پیامد کاربرد قارچ مایکوریزا بر برخی ویژگی های بیوشیمیایی ارقام گندم در خاک آلوده به سرب

افزایش آلودگی خاک با فلزات سنگین یکی از مهم‌ترین موضوعات در سراسر جهان به شمار می‌رود که امروزه در کانون توجهات قرار گرفته است. سرب به‌عنوان یکی از خطرناک‌ترین فلزات سنگین و آلاینده‌های شیمیایی پایدار، بر محیط‌زیست به‌خصوص فعالیت‌های متابولیکی و فیزیولوژیکی موجودات زنده تاثیر می‌گذارد و در نهایت به‌سلامت محیط‌زیست و انسان آسیب‌های جدی وارد می‌کند. پژوهش حاضر با هدف بررسی اثر کاربرد و عدم کاربرد قارچ مایکوریزا (rhizophagus irregularis) بر میزان فعالیت برخی خصوصیات بیوشیمیایی 10 ژنوتیپ گندم در سه غلظت مختلف سرب (0، 218 و 437 میلی گرم بر کیلوگرم) در خاک انجام گردید. با افزایش غلظت سرب، میزان مالون دی آلدهید نیز افزایش یافت که در نتیجه‌ی تخریب سلول‌های گیاهی می‌باشد. مقادیر پرولین رقم پارس در هر دو تیمار عدم کاربرد و کاربرد قارچ مایکوریزا در غلظت 218 میلی‌گرم بر کیلوگرم سرب و نیز رقم سیروان در تیمار عدم کاربرد قارچ و غلظت 218 میلی گرم بر کیلوگرم سرب به ترتیب در بالاترین مقدار قرار داشت. فعالیت کاتالاز رقم بهار در تیمار عدم کاربرد قارچ با غلظت 218 میلی گرم بر کیلوگرم سرب در بیشترین سطح بود. رقم روشن در غلظت 218 میلی گرم بر کیلوگرم دارای فعالیت آنزیم آسکوربات پراکسیداز بالایی بود. پس ‌از این رقم، ارقام بک کراس روشن و پیشتاز در همین غلظت میزان بیش‌تری از فعالیت این آنزیم را به خود اختصاص دادند. مقدار پراکسید هیدروژن با تغییر غلظت سرب از 0 به 218 میلی گرم بر کیلوگرم کاهش نشان داد، درحالی‌که در غلظت 437 میلی گرم بر کیلوگرم مقدار آن افزایش داشت. با افزایش غلظت سرب میزان کلروفیل a کاهش و میزان کلروفیل b افزایش یافت. کاربرد قارچ مایکوریزا بر آنزیم‌های مالون دی آلدئید، پرولین، کاتالاز و پراکسید هیدروژن تاثیرگذار بود و سبب کاهش مقدار این آنزیم‌ها در مقایسه با شاهد شد.

Effect of Mycorrhizal Fungus Application on Some Biochemical Characters of Wheat Cultivars in Lead Contaminated Soil

Introduction: Nowadays, increasing soil contamination by heavy metals is one of the most important issues around the world, and is the focus of attention. Lead as the most dangerous heavy metal and persistent chemical pollutant affects the environment, especially the metabolic and physiological activities of organisms and ultimately cause serious damage to the environment and human health. The purpose of this study was to investigate the effect of mycorrhizal fungus (Rhizophagus irregularis) on some biochemical traits of 10 wheat genotypes in three different concentrations of lead heavy metal (0, 218 and 437 ppm) in soil.Material and Methods: The present study was conducted as factorial experiment based on randomized complete block design with three replications. The factors included lead in three concentrations (0, 218 and 437 mg / kg), mycorrhizal inoculum (addition and no addition), and 10 wheat genotypes (Shiraz, Sepahan, Sirvan, Back Cross Roshan, Marvdasht, Sivand, Bahar, Pars, Roshan, and Pishtaz). Soil samples were prepared from a depth of 025 cm of the research farm of Islamic Azad University, Karaj Branch. Samples were taken randomly. After soil drying and passing through a 2 mm sieve, they were transferred to the soil science laboratory to determine some of the physical and chemical properties. According to the soil test results, the soil was sandy loam, a semilight soil with 25% clay, 25% silt and 50% sand, with pH = 7.49 and salinity of 1.63 dS. m1, and also free of heavy metals. The soil was sterilized for four hours by an autoclave at the temperature of 121 °C and a pressure of 1.5 atm. After soil preparation, the lead was added to the soil at three concentrations of 0, 218 and 437 ppm, and stored in a preembedded bag with 60% moisture content to achieve a twoweek equilibrium. In order to inoculate the mycorrhizal fungus, after removal of 34 cm from the soil surface, Rhizophagus irregularis (35 g) was added to the soil surface, then 30 to 40 seeds were placed on the soil surface and covered with soil. In the control samples without mycorrhizal fungus, a certain amount of mycorrhizal fungus placed at 105 ºC to kill the fungus and then added to the pots.Results and Discussion: Malondialdehyde concentration increased by increasing the concentration of lead. The highest concentrations of proline were belonged to the level 218 ppm of lead, in Pars cultivar in both treatments of with and without mycorrhiza fungus as well as Sirvan cultivar in the treatment of without fungi, respectively. The activity of Catalase was highest in the treatment of 218 ppm of lead without fungus. Roshan cultivar also showed high levels of ascorbate peroxidase activity in 218 ppm of lead. Similar to cultivar, BC Roshan and Pishtaz cultivars also showed high ascorbate peroxidase activity in this concentration of lead. The amount of hydrogen peroxide was reduced by changing the concentration of lead from 0 to 218 ppm, while its amount increased at 437 ppm concentration. With increasing lead concentration, the amount of chlorophyll a decreased while chlorophyll b increased. Using mycorrhizal fungus, the amount of malondialdehyde, proline and hydrogen peroxide and catalase content decreased compared with control. It seems that lead, due to its concentration in the environment, leads to the induction of oxidative stress and the formation of free radicals and thus change in the amount of biochemical traits of wheat such as malondialdehyde, proline, hydrogen peroxide and chlorophyll a and b and activity of catalase and ascorbate peroxidase. The genotype of the plant is very important factor in tolerating the toxicity of lead, and it deals with various protective mechanisms. Not only the plant genotype but also environmental factors such as the use of mycorrhizal fungus are effective in reducing the harmful effects of lead, and helps plants tolerate the stress caused by lead toxicity.Conclusion: Lead in the soil causes changes in the biochemical content of wheat cultivars. The amount of change depends on the plant apos;s genotype, lead concentration, and other factors in the soil, such as symbiotic fungi. As shown in the present study, mycorrhizal fungus was effective in eliminating the negative effects of lead during symbiotic with wheat. It is suggested further studies to determine the concentration of lead and even other heavy metals in wheat genotypes and to compare with Iranian national standards in order to overcome the concerns about the entry of these metals into the diet.