Biochemical and Physiological Responses of Alfalfa (Medicago sativa L.) Cultivars to Osmotic Stress

Document Type : Research Paper


1 Department of Biology, Tonekabon Branch, Islamic Azad University, Tonekabon, Iran

2 Department of Biology, College of Sciences, Yadegar-e- Imam Khomeini (RAH) Shahre Rey Branch, Islamic Azad University, Tehran, Iran

3 Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran


In order to investigate the effects of water stress on total phenolics content, antioxidant power, β-glucosidase activity and stomatal properties of alfalfa, a factorial experiment based on randomized complete block design was carried out in 1-Lit pots containing half strength Hoagland culture medium using two cultivars of alfalfa at four osmotic pressures including 0 (control), -0.5, -1.0 and -1.5 MPa. Polyphenol oxidase activity and total phenolics were increased in both cultivars in response to osmotic stress. Although the increases in total phenolics were higher in Yazdi cultivar than Gharayonjeh but the polyphenol oxidase activity had an inverse trend, thus resulting in higher levels of phenolic compounds in Yazdi cultivar than Gharayonjeh. The β-glucosidase activity as a marker of ABA level in plant cells increased in both cultivars. Furthermore, stomatal conductance and transpiration rates decreased in response to drought stress. This means that both cultivars closed their stomata under osmotic pressure in order to reduce the transpiration, however, Yazdi cultivar was more efficient in this respect. According to our results, it can be concluded that Yazdi can be considered as a more tolerant cultivar than Gharayonjeh because of its ability to increase free ABA levels in leaves, reduce transpiration rate and accumulate antioxidant compounds.


Article Title [فارسی]

پاسخ‌های بیوشیمیایی و فیزیولوژیک ارقام گیاه یونجه به تنش اسمزی

Abstract [فارسی]

به منظور بررسی تاثیر تنش آبی روی محتوای فنل کل، قدرت آنتی‌اکسیدانی، فعالیت β-گلوکوزیداز و ویژگی‌های روزنه­ای گیاه یونجه، یک آزمایش فاکتوریل به صورت کاملا تصادفی با استفاده از دو واریته یونجه در چهار فشار اسمزی شامل 0، 0.5-، 1- و 1/5- مگاپاسکال انجام شد. بر اساس نتایج به دست آمده فعالیت PPO و فنل کل در هر دو واریته در پاسخ به تنش آبی افزایش یافت اگرچه افزایش در فنل کل در واریته یزدی بیشتر از واریته قره‌ یونجه بود، ولی فعالیت PPO عملکردی معکوس نشان داد. فعالیت β-گلوکوزیداز به عنوان شاخص سطح ABA در سلول‌های گیاهی در هر دو واریته افزایش و هدایت روزنه‌ای و مقدار تنفس در پاسخ به تنش خشکی کاهش یافت. لذا هر دو واریته به منظور کاهش تنفس تمایل به بستن روزنه داشتند ولی واریته یزدی توانایی بهتری برای انجام این کار نشان داد. بنابراین، واریته یزدی را به دلیل افزایش در مقدار ABA آزاد در برگ‌ها، کاهش مقدار تنفس و تجمع ترکیبات آنتی‌اکسیدان می‌توان واریته‌ای با تحمل بیشتر نسبت به واریته قره یونجه در نظر گرفت.

Keywords [فارسی]

  • ترکیبات فنلی
  • تنش اسمزی
  • یونجه
  • β-گلوکوزیداز
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