تاثیر پرایمینگ فیزیکی بذر و تنش کم‌آبی بر فعالیت آنزیمی و عملکرد دانه ذرت

به‌منظور بررسی تاثیر پرایمینگ فیزیکی بذر و تنش کم آبی بر فعالیت آنزیمی و عملکرد دانه ذرت، آزمایشی طی سال 1393 به‌صورت اسپلیت پلات اجرا شد. عامل اصلی شامل دو سطح آبیاری نرمال (بدون تنش) و اعمال کم‌آبی به ترتیب بر اساس 70 و 110 میلی‌متر تبخیر از تشتک تبخیر کلاس a در بعد از مرحله 9-8 برگی ذرت و عامل فرعی در یازده سطح شامل تیمار بذر ذرت با اشعه‌های گاما (کبالت 60) و بتا (استرانسیم 90) هر دو با شدت ثابت دو میکروکوری، لیزر موج پیوسته هلیم-نئون با طول‌موج 6328 آنگستروم، میدان مغناطیسی با شدت 40 میلی‌تسلا و امواج اولتراسونیک یا فراصوت با حداکثر سه وات بر سانتی‌متر مربع همگی در دو مدت‌زمان 5 و 10 دقیقه به همراه شاهد بدون تیمار بودند. اعمال تنش خشکی از مرحله 9-8 برگی به بعد غلظت پرولین برگ را 1.64 میکرومول بر گرم وزن تر افزایش داد و بیشترین غلظت این اسیدآمینه به‌ ترتیب در تیمارهای گاما 5 دقیقه‌ای، میدان‌های مغناطیسی 5 و 10 دقیقه‌ای و اولتراسونیک 5 دقیقه‌ای مشاهده گردید. در اثر اعمال تنش کم‌آبی حدود 40 درصد بر فعالیت آنزیم پراکسیداز در مقایسه با آبیاری نرمال افزوده شد و همچنین بیشترین فعالیت آن از تیمار بذر با اشعه گاما 5، میدان مغناطیسی 10، لیزر 5، بتا 5 و میدان مغناطیسی 5 دقیقه‌ای حاصل شد. وقوع تنش خشکی فعالیت آنزیم سوپر اکسید دیسموتاز را 23 درصد افزایش داد و بیشترین فعالیت این آنزیم (95.79 میکرومول بر دقیقه بر گرم) در پیش‌تیمار با اشعه لیزر 5 دقیقه‌ای مشاهده شد. بروز تنش از مرحله 98 برگی به بعد، عملکرد دانه را 18.5 درصد کاهش داد. تیمارهای میدان مغناطیسی 5 و 10 دقیقه‌ای، گاما و لیزر 5 دقیقه‌ای با میانگین 685 گرم در مترمربع دارای بیشترین عملکرد دانه بودند و افزایش زمان تیمار بذر ذرت با اشعه‌های گاما و لیزر از 5 به 10 دقیقه به ترتیب 20 و 17 درصد از عملکرد دانه کاسته شد. به نظر می رسد پیش‌تیمارهای فیزیکی بذر ذرت با میدان‌های مغناطیسی و اشعه‌های گاما و لیزر فقط در مدت‌زمان کوتاه می تواند اثرات نامطلوب تنش خشکی را کاهش دهد.

The effect of physical seed priming and water deficit stress on enzyme activity and seed yield of corn

Introduction and Objectives Seed pretreatment before sowing is a considerable solution that generally enhances the absorption of moisture, nutrients, and sunlight that therefore results in the better performance of the seeds. The negative effects of the occurrence of water deficit stress on the growth and corn yield depends on the time the stress occurs, the stage of the growth, the amount of shortage, and the environmental changes during the draught period. Among the different methods of priming, there has been a recent growing interest in using physical methods for the priming of seeds that is due to the positive effects it has on the growth of the plants. Using a number of physical factors is considered to be part of a modern method to obtain better performance in the agricultural system. The present experiment aims at investigating the effect of physical priming of seeds and water deficit stress on the enzyme activity and corn yield and also feasibility of reducing water deficit effects by using different physical priming ways. Materials and Methods The experiment was conducted as split plot based on completely randomized block design with three replications at the Agricultural Research Station of Islamic Azad University, Tabriz Branch located 15 km east of Tabriz during 2014. The main factor was consisted of two levels of normal irrigation and water deficit based on 70 (control) and 110 mm evaporation from evaporation pan respectively beginning from 89 leaves stage. The subfactor was in 11 stages including the seed treatment of the corns by different rays of gamma, beta, laser, magnetic fields and ultrasonic waves in two different durations of 5 and 10 minutes along with a controlled group, that did not receive the treatment. Before applying the physical treatment, the seeds were washed and disinfected with sodium hypochlorite after which the physical pretreatments were applied to the seeds and they were immediately sowed in the farm. The variance analysis of the data was performed by MSTATC software. The comparison of the means was done by Duncan with 5% of probability. Results The tallest plants were obtained from normal irrigation treatment whereas the shortest ones resulted from the plants with water stress. The corns exposed to the treatment of magnetic field for 5 and 10 minutes and also gamma and laser rays for 5 minutes were the highest plants. It is noteworthy that with the increase of the duration of exposure of the seeds to gamma and laser rays the height of the plants decreased. With the occurrence of water deficit stress, the activity of peroxidase enzyme increased by 40% compared to normal irrigation. The maximum activity of peroxidase enzyme was obtained after the treatments of 5minute gamma rays, 10minute magnetic field, 5minute laser rays, 10 minute beta rays and 5minute magnetic field. The occurrence of water stress enhanced the activity of superoxide dismutase compared to normal irrigation. The maximum amount of superoxide dismutase was obtained from the seed pretreatment by laser ray for 5 minutes (95.79) and 5 and 10 magnetic fields as 80.88 and 75.39 micromoles per minute per gram respectively. The effects of water deficit stress and the physical seed pretreatment were not meaningful on the number of seed rows of the maize. Due to the application of water deficit stress, an amount of approximately 170 grams per Sq.m. of the biomass of the corn reduced in comparison to normal irrigation. Following the treatments of 5minute laser ray, and 5 and 10 minute magnetic field an average amount of 16% was added to the biomass of the corns, whereas the minimum amount (945 grams per Sq.m.) was obtained with the treatment of 10minute gamma ray. The occurrence of tension after the 89 leaves stage resulted in the 18.5% decrease in the performance of the corns. The treatments of 5 and 10minute magnetic field, and 5minute gamma and laser rays had the maximum performance of the seeds with the average of 685 grams per Sq.m., while the increase of the time of seed pretreatment with gamma and laser rays from 5 to 10 minutes reduced the performance of the seeds by 20% and 17%. The seed treatment by beta ray and ultrasonic waves for both 5 and 10 minutes did not result in any considerable changes in the performance of the treated seeds compared to the controlled seeds. Conclusion The occurrence of water deficit stress after the 89 leaves stage reduced the performance of the corn seeds up to 18.5%. It seems that corn seed priming with magnetic fields and gamma and laser rays only in short terms reduces the adverse effects of drought stress and finally increases the grain yield.