AM Plants Research Articles

Effects of Arbuscular Mycorrhizal Fungus (Glomus veruciforme) on Changes of Some Physiological Parameters in Cadmium Treated Wheat Plants

Soil pollution by heavy metals has become a critical environmental concern due to its potential adverse ecological effects. In this study we have investigated the effect of arbuscular mycorrhizal fungus (Glomus veruciforme) on some physiological growth parameters, such as chlorophyll content, amount of total soluble sugar and total protein of wheat plants (Triticum aestivum L. cv. Azar2) and we compared these factors in mycorrhizal (AM) and non-mycorrhizal (non-AM) plants. The content of chlorophyll in the absence of Cd in AM-plants was higher than non-AM plants. In the presence of mycorrhiza the content of chlorophyll a and b was decreased by increase in Cd concentration in both AM and non-AM plants. Furthermore, the amount of total soluble sugars and total proteins of shoots and roots have been increased in parallel to exogenous Cd concentration. In roots of AM-plants, the increase of soluble sugars was more dramatic in the presence of 2500 microm, but in the roots of non-AM plants this increase was step-by-step. The increase of total soluble sugars was gradually and significant in shoots of both AM and non-AM plants. The content of total proteins in shoots was raised with the increased level ofCd treatment, gradually and non-significantly.

Effect of Cadmium Toxicity on the Level of Lipid Peroxidation and Antioxidative Enzymes Activity in Wheat Plants Colonized by Arbuscular Mycorrhizal Fungi

High concentrations of heavy metals in the soil have an adverse effect on micro-organisms and microbial processes. Mycorrhizas are among the extracellular strategies to avoid metal toxicity. In the present study, the effect of cadmium on lipid peroxidation and antioxidative enzymes activity of AM (with Glomus veruciforme, G. intraradices and G. etunicatum) and non-AM Wheat plants was investigated. Wheat plants (Triticum aestivum L. cv. Azar2) which have been colonized by above species, were used in this study. They have been exposed to different concentrations of cadmium chloride for 60 days. The test solution contained: 0 (control), 250, 750 and 2500 microm cadmium Toxicity symptoms such as chlorosis and necrosis appeared on the cadmium treated leaves. Activity of detoxifying enzymes Guaiacol peroxidase (GUPX) and Ascorbate peroxidase (APX) of mycorrhizal and non-mycorrhizal plants were increased. Also, the amount of malondialdehyde (MDA) increased in roots and shoots ofmycorrhizal and non-mycorrhizal plants significantly as a result of Cd treatment, but it was more dramatic in mycorrhizal ones.

Influence of salinity on the in vitro development of Glomus intraradices and on the in vivo physiological and molecular responses of mycorrhizal lettuce plants.

Increased salinization of arable land is expected to have devastating global effects in the coming years. Arbuscular mycorrhizal fungi (AMF) have been shown to improve plant tolerance to abiotic environmental factors such as salinity, but they can be themselves negatively affected by salinity. In this study, the first in vitro experiment analyzed the effects of 0, 50, or 100 mM NaCl on the development and sporulation of Glomus intraradices. In the second experiment, the effects of mycorrhization on the expression of key plant genes expected to be affected by salinity was evaluated. Results showed that the assayed isolate G. intraradices DAOM 197198 can be regarded as a moderately salt-tolerant AMF because it did not significantly decrease hyphal development or formation of branching absorbing structures at 50 mM NaCl. Results also showed that plants colonized by G. intraradices grew more than nonmycorrhizal plants. This effect was concomitant with a higher relative water content in AM plants, lower proline content, and expression of Lsp5cs gene (mainly at 50 mM NaCl), lower expression of the stress marker gene Lslea gene, and lower content of abscisic acid in roots of mycorrhizal plants as compared to nonmycorrhizal plants, which suggest that the AM fungus decreased salt stress injury. In addition, under salinity, AM symbiosis enhanced the expression of LsPIP1. Such enhanced gene expression could contribute to regulating root water permeability to better tolerate the osmotic stress generated by salinity.

Arbuscular mycorrhizal fungi can induce the production of phytochemicals in sweet basil irrespective of phosphorus nutrition

The potential of three arbuscular mycorrhizal fungi (AMF) to enhance the production of antioxidants (rosmarinic and caffeic acids, RA and CA) was investigated in sweet basil (Ocimum basilicum). After adjusting phosphorus (P) nutrition so that P concentrations and yield were matched in AM and non-mycorrhizal (NM) plants we demonstrated that Glomus caledonium increased RA and CA production in the shoots. Glomus mosseae also increased shoot CA concentration in basil under similar conditions. Although higher P amendments to NM plants increased RA and CA concentrations, there was higher production of RA and CA in the shoots of AM plants, which was not solely due to better P nutrition. Therefore, AMF potentially represent an alternative way of promoting growth of this important medicinal herb, as natural ways of growing such crops are currently highly sought after in the herbal industry.

Modulation of polyamine balance in Lotus glaber by salinity and arbuscular mycorrhiza

In this work we investigated the involvement of Glomus intraradices in the regulation of plant growth, polyamines and proline levels of two Lotus glaber genotypes differing in salt tolerance, after longterm exposure to saline stress. The experiment consisted of a randomized block design with three factors: (1) mycorrhizal treatments (with or without AM fungus); (2) two salinity levels of 0 and 200 mM NaCl; and (3) L. glaber genotype. Experiments were performed using stem cuttings derived from L. glaber individuals representing a natural population from saline lowlands. One of the most relevant results was the higher content of total free polyamines in mycorrhized plants compared to non-AM ones. Since polyamines have been proposed as candidates for the regulation of root development under saline situations, it is possible that AM plants (which contained higher polyamine levels and showed improved root growth) were better shaped to cope with salt stress. Colonization by G. intraradices also increased (Spd + Spm)/Put ratio in L. glaber roots. Interestingly, such increment in salt stressed AM plants of the sensitive genotype, was even higher than that produced by salinization or AM symbiosis separately. On the other hand, salinity but not mycorrhizal colonization influenced proline levels in both L. glaber genotypes since high proline accumulation was observed in both genotypes under salt stress conditions. Our results suggest that modulation of polyamine pools can be one of the mechanisms used by AM fungi to improve L. glaber adaptation to saline soils. Proline accumulation in response to salt stress is a good indicator of stress perception and our results suggest that it could be used as such among L. glaber genotypes differing in salt stress tolerance.

The arbuscular mycorrhizal fungus Glomus mosseae gives contradictory effects on phosphorus and arsenic acquisition by Medicago sativa Linn

Mycorrhizal fungi may play an important role in protecting plants against arsenic (As) contamination. However, little is known about the direct and indirect involvement of arbuscular mycorrhizal fungi (AMF) in detoxification mechanisms. A compartmented pot cultivation system ('cross-pots') is used here to investigate the roles of AMF Glomus mosseae in plant phosphorus (P) and As acquisition by Medicago sativa, and P-As interactions. The results indicate that fungal colonization dramatically increased plant dry weight by a factor of around 6, and also substantially increased both plant P and As contents (i.e. total uptake). Irrespective of P and As addition levels, AM plants had shoot and root P concentrations 2 fold higher, but As concentrations significantly lower, than corresponding uninoculated controls. The decreased shoot As concentrations were largely due to "dilution effects" that resulted from stimulated growth of AM plants and reduced As partitioning to shoots. The study provides further evidence for the protective effects of AMF on host plants against As contamination, and have uncovered key aspects of underlying mechanisms. The possible application of AMF in remediation practices is discussed.

Alleviation of salt stress in Lotus glaber by Glomus intraradices

Lotus glaber is a glycophytic, perennial legume from Europe that occurs widely in saline habitats. We evaluated the effect of mycorrhizal fungus colonization on the response to salt stress of two genotypes of L. glaber differing in their tolerance to salinity. The experiment consisted of a randomized block design with two factors: (1) mycorrhizal fungus treatments (with or without AM fungus) and (2) two salinity levels of 0 and 200 mM NaCl. Our results indicated that Glomus intraradices established a more efficient symbiosis with the tolerant than with the sensitive genotype. G. intraradices improved growth of L. glaber plants under saline conditions. They showed higher values of net growth, shoot/root and K+/Na+ ratios, and protein concentrations than controls. Tolerant AM plants also showed higher chlorophyll levels than non-AM ones. Prevention of Na+ accumulation in the plant and enhancement of K+ concentrations in roots observed in this work could be part of the general mechanism of salt stress alleviation of L. glaber by G. intraradices.

Response of Mycorrhizal Switchgrass to Phosphorus Fractions in Acidic Soil

In acidic soils, acquisition of phosphorus (P) by plants is limited because of low P availability and slight solubility. Arbuscular mycorrhial fungi (AMF) have the ability to access much of soil P and make it more available to plants. Therefore, pools of available P to mycorrhizal (AM) plants grown in acidic soil are usually higher than in nonmycorrhizal (nonAM) plants. Switchgrass (Panicum virgatum L.) was grown in five acidic soils (Lily, Porters, Tatum, Rayne, and Pacolet) containing various amounts of original P with four different isolates of AMF in a glasshouse. The different fractions of P in each soil were determined to assess their importance to plant acquisition by AM and non‐AM plants. Total and organic P fractions in soil were relatively high compared with other extractable P fractions that are considered available to plants (extractable fractions), but differences among soils in total and organic P were relatively narrow compared with extractable fractions. With the exception of G. intraradices, each of the AMF isolates used (Glomus clarum, Glomus etunicatum, Glomus intraradices, and Acaulospora mellea) enhanced growth to some extent when grown in each of the soils. However, the highest dry matter (DM) for each of the AM plants was soil dependent. Shoot concentrations of mineral nutrients generally increased in AM plants that enhanced growth. None of the AMF isolates was best for these acidic soils, nor for each P fraction or other soil characteristic measured. Extractable P fractions appeared to be more readily available to AM plants than nonextractable fractions. †R. B. Clark is now retired.

Spatial Variability of Arbuscular mycorrhizal Fungal Spores in Two Natural Plant Communities

Geostatistical techniques were used to assess the spatial patterns of spores of arbuscular mycorrhizal fungi (AMF) in soils from two contrasting plant communities: a salt marsh containing only arbuscular mycorrhizal and non-mycorrhizal plants in a distinct clumped distribution pattern and a maquis with different types of mycorrhiza where most plants were relatively randomly distributed. Also evaluated was the relationship between the spatial distribution of spores and AM plant distribution and soil properties. A nested sampling scheme was applied in both sites with sample cores taken from nested grids. Spores of AMF and soil characteristics (organic matter and moisture) were quantified in each core, and core sample location was related to plant location. Semivariograms for spore density indicated strong spatial autocorrelation and a patchy distribution within both sites for all AM fungal genera found. However, the patch size differed between the two plant communities and AM fungal genera. In the salt marsh, AM fungal spore distribution was correlated with distance to AM plants and projected stand area of AM plants. In maquis, spatial AM fungal spore distribution was correlated with organic matter. These results suggest that spore distribution of AMF varied between the two plant communities according to plant distribution and soil properties.

MYCORRHIZAL FUNGI INCREASE CHROMIUM UPTAKE BY SUNFLOWER PLANTS: INFLUENCE ON TISSUE MINERAL CONCENTRATION, GROWTH, AND GAS EXCHANGE

ABSTRACT As a potential phytoremediation system for phytoextraction of chromium (Cr), we evaluated the influence of the arbuscular mycorrhizal fungus Glomus intraradices on leaf tissue elemental composition, growth and gas exchange of sunflower (Helianthus annuus L.). Sunflower seedlings were either inoculated with mycorrhizal fungi (AM) or non-inoculated (Non-AM) and then exposed to two Cr species: {12 mmol of trivalent cation (Cr+3) [Cr(III)] or 0.1 mmol of divalent dichromate anion (Cr2O7 −) [Cr(VI)]}. Both Cr species depressed plant growth, decreased stomatal conductance (g s ) and net photosynthesis (A). However, Cr(VI) was more toxic than Cr(III) as indicated by early reduction in g s , and greater reduction in plant growth and arbuscule formation. Mycorrhizal fungi helped to partially alleviate Cr toxicity as indicated by greater growth in plants treated with either Cr species, and increased gas exchange of Cr(III) plants. With Cr(III), Cr concentrations were the same in tissue of AM and Non-AM plants, while Non-AM Cr(VI) treatments had higher Cr concentration than AM plants; however with both Cr species, the larger-sized AM plants had greater total Cr accumulation on a whole-plant basis. Chromium reduced leaf elemental nitrogen (N), phosphorus (P), and potassium (K), and increased aluminum (Al), iron (Fe), and zinc (Zn) uptake. Chromium-treated AM plants had higher K and decreased levels of Fe and Al than Non-AM plants. Except for the depression of arbuscular formation in Cr(VI) treated plants, high colonization occurred with either Cr species. While higher P may have contributed to mycorrhizal benefits with Cr(III) plants, it does not account for any AM benefits observed with Cr(VI) plants.

Enhanced tolerances of transgenic tobacco plants expressing both superoxide dismutase and ascorbate peroxidase in chloroplasts against methyl viologen‐mediated oxidative stress

AbstractIn order to better understand the role of antioxidant enzymes in plant stress protection mechanisms, transgenic tobacco (Nicotiana tabacum cv. Xanthi) plants were developed that overexpress both superoxide dismutase (SOD) and ascorbate peroxidase (APX) in chloroplasts. These plants were evaluated for protection against methyl viologen (MV, paraquat)‐mediated oxidative damage both in leaf discs and whole plants. Transgenic plants that express either chloroplast‐targeted CuZnSOD (C) or MnSOD (M) and APX (A) were developed (referred to as CA plants and AM plants, respectively). These plant lines were crossed to produce plants that express all three transgenes (CMA plants and AMC plants). These plants had higher total APX and SOD activities than non‐transgenic (NT) plants and exhibit novel APX and SOD isoenzymes not detected in NT plants. As expected, transgenic plants that expressed single SODs showed levels of protection from MV that were only slightly improved compared to NT plants. The expression of either SOD isoform along with APX led to increased protection while expression of both SODs and APX provided the highest levels of protection against membrane damage in leaf discs and visual symptoms in whole plants.

Effect of the arbuscular mycorrhizal symbiosis upon uptake of cesium and other cations by plants

Pot experiments were set up to determine the species-specific uptake of cesium (Cs) by mycorrhizal (AM) and non-mycorrhizal (non-AM) plants. Using stable Cs and K application, side-effects of mineral fertilization (K) on AM development and uptake of Cs and the other cations Na, Ca and Mg were investigated. AM colonization by the fungus Glomus mosseae led to a significant decrease in shoot Cs content of Agrostis tenuis from the first (4 weeks) to the third harvest (8 weeks). With regard to the root system, statistically significant differences were observed from the first (4 weeks) to the second harvest (6 weeks). Supply of additional K produced a significant decrease in Cs uptake by both AM and non-AM plants over a 10-week period. In the case of AM plant shoots, K fertilization did not very effectively reduce Cs uptake by A. tenuis. Cs contents of fertilized AM roots were similar to non-AM controls. Potassium application resulted in an increase in K content and a slight reduction in Na and Mg contents of shoots and roots. Without K fertilization, the Na content of non-AM controls was significantly enhanced over AM shoots. Shoot and root Ca contents were generally higher without than with K addition. Negative side-effects of K fertilization as a countermeasure to Cs uptake were not observed in relation to AM development. The intensity of colonization by G. mosseae was not significantly depressed by K treatment. AM development in plants appeared to decrease Cs uptake, at least at moderate nutrient levels. It is possible that Cs is sequestered by AM extraradical fungal hyphae and consequently not transferred to the plant to the extent found in non-AM roots.

Mycorrhizal fungi enhance accumulation and tolerance of chromium in sunflower ( Helianthus annuus)

Chromium (Cr) is a heavy metal risk to human health, and a contaminant found in agricultural soils and industrial sites. Phytoremediation, which relies on phytoextraction of Cr with biological organisms, is an important alternative to costly physical and chemical methods of treating contaminated sites. The ability of the arbuscular mycorrhizal fungus (AM),Glomus intraradices, to enhance Cr uptake and plant tolerance was tested on the growth and gas exchange of sunflower (Helianthus annuus L.). Mycorrhizal-colonized (AM) and non-inoculated (Non-AM) sunflower plants were subjected to two Cr species [trivalent cation (Cr3+) {Cr(III)}, and divalent dichromate anion (Cr2O7−) {Cr(VI)}]. Both Cr species depressed plant growth, decreased net photosynthesis (A) and increased the vapor pressure difference; however, Cr(VI) was more toxic. Chromium accumulation was greatest in roots, intermediate in stems and leaves, and lowest in flowers. Greater Cr accumulation occurred with Cr(VI) than Cr(III). AM enhanced the ability of sunflower plants to tolerate and hyperaccumulate Cr. At higher Cr levels greater mycorrhizal dependency occurred, as indicated by proportionally greater growth, higherA and reduced visual symptoms of stress, compared to Non-AM plants. AM plants had greater Cr-accumulating ability than Non-AM plants at the highest concentrations of Cr(III) and Cr(VI), as indicated by the greater Cr phytoextraction coefficient. Mycorrhizal colonization (arbuscule, vesicle, and hyphae formation) was more adversely affected by Cr(VI) than Cr(III), however high levels of colonization still occurred at even the most toxic levels. Arbuscules, which play an important role in mineral ion exchange in root cortical cells, had the greatest sensitivity to Cr toxicity. Higher levels of both Cr species reduced leaf tissue phosphorus (P). While tissue P was higher in AM plants at the highest Cr(III) level, tissue P did not account for mycorrhizal benefits observed with Cr(VI) plants.

Effects of mycorrhizal fungus isolates on mineral acquisition by Panicum virgatum in acidic soil

Plant ability to withstand acidic soil mineral deficiencies and toxicities can be enhanced by root-arbuscular mycorrhizal fungus (AMF) symbioses. The AMF benefits to plants may be attributed to enhanced plant acquisition of mineral nutrients essential to plant growth and restricted acquisition of toxic elements. Switchgrass (Panicum virgatum L.) was grown in pHCa (soil:10 mM CaCl2, 1 : 1) 4 and 5 soil (Typic Hapludult) inoculated with Glomus clarum, G. diaphanum, G. etunicatum, G. intraradices, Gigasporaalbida, Gi. margarita, Gi. rosea, and Acaulosporamorrowiae to determine differences among AMF isolates for mineral acquisition. Shoots of mycorrhizal (AM) plants had 6.2-fold P concentration differences when grown in pHCa 4 soil and 2.9-fold in pHCa 5 soil. Acquisition trends for the other mineral nutrients essential for plant growth were similar for AM plants grown in pHCa 4 and 5 soil, and differences among AMF isolates were generally higher for plants grown in pHCa 4 than in pHCa 5 soil. Both declines and increases in shoot concentrations of N, S, K, Ca, Mg, Zn, Cu, and Mn relative to nonmycorrhizal (nonAM) plants were noted for many AM plants. Differences among AM plants for N and Mg concentrations were relatively small (<2-fold) and were large (2- to 9-fold) for the other minerals. Shoot concentrations of mineral nutrients did not relate well to dry matter produced or to percentage root colonization. Except for Mn and one AMF isolate, shoot concentrations of Mn, Fe, B, and Al in AM plants were lower than in nonAM plants, and differences among AM plants for these minerals ranged from a low of 1.8-fold for Fe to as high as 6.9-fold for Mn. Some AMF isolates were effective in overcoming acidic soil mineral deficiency and toxicity problems that commonly occur with plants grown in acidic soil.

Growth and root colonization of mycorrhizal maize grown on acid and alkaline soil

Arbuscular mycorrhizal fungi often have wide adaptability over many soil environments. We have determined the effects of the AM fungi Glomus etunicatum WV579A (Ge), G. diaphanum WV579B (Gd) and G. intraradices WV894 (Gi) on growth and root colonization of maize ( Zea mays L.) grown on two acid (pH 4.2 and 4.5) and two alkaline (pH 7.8 and 8.0) soils. Shoot and root dry matter (DM), leaf area (LA), and root length (RL) were higher for mycorrhizal (AM) than for nonmycorrhizal (nonAM) plants grown on all soils, and plants grown on alkaline soil had higher DM than plants grown on acid soil. Shoot and root DM followed a sequence of Ge > Gd≥Gi > nonAM for plants grown on the alkaline soil. The AM isolates enhanced DM of plants grown on acid soil, and differences among isolates were minor. Differences between AM and nonAM plants for total LA and RL were greater than for DM. Specific LA values for AM plants were consistently higher than for nonAM plants, while specific RL values for AM plants were only slightly higher than nonAM plants. Roots with arbuscules or vesicles was nil to low for plants grown on acid soil and relatively high for plants grown on alkaline soil. Roots with hyphal infection varied with type of soil and AM isolate, and was considerably higher than arbuscules or vesicles for plants grown on acid soil. Root hyphal infection appeared to be more important than arbuscules for growth enhancement of plants on acid soil. The AM isolates used were effective in enhancing growth of plants on both acid and alkaline soils showing wide adaptability to broad soil pH conditions.

Photosynthesis and nutrient-use efficiency of barley in response to low arbuscular mycorrhizal colonization and addition of phosphorus.

The effects of arbuscular mycorrhizal infection by Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe on growth and photosynthesis of barley (Hordeum vulgare L. cv. Manitou) were investigated in sand culture at five levels of calcium phosphate (50, 100, 200, 400 and 800 mg P kg(-1) ). Mycorrhizal infection was low and varied with P supply, declining from 3.3% at 50 mg P kg(-1) to 1.5% at the highest P concentration. In general, there were small differences in biomass between mycorrhizal (+AM) and non-mycorrhizal (-AM) barley but a significant reduction in dry mass of senesced leaves occurred in the +AM plants. Leaf P concentrations increased with P application, but did not differ between + AM and -AM plants. Although there were no differences in dry mass between + AM and -AM plants at 50 mg P kg(-1) , it was at this lowest P supply that +AM plants had higher rates of photosynthesis and greater P-use and N-use efficiencies. The mycorrhizal enhancement of maximum photosynthetic rate at the lowest P level was associated with a higher stomatal conductance, but was not related to increased leaf P or to changes in photon yield or the ratio of variable (FV) to maximum (FM) chlorophyll fluorescence.