Iris Charvat

Heavy-metal stress and developmental patterns of arbuscular mycorrhizal fungi.

ABSTRACT The rate of global deposition of Cd, Pb, and Zn has decreased over the past few decades, but heavy metals already in the soil may be mobilized by local and global changes in soil conditions and exert toxic effects on soil microorganisms. We examined in vitro effects of Cd, Pb, and Zn on critical life stages in metal-sensitive ecotypes of arbuscular mycorrhizal (AM) fungi, including spore germination, presymbiotic hyphal extension, presymbiotic sporulation, symbiotic extraradical mycelium expansion, and symbiotic sporulation. Despite long-term culturing under the same low-metal conditions, two species, Glomus etunicatum and Glomus intraradices, had different levels of sensitivity to metal stress. G. etunicatum was more sensitive to all three metals than was G. intraradices. A unique response of increased presymbiotic hyphal extension occurred in G. intraradices exposed to Cd and Pb. Presymbiotic hyphae of G. intraradices formed presymbiotic spores, whose initiation was more affected by heavy metals than was presymbiotic hyphal extension. In G. intraradices grown in compartmentalized habitats with only a portion of the extraradical mycelium exposed to metal stress, inhibitory effects of elevated metal concentrations on symbiotic mycelial expansion and symbiotic sporulation were limited to the metal-enriched compartment. Symbiotic sporulation was more sensitive to metal exposure than symbiotic mycelium expansion. Patterns exhibited by G. intraradices spore germination, presymbiotic hyphal extension, symbiotic extraradical mycelium expansion, and sporulation under elevated metal concentrations suggest that AM fungi may be able to survive in heavy metal-contaminated environments by using a metal avoidance strategy.

Effects of Metal Phytoextraction Practices on the Indigenous Community of Arbuscular Mycorrhizal Fungi at a Metal-Contaminated Landfill

ABSTRACT Phytoextraction involves use of plants to remove toxic metals from soil. We examined the effects of phytoextraction practices with three plant species (Silene vulgaris, Thlaspi caerulescens, and Zea mays) and a factorial variation of soil amendments (either an ammonium or nitrate source of nitrogen and the presence or absence of an elemental sulfur supplement) on arbuscular mycorrhizal (AM) fungi (Glomales, Zygomycetes) at a moderately metal-contaminated landfill located in St. Paul, Minn. Specifically, we tested whether the applied treatments affected the density of glomalean spores and AM root colonization in maize. Glomalean fungi from the landfill were grouped into two morphotypes characterized by either light-colored spores (LCS) or dark-colored spores (DCS). Dominant species of the LCS morphotype were Glomus mosseae and an unidentified Glomus sp., whereas the DCS morphotype was dominated by Glomus constrictum. The density of spores of the LCS morphotype from the phytoremediated area was lower than the density of these spores in the untreated landfill soil. Within the experimental area, spore density of the LCS morphotype in the rhizosphere of mycorrhizal maize was significantly higher than in rhizospheres of nonmycorrhizal S. vulgaris or T. caerulescens. Sulfur supplement increased vesicular root colonization in maize and exerted a negative effect on spore density in maize rhizosphere. We conclude that phytoextraction practices, e.g., the choice of plant species and soil amendments, may have a great impact on the quantity and species composition of glomalean propagules as well as on mycorrhiza functioning during long-term metal-remediation treatments.

In vitro propagation and life cycle of the arbuscular mycorrhizal fungus Glomus etunicatum

Progress in understanding the biology of arbuscular mycorrhizal fungi is hampered by the limited number of species that can be successfully propagated and studied in vitro . We report the establishment of monoxenic cultures of Glomus etunicatum in association with excised Ri T-DNA transformed carrot roots. The fungus can be propagated in vitro using monoxenically formed resting spores and/or colonized root fragments. Modified Whites medium buffered with 10 mM MES (pH 6) or MOPSO (pH 6.5) was most optimal for the host root growth as well as for G. etunicatum spore germination and mycorrhiza formation. The number of resting spores formed in vitro correlated positively with the length of roots occupied by arbuscular mycorrhizal structures, including arbuscules and vesicles. Spores first appeared in dual cultures within two weeks of root inoculation. Sporulation was asynchronous and continued until root senescence. Under applied culture conditions, spores achieved mature appearance within 5–7 d after their initiation. Approximately 6% of monoxenic spores were aborted at different stages of their development. Although G. etunicatum spores formed in vitro exhibited general morphological and anatomical similarity to soil-borne inoculum, they were significantly smaller and had thicker spore walls than their soil-borne counterparts. Caution should, therefore, be exercised in utilizing the in vitro system as a model of growth and development of glomalean fungi in soil.

Vesicular arbuscular mycorrhizae in floating wetland mat communities dominated by Typha

Low levels of vesicular arbuscular mycorrhizae were present in floating mats dominated by clones of Typha angustifolia L., T. x glauca Godr., and T. latifolia L. Floating mats composed of rhizomes (underwater-ground stems with high starch accumulation), roots, decaying organic matter, and wind deposited soil, easily supported human activities. The majority of roots isolated from the root cores were connected to Typha rhizomes. Tests employing the gridline intersect method, intensity, spore counts and most probable number (MPN) were used to define the level of colonization. Mycorrhizal colonization from the T. angustifolia and T. x glauca clones averaged 4 to 5%, while the T. latifolia clone averaged 13%. When colonization was encountered, intensities varied from a high of 3.0 to a low of 0.4 on a sclae of 0 to 4. Although arbuscules were not found, abundant hyphae, vesicles and spores indicated that presumed facultative associations occurred between the vesicular arbuscular fungi and the indicated that presumed facultative associations plant communities found on floating mats. The mycorrhizal fungi identified from these communities in cluded Glomus albidum Walker & Rhodes, G. caledonium (Nicol. & Gerd.) Trappe & Gerdemann, G. etunicatum Becker & Gerdemann, and G. microcarpum Tul. & Tul. Spore counts ranged from 16 to 76 spores per gram dried organic soil. The recolonization ability of VAM propagules by way of a most probable number bioassay with maize yielded numbers that ranged from zero to 96 propagules per gram soil, with G. etunicatum the only species recovered.

The mycorrhizal status of an emergent aquatic, Lythrum salicaria L., at different levels of phosphorus availability

Abstract The relationship between nutrient availability and mycorrhizal status has been well studied for terrestrial plant species, but has been examined rarely in aquatic and emergent aquatic species. The purpose of this study was to determine the effect of phosphorus availability on the arbuscular mycorrhizal (AM) status of an emergent aquatic, Lythrum salicaria L. L.salicaria was grown in hydroponic sand culture at five phosphorus concentrations (0, 100, 1000, 10 000, and 47 500 μg PO4/l nutrient solution) for 49 days with or without mycorrhizal inoculum obtained from wetland soil. Inoculated plants at the lowest three phosphorus concentrations were colonized by AM, whereas there was no colonization of plants grown at the highest two phosphorus concentrations. Colonization by AM fungi occurred in conjunction with symptoms of phosphorus deficiency in L. salicaria under experimental conditions: plants at the lowest three phosphorus concentrations had lower biomass and higher root: shoot weight ratios than plants at the highest two concentrations. However, total biomass and internal phosphorus concentration did not differ between inoculated and control plants. Further studies are needed under conditions more closely mimicking natural dynamics.

An ultrastructural study of acid phosphatase localization in cells ofPhaseolus vulgaris phloem by the use of the azo dye method

The localization of acid phosphatase was studied in the sieve elements and companion cells in the phloem tissue of the bean, Phaseolus vulgaris L. The various organelles in the two kinds of cell showed fine granules of the azo dye as the final reaction product. The aggregated smooth endoplasmic reticulum displayed the dye particularly consistently. The dye was also present in the plasmodesmata and in the contents of the sieve plate pores. The reaction product was conspicuous in the cell walls and tended to be concentrated in the middle lamella and in the nacreous wall layer of the differentiating sieve elements.

Activities and isozymes of acid phosphatase in Schizophyllum commune: a re-examination

Specific activities and isozymes of acid phosphatase (AcPase) were analyzed in colonies of Schizophyllum commune, a basidiomycete. Isogenic strains examined included two homokaryons, the dikaryon formed from them, and Bmut, a homokaryon with a primary mutation in the B incompatibility factor. In the homokaryons and the dikaryon AcPase activity increased with age to a peak at nine days and then declined; however, the activity of Bmut continued to rise after the ninth day. Two bands of activity were always present in polyacrylamide gels of extracts from all four strains at all ages analyzed. However, a third band appeared at different times in aging colonies of the homokaryons versus the dikaryon. A plot of the log of the mobility of the isozymes versus gel concentration provided evidence that these isozymes were primarily charge isomers, hence, not likely the result of proteolysis. These results are in contrast to the numerous isozymes of AcPase observed by Wang and Raper for several strains of Schizophyllum. We think their studies contain artifacts produced by the procedures they used.