Katarzyna Turnau

Effect of heavy metal pollution on mycorrhizal colonization and function: physiological, ecological and applied aspects

Abstract High concentrations of heavy metals in soil have an adverse effect on micro-organisms and microbial processes. Among soil microorganisms, mycorrhizal fungi are the only ones providing a direct link between soil and roots, and can therefore be of great importance in heavy metal availability and toxicity to plants. This review discusses various aspects of the interactions between heavy metals and mycorrhizal fungi, including the effects of heavy metals on the occurrence of mycorrhizal fungi, heavy metal tolerance in these micro-organisms, and their effect on metal uptake and transfer to plants. Mechanisms involved in metal tolerance, uptake and accumulation by mycorrhizal hyphae and by endo- or ectomycorrhizae are covered. The possible use of mycorrhizal fungi as bioremediation agents in polluted soils or as bioindicators of pollution is also discussed.

The contribution of arbuscular mycorrhizal fungi in sustainable maintenance of plant health and soil fertility

Abstract. Beneficial plant–microbe interactions in the rhizosphere are primary determinants of plant health and soil fertility. Arbuscular mycorrhizas are the most important microbial symbioses for the majority of plants and, under conditions of P-limitation, influence plant community development, nutrient uptake, water relations and above-ground productivity. They also act as bioprotectants against pathogens and toxic stresses. This review discusses the mechanism by which these benefits are conferred through abiotic and biotic interactions in the rhizosphere. Attention is paid to the conservation of biodiversity in arbuscular mycorrhizal fungi (AMF). Examples are provided in which the ecology of AMF has been taken into account and has had an impact in landscape regeneration, horticulture, alleviation of desertification and in the bioremediation of contaminated soils. It is vital that soil scientists and agriculturalists pay due attention to the management of AMF in any schemes to increase, restore or maintain soil fertility.

Identification of arbuscular mycorrhizal fungi in soils and roots of plants colonizing zinc wastes in southern Poland

Abstract Analysis of the community of arbuscular mycorrhizal (AM) fungi in roots of Fragaria vesca growing in a heavy metal contaminated site was carried out on a Zn waste site near Chrzanow (southern Poland). The waste substratum was characterized by high contents of Pb, Zn, Cd, Cu and As, and by low levels of N, P and organic matter. Spores of Glomales were isolated by wet sieving and DNA was isolated from individual spores. Nested polymerase chain reaction (PCR) with taxon-specific primers was used to identify the species Glomus mosseae, Glomus intraradices and Glomus claroideum. Spores of other fungi were morphologically characterized and new taxon-discriminating molecular probes were developed for two of them (Glomus sp. HM-CL4 and HM-CL5) based on variations in the large ribosomal subunit (25S rDNA). High sequence similarities were found between Glomus sp. HM-CL4 and Glomus gerdemanii, and between Glomus sp. HM-CL5 and Glomus occultum. The designed primers were used to characterize the population of AM fungi colonizing the roots of F. vesca collected from the Zn waste site. The analysis, carried out on roots stained with trypan blue, showed that the most effective colonizer was closely related to G. gerdemannii. G. claroideum and the G. occultum-like fungus were slightly less common whilst frequencies of G. intraradices and G. mosseae in roots were much lower. The analysis of mycorrhiza stained with rhodizoniate to localize heavy metal accumulation showed that the stain does not influence the PCR reaction. Seventy percent of the root samples containing positively stained fungal hyphae were found to be colonized by G. mosseae. The data obtained demonstrate the usefulness of nested PCR for studies carried out in polluted areas. It will enable selection of AM fungi which are able to colonize plant roots under heavy metal stress conditions, as well as the identification of fungi showing high in situ accumulation of potentially toxic elements.

Differential responses of ectomycorrhizal fungi to heavy metals in vitro.

Thirty-nine ectomycorrhizal isolates of Paxillus involutus, Pisolithus tinctorius, Suillus bovinus, S. luteus and S. variegatus were tested on cadmium, copper, nickel and zinc amended media to determine their in vitro tolerance, measured as inhibition of biomass production. Twenty-one isolates were from heavy metal polluted sites, whereas the others were from non-contaminated soils. There was a strong interspecific variation in metal tolerance. S. luteus, S. variegatus and P. tinctorius were more tolerant of Cu, Cd and Zn when compared with P. involutus, whereas the reverse was true for Ni. A high intraspecific heterogeneity in metal tolerance was also found. EC 50 values for isolates originating from polluted sites were not statistically different from EC 50 values for isolates originating from non-contaminated sites. The findings are discussed in relation to the potential benefits of ectomycorrhizal fungi in protecting their host plants from metal contamination.

Arbuscular mycorrhiza of Berkheya coddii and other Ni-hyperaccumulating members of Asteraceae from ultramafic soils in South Africa

The occurrence of arbuscular mycorrhiza (AM) in nickel-(Ni)-hyperaccumulating plants of the Asteraceae family growing on Ni-enriched ultramafic soils in South Africa was surveyed. All plants were found to be consistently colonised by AM fungi, with the abundant formation of arbuscules. Berkheya coddii, which is an important species for phytomining, formed well-developed mycorrhiza under greenhouse conditions. Plants cultivated under greenhouse conditions and inoculated with native fungi had a higher shoot biomass and Ni content than noninoculated plants. Inoculation of B. coddii with Glomus intraradices (BEG) was successful, but only plants with abundantly developed arbuscules showed increased yield. In other cases, shoot biomass was similar to noninoculated plants. Dense depositions localised on top of the arbuscules were often observed in roots collected from the field and from pot cultures.

Ericoid mycorrhizal fungi from heavy metal polluted soils: their identification and growth in the presence of zinc ions

Ericoid mycorrhizal fungi can alleviate heavy metal toxicity to their host plant, but the mechanisms that lie behind this increased tolerance are unknown. As a first step in the characterisation of two isolates of Oidiodendron maius from mycorrhizal roots of Vaccinium myrtillus growing in heavily contaminated soils, we investigated their taxonomic position, their mycorrhizal capabilities and their ability to grow in the presence of heavy metals. When growth was compared with isolates from non-polluted soils, a better performance was observed in the presence of increasing concentrations of zinc salts, especially at higher ion concentrations. The mechanisms of tolerance may include the production of mucilage and extracellular pigments.

Influence of restoration on arbuscular mycorrhiza of Biscutella laevigata L. (Brassicaceae) and Plantago lanceolata L. (Plantaginaceae) from calamine spoil mounds.

Abstract. The arbuscular mycorrhizal status of two plant species, Biscutella laevigata L. and Plantago lanceolata L., was investigated on calamine spoil mounds in Bolesław (southern Poland). Although B. laevigata is a member of the Brassicaceae, a family generally accepted as non-mycorrhizal, this species formed AM symbioses on both heavy metal-contaminated and non-contaminated sites. Besides vesicles and coils, arbuscules were also observed, especially in roots collected prior to seed maturity. Relative mycorrhizal root length and relative arbuscular richness were usually much higher in P. lanceolata than in B. laevigata but not absolute arbuscule richness. Roots of P. lanceolata showed higher colonisation than B. laevigata. Although roots were collected from plants in close proximity, no correlation in mycorrhizal parameters was found between the two species.

Toxic element filtering in Rhizopogon roseolus/Pinus sylvestris mycorrhizas collected from calamine dumps

Rhizopogon roseolus/Pinus sylvestris mycorrhizas collected from calamine dumps (rich in Cd, Zn and Pb) were analysed by electron energy loss spectroscopy (EELS) connected to a transmission electron microscope. The distribution of potentially toxic elements within selected mycorrhizas was shown. Complementary data were obtained by cytochemical tests revealing the distribution of polysaccharides (PATAg) and cysteine-rich proteins (Gomori-Swift reaction). The mycorrhizas investigated were characterized by the accumulation of Cd and Al in the fungal mantle and a gradual decrease of these elements was observed along the Hartig net towards the inside of the root, suggesting a filtering effect. Both of these elements were detected in the electron-opaque deposition in the vacuoles, in periplasmic spaces as well as in the extracellular material. A comparatively high level of these elements was found in the phenolic material of dead cortical cells. This was probably an additional source of toxic elements for the mycelium which was colonizing the tannin cells.

In situ Raman imaging of astaxanthin in a single microalgal cell

Raman imaging is shown to be a highly selective and sensitive method of studying in situ and in vivo astaxanthin distribution, concentration and molecular structure in the cyst form of the unicellular microalgae Haematococcus pluvialis.

Response of endangered plant species to inoculation with arbuscular mycorrhizal fungi and soil bacteria

Three endangered plant species, Plantago atrata and Pulsatilla slavica, which are on the IUCN red list of plants, and Senecio umbrosus, which is extinct in the wild in Poland, were inoculated with soil microorganisms to evaluate their responsiveness to inoculation and to select the most effective microbial consortium for application in conservation projects. Individuals of these taxa were cultivated with (1) native arbuscular mycorrhizal fungi (AMF) isolated from natural habitats of the investigated species, (2) a mixture of AMF strains available in the laboratory, and (3) a combination of AMF lab strains with rhizobacteria. The plants were found to be dependent on AMF for their growth; the mycorrhizal dependency for P. atrata was 91%, S. umbrosus-95%, and P. slavica-65%. The applied inocula did not significantly differ in the stimulation of the growth of P. atrata and S. umbrosus, while in P. slavica, native AMF proved to be the less efficient. We therefore conclude that AMF application can improve the ex situ propagation of these three threatened taxa and may contribute to the success of S. umbrosus reintroduction. A multilevel analysis of chlorophyll a fluorescence transients by the JIP test permitted an in vivo evaluation of plant vitality in terms of biophysical parameters quantifying photosynthetic energy conservation, which was found to be in good agreement with the results concerning physiological parameters. Therefore, the JIP test can be used to evaluate the influence of AMF on endangered plants, with the additional advantage of being applicable in monitoring in a noninvasive way the acclimatization of reintroduced species in nature.