Arsenite transporters expression in rice (Oryza sativa L.) associated with arbuscular mycorrhizal fungi (AMF) colonization under different levels of arsenite stress

As a silicon hyperaccumulator, lowland rice takes up higher levels of As than many other plants due to silicic acid and arsenite sharing the same transporters (Lsi1 and Lsi2). Glomus intraradices (AH01) was inoculated to rice under different arsenite concentrations (0, 2 and 8 μM) in order to investigate the interactions between arbuscular mycorrhizal fungus and rice on the accumulation of arsenite. The relative mRNA expressions of Lsi1 and Lsi2 resulted in a down-regulating trend in mycorrhizal plants. Under 2 μM arsenite treatments, Lsi1 and Lsi2 were significantly decreased, by 0.7-fold (P < 0.05) and 0.5-fold (P < 0.01), respectively, in mycorrhizal plants when compared with non-mycorrhizal plants. This led to the decrease of arsenite uptake per unit of root dry mass. No organic As species were detected in both roots and shoots. The As(III)/As(V) ratios indicated that mycorrhizal plants immobilized most of the arsenite proportion in the roots and prevented its translocation from the roots to the shoots.     

The effect of mycorrhiza on the growth and elemental composition of Ni-hyperaccumulating plant Berkheya coddii Roessler

The effect of arbuscular mycorrhizal fungi (AMF) on growth and element uptake by Ni-hyperaccumulating plant, Berkheya coddii, was studied. Plants were grown under laboratory conditions on ultramafic soil without or with the AM fungi of different origin. The AM colonization, especially with the indigenous strain, significantly enhanced plants growth and their survival. AMF affected also the elemental concentrations that were studied with Particle-induced X-ray emission (PIXE). AMF (i) increased K and Fe in shoots, Zn and Mn in roots, P and Ca both, in roots and shoots; (ii) decreased Mn in shoots, Co and Ni both, in shoots and roots. Due to higher biomass of mycorrhizal plants, total Ni content was up to 20 times higher in mycorrhizal plants compared to the non-mycorrhizal ones. The AMF enhancement of Ni uptake may therefore provide an improvement of a presently used technique of nickel phytomining.     

DDT uptake by arbuscular mycorrhizal alfalfa and depletion in soil as influenced by soil application of a non-ionic surfactant

A greenhouse pot experiment was conducted to investigate the colonization of alfalfa roots by the arbuscular mycorrhizal (AM) fungus Glomus etunicatum and application of the non-ionic surfactant Triton X-100 on DDT uptake by alfalfa and depletion in soil. Mycorrhizal colonization led to an increase in the accumulation of DDT in roots but a decrease in shoots. The combination of AM inoculation and Triton X-100 application enhanced DDT uptake by both the roots and shoots. Application of Triton X-100 gave much lower residual concentrations of DDT in the bulk soil than in the rhizosphere soil or in the bulk soil without Triton X-100. AM colonization significantly increased bacterial and fungal counts and dehydrogenase activity in the rhizosphere soil. The combined AM inoculation of plants and soil application of surfactant may have potential as a biotechnological approach for the decontamination of soil polluted with DDT.     

Propiconazole inhibits the sterol 14α-demethylase in Glomus irregulare like in phytopathogenic fungi

The increasing concentrations impact (0.02, 0.2 and 2 mg L⁻¹) of a Sterol Biosynthesis Inhibitor (SBI) fungicide, propiconazole, was evaluated on development and sterol metabolism of two non-target organisms: mycorrhizal or non-mycorrhizal transformed chicory roots and the arbuscular mycorrhizal fungus (AMF) Glomus irregulare using monoxenic cultures. In this work, we provide the first evidence of a direct impact of propiconazole on the AMF by disturbing its sterol metabolism. A significant decrease in end-products sterols contents (24-methylcholesterol and in 24-ethylcholesterol) was observed concomitantly to a 24-methylenedihydrolanosterol accumulation indicating the inhibition of a key enzyme in sterol biosynthesis pathway, the sterol 14α-demethylase like in phytopathogenic fungi. A decrease in end-product sterol contents in propiconazole-treated roots was also observed suggesting a slowing down of the sterol metabolism in plant. Taken together, our findings suggest that the inhibition of the both AM symbiotic partners development by propiconazole results from their sterol metabolism alterations.     

Interactions between arbuscular mycorrhizae and heavy metals under sand culture experiment

A sand culture experiment was established to determine interactions between arbuscular mycorrhizae and heavy metals. Mycorrhizal infection rates, spore densities, maize root and shoot weights, and heavy metal contents in maize were as indexes of responses of arbuscular mycorrhizal fungi (Acaulospora laevis, Glomus caledonium and Glomus manihotis) to heavy metals (Cu and Cd). The mycorrhizal infection rates of G. caledonium were the highest among these three mycorrhizal fungi, but the sporulating ability of G. caledonium was the poorest in the heavy metal treatments. The shoot and root weights of non-mycorrhizal plants were usually greater than those of mycorrhizal plants when the Cu concentrations in solutions are less than 3 mg l(-1) or Cd concentrations less than 1 mg l(-1). When Cd concentrations were 0.5 and 1 mg(-1), the root and shoot weights of plants inoculated with A. laevis were significantly (p < 0.05) lower than those of other treatments. Copper concentrations in shoots of mycorrhizal plants were higher than those of non-mycorrhizal ones at all Cu concentrations in solution, especially at low Cu concentrations. As to A. laevis, Cu concentrations in roots and shoots of the host were higher than those of non-mycorrhizal plants in these treatments. Thus A. laevis was sensitive to Cu and Cd, especially Cd, and G. caledonium was more tolerant to these two heavy metals. It is suggested that G. caledonium might be a promising mycorrhizal fungus for bioremediation of heavy metal contaminated soil.     

The arbuscular mycorrhizal fungus Glomus mosseae can enhance arsenic tolerance in Medicago truncatula by increasing plant phosphorus status and restricting arsenate uptake

A pot experiment examined the biomass and As uptake of Medicago truncatula colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae in low-P soil experimentally contaminated with different levels of arsenate. The biomass of G. mosseae external mycelium was unaffected by the highest addition level of As studied (200 mg kg⁻¹) but shoot and root biomass declined in both mycorrhizal and non-mycorrhizal plants, indicating that the AM fungus was more tolerant than M. truncatula to arsenate. Mycorrhizal inoculation increased shoot and root dry weights by enhancing host plant P nutrition and lowering shoot and root As concentrations compared with uninoculated plants. The AM fungus may have been highly tolerant to As and conferred enhanced tolerance to arsenate on the host plant by enhancing P nutrition and restricting root As uptake.     

Effect of arbuscular mycorrhizal fungus (Glomus caledonium) on the accumulation and metabolism of atrazine in maize (Zea mays L.) and atrazine dissipation in soil

Effects of an arbuscular mycorrhizal (AM) fungus (Glomus caledonium) on accumulation and metabolism of atrazine in maize grown in soil contaminated with different concentrations of atrazine were investigated in a series of pot experiments. Roots of mycorrhizal plants accumulated more atrazine than non-mycorrhizal roots. In contrast, atrazine accumulation in shoot decreased in mycorrhizal compared with non-mycorrhizal plants. No atrazine derivatives were detected in the soil, either with or without mycorrhizal colonization. However, atrazine metabolites, deethylatrazine (DEA) and deisopropylatrazine (DIA), were detected in plant roots and the AM colonization enhanced the metabolism. After plant harvest atrazine concentrations decreased markedly in the soils compared to the initial concentrations. The decreases were the most in rhizosphere soil and then near-rhizosphere soil and the least in bulk soil. Mycorrhizal treatment enhanced atrazine dissipation in the near-rhizosphere and bulk soils irrespective of atrazine application rates.     

Arbuscular mycorrhizal fungi can decrease the uptake of uranium by subterranean clover grown at high levels of uranium in soil

Subterranean clover inoculated or not with the arbuscular mycorrhizal (AM) fungus Glomus intraradices was grown on soil containing six levels of 238U in the range 0-87 mg kg(-1). Increasing U concentration in soil enhanced the U concentration in roots and shoots of both mycorrhizal and nonmycorrhizal plants but had no significant effects on plant dry matter production or root AM colonization. Mycorrhizas increased the shoot dry matter and P concentration in roots and shoots, while in most cases, it decreased the Ca, Mg and K concentrations in plants. The AM fungus influenced U concentration in plants only in the treatment receiving 87 mg U kg(-1) soil. In this case, U concentration in shoots of nonmycorrhizal plants was 1.7 times that of shoots of mycorrhizal plants. These results suggested that mycorrhizal fungi can limit U accumulation by plants exposed to high levels of U in soil.     

Uptake of Zn by arbuscular mycorrhizal white clover from Zn-contaminated soil

A randomised block glasshouse pot experiment compared the growth and Zn uptake of mycorrhizal and nonmycorrhizal white clover plants grown in a sterile soil/sand mixture containing 25 mg Zn kg(-1) to which five application rates of Zn (as ZnSO4) from 0 to 400 mg kg(-1) were made. Two mycorrhizal inocula infected roots from the field and from clover trap cultures, were compared. Mycorrhizal infection (ranging from 33% to 46% of total root length) and Zn application had little effect on plant growth. Increasing Zn application rate led to increased uptake of Zn in roots and shoots (especially roots), but the increases were significantly greater in non-mycorrhizal controls than in mycorrhizal treatments. In contrast, P uptake was higher in mycorrhizal than in non-mycorrhizal plants. Plants that received trap culture inoculum had significantly lower Zn uptake than those that received field inoculum. The results indicate that mycorrhizal infection may have exerted some protective effect against plant Zn accumulation at the range of soil Zn concentrations studied and may have immobilised Zn in or near the roots to some extent. However, this mycorrhizal effect cannot be explained simply by tissue dilution, hyphal sequestration or root immobilisation of Zn.     

Growth and nutrient uptake of arbuscular mycorrhizal maize in different depths of soil overlying coal fly ash

Application of topsoil over phytotoxic mine wastes is often practised to establish perennial plant communities on minespoil areas. In China, population pressure encourages attempts to remediate such areas by growing arable crop plants, but efforts to establish agricultural crops often fail. We report an outdoor pot experiment that compared the effects of two arbuscular mycorrhizal (AM) fungi, Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe and G. versiforme (Karsten) Berch, on the growth and nutrient uptake of maize (Zea mays L.) grown in different depths of soil layer overlying coal fly ash. Colonization by both AM fungi increased plant growth compared with non-mycorrhizal controls, with G. mosseae giving higher yields of maize than G. versiforme at the same depths of soil. Increasing soil depth led to increased plant yields. Mycorrhizal plants absorbed more nutrients than non-mycorrhizal controls, and translocated less Na to the shoots, perhaps protecting the plants from excessive Na accumulation. These preliminary results indicate that arbuscular mycorrhizas may make a substantial contribution to successful crop establishment in soils overlying areas of coal fly ash.     

Interactions of Trametes versicolor, Coriolopsis rigida and the arbuscular mycorrhizal fungus Glomus deserticola on the copper tolerance of Eucalyptus globulus

The presence of high levels of Cu in soil decreases the shoot and root dry weights of Eucalyptus globulus. However, higher plant tolerance of Cu has been observed in the presence of the arbuscular mycorrhizal (AM) fungus Glomus deserticola. The hyphal length of G. deserticola was sensitive to low Cu concentrations, and the percentage of AM root colonisation and the metabolic activity of the AM fungus were also decreased by Cu. Therefore, a direct effect of Cu on the development of the AM fungus inside and outside the root cannot be ruled out. E. globulus colonised by G. deserticola had higher metal concentrations in the roots and shoots than do non-mycorrhizal plants; however, the absence of a higher root to shoot metal ratio in the mycorrhizal plants (1.70 ± 0.11) indicated that G. deserticola did not play a filtering/sequestering role against Cu. The saprobe fungi Coriolopsis rigida and Trametes versicolor were able to remove Cu ions from the asparagine–glucose growth media. However, plants inoculated with C. rigida and T. versicolor did not accumulate more Cu than non-inoculated controls, and the growth of the plant was not increased in the presence of these fungi. However, C. rigida increased the shoot dry weight, AM root length colonisation, and metabolic mycelial activity of plants colonised with G. deserticola in the presence of Cu; only this saprobe-AM fungus combination increased the tolerance of E. globulus to Cu. Inoculation with G. deserticola and C. rigida increased the E. globulus Cu uptake to levels reached by hyperaccumulative plants.     

Metallophyte status of violets of the section Melanium

Violets from metal-enriched soils have controversially been described as both heavy-metal accumulators and excluders in the literature. The present study solves the issue for violets of the section Melanium (zinc violets, Viola lutea ssp. calaminaria and V. lutea ssp. westfalica; hartsease or wild pansy, Viola tricolor; and mountain pansy, V. lutea). The aims were to determine the concentrations of heavy metals in the soil and in the roots and shoots of field-collected plants, to evaluate the potential impact of colonisation by arbuscular mycorrhizal fungi on heavy-metal concentrations in the plant tissues, and to quantitatively define the localisation of the elements in root cross-sections. When these violets grow in low-metal soils, higher concentrations of the heavy metals were found in the roots and shoots than in the soil, whereas the opposite was seen in samples from high-metal soils. Under all field conditions examined, the roots of all of these species were colonised by arbuscular mycorrhizal fungi. However, V. tricolor was marginally colonised when the concentrations of Zn and P were higher in the soil. Determination of the spatial distribution of the elements in root cross-sections of these violets indicates tissue-specific deposition of elements within the vascular tissue, the cortex, and the rhizodermis. These data indicate that violets of the section Melanium are heavy-metal excluders.     

Potential contribution of arbuscular mycorrhiza to cadmium immobilisation in soil

The contribution of arbuscular mycorrhiza (AM) to immobilisation of Cd in substrate was studied in two experiments. In the first experiment, substrates prepared by cultivating tobacco, either non-mycorrhizal or inoculated with the AM fungus Glomus intraradices were enriched with a range of Cd concentrations, and Cd toxicity in the substrates was assessed using root growth tests with lettuce as a test plant. The tests revealed lower Cd toxicity in the mycorrhizal than in the non-mycorrhizal substrate, and the difference increased with increasing total Cd concentration in the substrates. In the second experiment, extraradical mycelium (ERM) of G. intraradices exposed in vivo to Cd was collected and analysed on Cd concentration. The ERM accumulated 10–20 times more Cd per unit of biomass than tobacco roots. While Cd concentrations were lower in the biomass of mycorrhizal plants than of non-mycorrhizal plants, Cd immobilisation by ERM did not affect the total Cd content in mycorrhizal tobacco.

It is concluded that mycorrhiza may decrease Cd toxicity to plants by enhancing Cd immobilisation in soil. The results therefore suggest a potential role of AM symbiosis in the phytostabilisation of contaminated soils, where high Cd availability inhibits plant growth.     

Uptake and distribution of phenanthrene and pyrene in roots and shoots of maize (Zea mays L.)

Polycyclic aromatic hydrocarbons as byproducts of carbon-based fuel combustion are an important group of pollutants with wide distribution in the environment. Polycyclic aromatic hydrocarbons are known as toxic compounds for almost all organisms. Different plant species can uptake polycyclic aromatic hydrocarbons by roots and translocate them to various aerial parts. The aim of this study is to investigate the uptake, translocation, and accumulation of pyrene and phenanthrene in maize under controlled conditions. Seeds were cultivated in perlite containing 25, 50, 75, and 100 ppm of phenanthrene and pyrene, and their concentrations in the roots and shoots of the plants were measured using high-performance liquid chromatography technique after 7, 14, and 21 days. The results revealed that phenanthrene naturally existed in maize and its concentration showed a time-dependent decrease in shoots and roots. In contrast, the concentration of pyrene was increased in the roots and reduced in the shoots. Although pyrene had higher uptake than phenanthrene in roots of maize, the translocation factor value for pyrene was lower than for phenanthrene. According to these findings, phenanthrene could be metabolized in maize in the shoot and root tissues, but pyrene had more tendency to be accumulated in roots.

     

Tolerance, uptake and removal of nitrobenzene by a newly-found remediation species Mirabilis jalapa L

The growth, photosynthesis rate, and ultrastructure of Mirabilis jalapa L. as a newly-found remediation species under stress of nitrobenzene (NB) and its uptake and removal of NB by the plants were investigated. The results showed that M. jalapa plants could endure contaminated soils by lower than 10.0 mg NB kg⁻¹ because there was no decrease in the total length of the plant roots, the maximum length of the hypocotyle, the length of the first seminal root, the height of the shoots and the dry biomass of the seedlings as well as the photosynthesis rate of the plants compared with those in the control. In particular, the growth of the plants could be significantly (P < 0.01) enhanced by 0.1 mg NB kg⁻¹ under unautoclaved and autoclaved soils. Ultrastructural observations on leaf cells of the plants found that these cells had smooth, clean and continuous cell membranes and cell walls, indicating that there was no obvious damage by NB in comparison with those in the control. Although the absorption of NB in shoots and roots of M. jalapa was weak, plant-promoted biodegradation of NB was considerable and the dominant contribution in the removal of NB from contaminated soils, suggesting the feasibility of M. jalapa applied to phytoremediation of NB contaminated soils.     

Arbuscular mycorrhizal fungi mediated uptake of lanthanum in Chinese milk vetch (Astragalus sinicus L.)

A glasshouse experiment was carried out to study the effect of mycorrhizal formation by Gigaspora margarita, Glomus intraradices or Acaulospora laevis on plant growth and lanthanum (La) uptake of Astragalus sinicus L. in soils spiked with La at five levels (0, 1, 5, 10 and 20 mg kg(-1)). La application decreased mycorrhizal infection frequency and activity of fungal succinate dehydrogenase and alkaline phosphatase. Increasing La concentrations in soil led to increased La accumulation in tissues of both mycorrhizal and non-mycorrhizal plants, but inoculation with Gig. margarita or G. intraradices reduced La concentrations in shoots and roots at higher concentrations of La in the soil. Plant biomass and P concentrations in shoots and roots were reduced by La application, but increased by inoculation with Gig. margarita or G. intraradices. The results showed that appropriate AM fungi colonization could be effective in alleviating La toxicity in A. sinicus.     

The arbuscular mycorrhizal fungus Glomus mosseae induces growth and metal accumulation changes in Cannabis sativa L

The effect of arbuscular mycorrhiza on heavy metal uptake and translocation was investigated in Cannabis sativa. Hemp was grown in the presence and absence of 100 microg g-1 Cd and Ni and 300 microg g-1 Cr(VI), and inoculated or not with the arbuscular mycorrhizal fungus Glomus mosseae. In our experimental condition, hemp growth was reduced in inoculated plants and the reduction was related to the degree of mycorrhization. The percentage of mycorrhizal colonisation was 42% and 9% in plants grown in non-contaminated and contaminated soil, suggesting a significant negative effect of high metal concentrations on plant infection by G. mosseae. Soil pH, metal bioavailability and plant metal uptake were not influenced by mycorrhization. The organ metal concentrations were not statistically different between inoculated and non-inoculated plants, apart from Ni which concentration was significantly higher in stem and leaf of inoculated plants grown in contaminated soil. The distribution of absorbed metals inside plant was related to the soil heavy metal concentrations: in plant grown in non-contaminated soil the greater part of absorbed Cr and Ni was found in shoots and no significant difference was determined between inoculated and non-inoculated plants. On the contrary, plants grown in artificially contaminated soil accumulated most metal in root organ. In this soil, mycorrhization significantly enhanced the translocation of all the three metals from root to shoot. The possibility to increase metal accumulation in shoot is very interesting for phytoextraction purpose, since most high producing biomass plants, such as non-mycorrhized hemp, retain most heavy metals in roots, limiting their application.     

Behavior of decabromodiphenyl ether (BDE-209) in soil: effects of rhizosphere and mycorrhizal colonization of ryegrass roots

A rhizobox experiment was conducted to investigate degradation of decabromodiphenyl ether (BDE-209) in the rhizosphere of ryegrass and the influence of root colonization with an arbuscular mycorrhizal (AM) fungus. BDE-209 dissipation in soil varied with its proximity to the roots and was enhanced by AM inoculation. A negative correlation (P < 0.001, R² = 0.66) was found between the residual BDE-209 concentration in soil and soil microbial biomass estimated as the total phospholipid fatty acids, suggesting a contribution of microbial degradation to BDE-209 dissipation. Twelve and twenty-four lower brominated PBDEs were detected in soil and plant samples, respectively, with a higher proportion of di- through hepta-BDE congeners in the plant tissues than in the soils, indicating the occurrence of BDE-209 debromination in the soil-plant system. AM inoculation increased the levels of lower brominated PBDEs in ryegrass. These results provide important information about the behavior of BDE-209 in the soil-plant system.     

Arbuscular mycorrhizal fungi can alleviate the adverse effects of chlorothalonil on Oryza sativa L

A glasshouse pot experiment was conducted to investigate the effect of the fungicide chlorothalonil on the growth of upland rice, in the absence or presence of the arbuscular mycorrhizal fungus (AMF) Glomus mosseae (NM and GM treatments). The plants were grown with three concentrations of chlorothalonil (0, 50 and 100 mg kg(-1) soil). Mycorrhizal colonization decreased significantly with increasing chlorothalonil concentrations. Plant biomass decreases were smaller in GM plants than in non-mycorrhizal (NM) plants. Mycorrhizal dependency was the highest with 50 mg kg(-1) chlorothalonil. Chlorothalonil affected physiological processes in upland rice irrespective of inoculation. Chlorothalonil at 50 and 100 mg kg(-1) increased ascorbate peroxidase (APX) activity and soluble protein concentrations in shoots and roots of NM upland rice. However, values of APX, catalase (CAT) and peroxidase (POD) were reduced more in GM plants than in NM plants. These results showed that chlorothalonil induced oxidative stress in upland rice and it is needed to evaluate the side effects of chlorothalonil on rice and AMF.     

Can arbuscular mycorrhizal fungi improve grain yield, As uptake and tolerance of rice grown under aerobic conditions?

The effects of arbuscular mycorrhizal fungi (AMF) - Glomus intraradices and G. geosporum on arsenic (As) and phosphorus (P) uptake by lowland (Guangyinzhan) and upland rice (Handao 502) were investigated in soil, spiked with and without 60 mg As kg⁻¹. In As-contaminated soil, Guangyinzhan inoculated with G. intraradices or Handao 502 inoculated with G. geosporum enhanced As tolerance, grain P content, grain yield. However, Guangyinzhan inoculated with G. geosporum or Handao 502 inoculated with G. intraradices decreased grain P content, grain yield and the molar ratio of grain P/As content, and increased the As concentration and the ratio of grain/straw As concentration. These results show that rice/AMF combinations had significant (p < 0.05) effects on grain As concentration, grain yield and grain P uptake. The variation in the transfer and uptake of As and P reflected strong functional diversity in AM (arbuscular mycorrhizal) symbioses.