Journal of Plant Process and Function

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Soil pollution with heavy metals is an important environmental problem which affects human and food health. Neotyphodium endophytes are a group of fungi which spend their entire life cycle within the aerial portion of many grass species without any symptoms, and increase host tolerance to biotic and abiotic stresses. In this study, two genotypes of tall fescue (75 B and 75 C) in two types (infected (E+) and non-infected (E-) by endophyte) were cultivated in a Ni contaminated soil at 0, 30, 90 and 180 mg Ni per kg with 3 replicates. After 2 months, Ni uptake of the root and shoot as well as chlorophyll and carotenoid content of the shoot were measured. Growth parameters including root and shoot wet weight and root to shoot weight ratio of plants were also measured at the end of the experiment. The results showed that endophytic fungi caused an increase in chlorophyll contents of the shoots in the both genotypes and an increase in Ni uptake only in genotype 75 B. Results also demonstrated that endophyte infection led to improvement in the growth and Ni tolerance within genotype 75 B of tall fescue under Ni stress. But in the genotype 75 C, in contrast, the E- plants showed more tolerance to Ni stress compared to E+ plants. It revealed that how the effects of endophyte infection in Festuca plants as the host were dependent on the host genotype.

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Heavy metal stress in plants may cause oxidative stresses and reactive oxygen species (ROS) production. To reduce this stress, plants use antioxidative defences, such as increasing the activity of antioxidant enzymes. In this study, the role of an arbuscular mycorrhizal (AM) fungi Glomus intraradices as a symbiotic microorganism with plant, was investigated in inducing tolerance to oxidative stress induced by Nickel heavy metal. Tall fescue plants were grown in soils containing 0, 30, 90, 180 ppm of Nickel, in two forms of infected to fungi (M+) and uninfected (M-) for 3 months. Experimental results showed that Nickel treatment caused reduction in growth parameters, where these parameter were higher in M+ plants than M- ones. Membrane electrolyte leakage was increased by the increase of Nickel concentration, and the increase was higher in M+ plants compared to M- plants. Results of measuring the activity of antioxidant enzymes showed that the presence of fungi had increased the activity of catalase (CAT), guaiacol peroxidase (GPX) and glutathione reductase (GR) enzymes against the toxic effect of Nickel, but this had not affected (increasing or decreasing) the activity of ascorbate peroxidase (APX) and superoxide dismutase (SOD) enzymes. These results demonstrated the negative effect on Glutathione-S-transferase (GST) enzyme. Precense of Glomus intraradices in M+ plants amplified the antioxidant system in Festuca plants and reduced the negative effects of Nickel treatment.

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Lolium perenne has symbiosis relationships with an important group of endophytes genus Neotyphodium. Agronomic traits of this plant and its resistance to biotic and abiotic stresses are affected by Neotyphodium spp., resulting to changes in its physiology and morphology. Effect of Nickel and endophyte symbiosis on growth parameters and nickel uptake in two different natural populations are investigated in this study. Each population consisted of two groups of plant (E+ and E- with or without endophyte). Treatments consisted of 0, 30, 90 and 180 mg Ni kg 1- soil), and growth parameters including root and shoot wet, dry weight and length, tiller number, and nickel uptake in root and shoot were evaluated after 3 months from treatment. After 3 months from treated plants, significant decrease in root and shoot biomass of E+ and E- plants was observed in 180 treatment and endophyte infection decreased the biomass plants. However, endophyte infection significantly improved the tillering ability of host ryegrass. Also, a significant increase in the Ni concentration of root and shoot was observed under Ni stress and the Ni concentration of E+ plants was 12.7% and 88.7% higher in root and shoot, respectively, than in E- plants. Results indicated decreases in root and shoot wet and dry weights were decreased in concentration 180 mg.kg-1 treatments, and root length in concentration 30 mg.kg-1. Greatest number of tillers observed in population 1 in 30 mg.kg-1 treatment. Nickel uptake was significantly increased in roots and shoots of both populations when soil Ni was increased. Nickel uptake of root and shoot in two populations of L. perenne plants was decreases in presence of with endophytes (E+ plants) which is considered as an important factor towards decrease in negative effects of this element. Population 1 with more shoot tiller and nickel uptake under stress conditions could be introduced as the suitable population to be cultivated in stress conditions.