جداسازی، شناسایی و تعیین فعالیت آنزیم ACC Deaminase باکتری های غالب ریزوسفر کلزا در خاکهای شور

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجو دوره دکتری گروه مهندسی خاک پردیس کشاورزی و منابع طبیعی دانشگاه تهران

2 دانشیار گروه مهندسی خاک پردیس کشاورزی و منابع طبیعی دانشگاه تهران

3 استادیار پژوهش موسسه تحقیقات خاک و آب

4 کارشناس موسسه تحقیقات خاک و آب

چکیده

بهره‌برداری صحیح از خاکهای شور برای نیل به حداکثر عملکرد گیاهان زراعی همواره از چالش‌های عمده بخش کشاورزی بوده است. گیاهان کاشته شده در این خاکها به طرق مختلف از شوری متأثر شده و به حداکثر رشد و عملکرد خود نمی‌رسند. یکی از راههای صدمه شوری به بعضی از گیاهان منجمله کلزا، تجمع اتیلن در ریشه است. تجمع اتیلن باعث کاهش رشد ریشه و در نتیجه افت عملکرد گیاه می‌شود. در صورت وجود باکتری‌هایی با توان تولید ACC deaminase در ریزوسفر، این امکان وجود دارد تا در این شرایط با تبدیل پیش‌ساز اتیلن (ACC) به آلفا- کتوبوتیرات و آمونیاک، سطح اتیلن در گیاه میزبان کاهش یابد. لذا با توجه به اهمیت گسترش سطح زیر کشت کلزا در ایران و لزوم کشت آن در اراضی شور و لب شور ضرورت داشت تا در اولین قدم، باکتری‌هایی با صفت مذکور از ریزوسفر کلزای کاشته شده در این اراضی جداسازی و شناسایی شوند. بدین منظور تعداد 21 نمونه مرکب خاک بهمراه ریشه گیاه کلزا از 21 منطقه تحت کشت آن در اراضی شور و نسبتاً شور استانهای قم و قزوین تهیه شد. پس از تعیین برخی مشخصات شیمیایی و بیولوژیکی نمونه‌های خاک، تعداد 105 جدایه از خاک ریزوسفری کلزا انتخاب گردید. براساس توانایی رشد جدایه‌ها در محیط حداقل DF حاوی ACC بعنوان تنها منبع نیتروژن مشخص گردید که تعداد 15 جدایه دارای توان تولید  ACC deaminase بودند. شناسایی این جدایه‌ها با استفاده از نتایج آزمونهای میکروسکوپی، فیزیولوژیکی و بیوشیمیایی مندرج در کتاب سیستماتیک باکتریولوژی Bergey نشان داد که کلیه جدایه‌ها در گروه سودوموناسهای فلورسنت قرار می‌گیرند. آزمون‌های مربوط به تعیین گونه نیز نشان داد که 14 جدایه متعلق به گونه  P. fluorescens بودند. در خصوص یکی از جدایه‌ها نیز به دلیل عدم تطابق نتایج با مندرجات کتاب Bergey، به صورت Pseudomonas  sp.  معرفی گردید. همچنین نتایج بدست آمده از اندازه‌گیری فعالیت آنزیم  ACC deaminase جدایه‌ها نشان دادکه فعالیت این آنزیم در جدایه‌های مورد آزمایش متفاوت بوده و از 43/1 تا 17/8 میکرومول آلفا- کتوبوتیرات برمیلی گرم در ساعت متغییر بود. با توجه به نتایج بدست آمده و مقایسه این داده با داده‌های سایر محققین این امیدواری وجود دارد تا تلقیح بذر کلزا با جدایه‌های فوق اثرات منفی تنش شوری را تعدیل نماید.

کلیدواژه‌ها


عنوان مقاله [English]

Isolation, Identification and Determination of ACC Deaminase Activity in Canola Rhizobacteria Isolated from Saline Soils

نویسندگان [English]

  • A. R. Akhgar 1
  • N. Saleh-Rastin 2
  • K. Khavazi 3
  • A. Shoaraye Nejati 4
1 Ph. D. Student of Soil Biology, University of Tehran
2 Associate Pofessor at University of Tehran
3 Assistant Professor, Soil and Water Research Institute
4 Expert, Soil and Water Research Institute
چکیده [English]

The proper use of saline soils to produce maximum yield of crop plants has always been a big challenge in the agricultural sector. Plants, cropped in saline soils, are affected by salinity through different ways and hence, they may not reach their maximum yield. Ethylene accumulation in the roots is one of these ways, being harmful to the plants such as canola (Brassica napus). Ethylene accumulation reduces root growth and hence crop yield. If there are ACC deaminase producing bacteria in the rhizosphere, it may be likely that these bacteria change ACC precursor to a-ketobutyrate and ammonium, resulting in the decreased ethylene level in the host plant. Hence, with respect to the importance of developing canola cropping area in Iran and the necessity to plant it in saline and relatively soils, it seemed necessary that in the first step, some bacteria, with the mentioned ability, be isolated and identified. For this reason 21 combined soil samples along with the canola roots were collected from the saline and relatively saline soils of Qom and Qazvin provinces. After determining some chemical and biological properties of the soil samples, 105 strains were selected from the soil rhizosphere of canola. According to the growing abilities of the strains in the minimum media of DF having ACC, as the only source of nitrogen, it was determined that 15 strains had the ability to produce ACC deaminase. Identifying these strains, according to the microscopy, physiological and biochemical characters, mentioned in the Bergey book, entitled, Systematic Bacteriology, showed that all the strains belonged to the group of fluorescent Pseudomonads. According to the tests, related to strain determination, 14 strains were identified as P. fluorescens. Due to the lack of accordance with the characters in the Bergey book one of the strains was identified as Pseudomonas sp. Also measuring ACC deaminase activity showed that the activity of this enzyme in the isolated strains differed from 1.43 to 8.17 mmol a-ketobutyrate/mg/hr. According to our results and in comparison with the results of other researchers, it may be beneficiary to inoculate canola seed with the identified strains to alleviate the stressful effects of salinity on canola growth and, hence yield.

کلیدواژه‌ها [English]

  • ACC deaminase
  • Pseudomonas
  • Canola
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