تأثير پرايمينگ فيزيكي بذر و تنش كم‌آبي بر فعاليت آنزيمي و عملكرد دانه ذرت

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

به‌ منظور بررسي تأثير پرايمينگ فيزيكي بذر و تنش كم­ آبي بر فعاليت آنزيمي و عملكرد دانه ذرت، آزمايشي طي سال 1393 به‌صورت اسپليت پلات اجرا شد. عامل اصلي شامل دو سطح آبياري نرمال (بدون تنش) و اعمال كم‌آبي به ترتيب بر اساس 70 و 110 ميلي‌متر تبخير از تشتك تبخير كلاس A در بعد از مرحله 9-8 برگي ذرت و عامل فرعي در يازده سطح شامل تيمار بذر ذرت با اشعه‌هاي گاما (كبالت 60) و بتا (استرانسيم 90) هر دو با شدت ثابت دو ميكروكوري، ليزر موج پيوسته هليم- نئون با طول‌موج 6328 آنگستروم، ميدان مغناطيسي با شدت 40 ميلي‌تسلا و امواج اولتراسونيك يا فراصوت با حداكثر سه وات بر سانتي‌متر مربع همگي در دو مدت‌ زمان 5 و 10 دقيقه به همراه شاهد بدون تيمار بودند. اعمال تنش خشكي از مرحله 9-8 برگي به بعد غلظت پرولين برگ را 1.64 ميكرومول بر گرم وزن تر افزايش داد و بيشترين غلظت اين اسيدآمينه به‌ ترتيب در تيمارهاي گاما 5 دقيقه‌اي، ميدان‌هاي مغناطيسي 5 و 10 دقيقه‌اي و اولتراسونيك 5 دقيقه‌اي مشاهده گرديد. در اثر اعمال تنش كم‌آبي حدود 40 درصد بر فعاليت آنزيم پراكسيداز در مقايسه با آبياري نرمال افزوده شد و همچنين بيشترين فعاليت آن از تيمار بذر با اشعه گاما 5، ميدان مغناطيسي 10، ليزر 5، بتا 5 و ميدان مغناطيسي 5 دقيقه‌اي حاصل شد. وقوع تنش خشكي فعاليت آنزيم سوپر اكسيد ديسموتاز را 23 درصد افزايش داد و بيشترين فعاليت اين آنزيم (95.79 ميكرومول بر دقيقه بر گرم) در پيش‌تيمار با اشعه ليزر 5 دقيقه‌اي مشاهده شد. بروز تنش از مرحله 9-8 برگي به بعد، عملكرد دانه را 18.5 درصد كاهش داد. تيمارهاي ميدان مغناطيسي 5 و 10 دقيقه‌اي، گاما و ليزر 5 دقيقه‌اي با ميانگين 685 گرم در مترمربع داراي بيشترين عملكرد دانه بودند و افزايش زمان تيمار بذر ذرت با اشعه‌هاي گاما و ليزر از 5 به 10 دقيقه به ترتيب 20 و 17 درصد از عملكرد دانه كاسته شد. به نظر مي­رسد پيش‌تيمارهاي فيزيكي بذر ذرت با ميدان‌هاي مغناطيسي و اشعه‌هاي گاما و ليزر فقط در مدت‌زمان كوتاه مي ­تواند اثرات نامطلوب تنش خشكي را كاهش دهد.

Introduction and Objectives Seed pre-treatment 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 8-9 leaves stage. The sub-factor 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 pre-treatments were applied to the seeds and they were immediately sowed in the farm. The variance analysis of the data was performed by MSTAT-C 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 5-minute gamma rays, 10-minute magnetic field, 5-minute laser rays, 10- minute beta rays and 5-minute 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 pre-treatment 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 pre-treatment 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 5-minute 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 10-minute gamma ray. The occurrence of tension after the 8-9 leaves stage resulted in the 18.5% decrease in the performance of the corns. The treatments of 5 and 10-minute magnetic field, and 5-minute 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 pre-treatment 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 8-9 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.