead accumulation were examined. Results Based on the colonization level, the roots were classified into one of three categories: non-mycorrhized, changed (ie, fungal cells were present on the root surface, but the Hartig net did not fully develop), and fully mycorrhized. The lead-tolerant P. involutus strain colonized roots better than the non-tolerant strain (ie, changed and fully mycorrhized roots). Moreover, plants inoculated with the tolerant fungal strain grew better than the control plants (217 % increase in dry weight over the controls), and accumulated lead in the roots and stems.Conclusions Inoculation of P. × canescens trees with a Pb-tolerant strain of P. involutus improves host plant growth and may increase Pb phytostabilization potential.

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Two-year-old embryogenic tissues (ET) of Picea omorika (Pančić) Purk. were successfully cryopreserved after preculture with sucrose, air-drying for 2 h, and freezing in liquid nitrogen (LN). The preculture protocol consisted of passaging the ET onto standard Litvay medium containing increasing concentrations of sucrose (0.25 M sucrose for 24 h, 0.5 M for 24 h, 0.75 M for 2 days, and 1.0 M for 3 days) for 7 days, at 25°C, and in the dark. The clumps were subsequently air-dried over silica gel, down to a 20% water content (based on fresh weight), placed in cryovials, and immersed in liquid nitrogen (LN) for 24 h. These were thawed at 42°C and progressively rehydrated in phytagel-solidified LM media containing decreasing concentrations of sucrose. After 3 weeks of in vitro culture, surviving clumps were friable and white in color, similar to their morphology prior to cryostorage. The frequency of bacterial and fungal contamination was higher if ET was frozen in LN-containing vials than in LN-free vials. This efficient cryopreservation protocol would be useful for the ex-situ conservation of P. omorika germplasm in gene banks at very low temperatures.