The effect of arbuscular mycorrhizal fungus Glomus intraradices on some growth and physiological parameters in wheat (cv. Azar2) plants under cadmium toxicity

Cadmium is a non-essential element that negatively affects plant growth and its development. In this study, the effect of an arbuscular mycorrhizal (AM) fungus Glomus intraradices on some growth and physiological traits such as fresh and dry weight of root and shoot, photosynthetic pigments, total sugars, total protein content, lipid peroxidation and oxidative stress in wheat (Triticum aestivum L. cv. Azar2) plants under the toxic levels of cadmium was investigated. The experiment was performed by using two treatments (mycorrhizal and non-mycorrhizal) and four cadmium concentrations (0, 250, 750 and 2500 µM CdCl2). Plants received 40 mL nutrient solution (with half P content) three times a week and also 40 mL test solution (contained cadmium) three times a week, alternatively. Plants were grown in a growth chamber with temperatures ranging from 23 to 27ºC and a 14/10 light/dark period. Leaves and roots from 60-day-old plants were taken and used for investigation. Arbuscular mycorrhizal fungi had a significant influence on root and shoot fresh and dry weights, where the presence of AM fungus caused a decrease in the negative effect of Cd toxicity. Root length decreased due to an increase in Cd concentration, but there was no corresponding effect on the shoot length. Colonized plants showed less negative effect of Cd on their root length than non-AM plants. Determination of chlorophyll a and b content showed decreased chlorophyll content in both AM and non-AM plants by increasing Cd concentration, but this decrease in the mycorrhizal plants was lower than in non-mycorrhizal plants. By increasing in metal concentration, the content of total sugars and total proteins increased in both shoots and roots of AM plants. The amount of malondealdehyde (MDA) increased in roots and shoots of mycorrhizal and non-mycorrhizal plants under Cd toxicity, indicating lipid peroxidation. Activity of detoxifying enzymes, guaiacol peroxidase (GUPX) and ascorbate peroxidase (APX) in AM and non-AM plants increased but the increase of these activities in mycorrhizal plants was higher than non-mycorrhizal ones. Root length colonization was measured by gridline intersect method. Mycorrhizal colonization decreased due to the Cd exposure significantly. According to these results, it is suggested that this fungus (G. intraradices) can help wheat plants to tolerate Cd toxicity.