This review paper is focused predominantly on the role of the cell wall in the defense response of plants to trace metals. It is generally known that this compartment accumulates toxic divalent and trivalent metal cations both during their uptake by the cell from the environment and at the final stage of their sequestration from the protoplast. However, from results obtained in recent years, our understanding of the role played by the cell wall in plant defense response to toxic metals has markedly altered. It has been shown that this compartment may function not only as a sink for toxic trace metal accumulation, but that it is also actively modified under trace metal stress. These modifications lead to an increase in the capacity of the cell wall to accumulate trace metals and a decrease of its permeability for trace metal migration into the protoplast. One of the most striking alterations is the enhancement of the level of low-methylesterified pectins: the polysaccharides able to bind divalent and trivalent metal ions. This review paper will present the most recent results, especially those that are concerned with polysaccharide level, composition and distribution under trace metal stress, and describe in detail the polysaccharides responsible for metal binding and immobilization in different groups of plants (algae and higher plants). The review also contains information related to the entry pathways of trace metals into the cell wall and their detection methods.

SummaryDeveloping new strategies for crop plants to respond to drought is crucial for their innovative breeding. The down-regulation of nuclear cap-binding proteins in Arabidopsis renders plants drought tolerant. The CBP80 gene in the potato cultivar Desiree was silenced using artificial microRNAs. Transgenic plants displayed a higher tolerance to drought, ABA-hypersensitive stomatal closing, an increase in leaf stomata and trichome density, and compact cuticle structures with a lower number of microchannels. These findings were correlated with a higher tolerance to water stress. The level of miR159 was decreased, and the levels of its target mRNAs MYB33 and MYB101 increased in the transgenic plants subjected to drought. Similar trends were observed in an Arabidopsis cbp80 mutant. The evolutionary conservation of CBP80, a gene that plays a role in the response to drought, suggests that it is a candidate for genetic manipulations that aim to obtain improved water-deficit tolerance of crop plants.

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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.