تاثیر محلول‌پاشی براسینواستروئید بر گیاهچه فلفل دلمه‌ای(Capsicum Annuum L.) تحت تنش خشکی

هورمون های گیاهی نقش موثری بر رشد و توسعه گیاهان و افزایش مقاومت به تنش ها دارند، براسینواستروئیدها از هورمون های گیاهی می باشند که به صورت موثری مقاومت به تنش خشکی را در محصولات زراعی و باغی افزایش می دهند. بنابراین در پژوهشی، تاثیر براسینواستروئید (br) بر غلظت پرولین، آمینواسید، پروتئین، محتوای آبسیزیک اسید در گیاه فلفل دلمه ای تحت تنش خشکی مورد بررسی قرار گرفت. آزمایش به صورت فاکتوریل در قالب طرح کاملاً تصادفی بر روی گیاه فلفل دلمه ای (capsicum annuum l.) رقم ̕castello چهار تیمار خشکی با استفاده از محلول پلی اتیلن گلیکول 6000 در چهار سطح صفر، 6-، -7و 8- بار اعمال شد. براسینواستروئید در دو سطح شاهد و 1 میکرومولار به حالت محلول پاشی استفاده شد. نتایج نشان داد با افزایش شدت تنش خشکی وزن تر (41 درصد) و خشک ساقه (66 درصد) کاهش یافت و شدت  اثر مخرب تنش در ساقه با کاربرد براسینواستروئید، در تنش ملایم بیشتر بود اما در ریشه در همه سطوح تنش با روند یکسانی کاهش اثرات مخرب را نشان داد. کاربرد براسینواستروئید باعث کاهش شاخص های تنش ازجمله پرولین (7 درصد) و اسیدآبسزیک (50 درصد) شد و این کاهش در میزان پرولین بخصوص در سطوح بالاتر تنش بیشتر بود. میزان اسیدآمینه و پروتئین با تنش خشکی کاهش یافت و کاربرد براسینواستروئید نتوانست به طور موثری از این کاهش خصوصاً در مورد ترکیبات و میزان آمینواسید موثر باشد. به طور کلی به نظر می رسد کاربرد براسینواستروئید در غلظت 1 میکرومولار بر موجب کاهش اثرات منفی تنش و حفظ خصوصیات رویشی گیاهچه های فلفل دلمه ای تحت تنش خشکی می گردد.

The Effect of Foliar Spray of Brassinosteroid on Sweet Pepper (Capsicum annuum L.) Seedling under Drought Stress

Introduction: Brassinosteroids promote plant growth by enhancing some metabolic activities such as photosynthesis, nucleic acid biosynthesis, proteins and carbohydrates. Mechanisms of resistance and tolerance in plants have been developed to tolerate water deficit stress. One way to deal with drought is to use plant growth regulators. Brassinosteroids were first extracted from the pollen of turnip (Brassica napus) and were considered as the sixth group of plant growth regulators. These compounds stimulate growth and cell division and affect electrical properties, membrane permeability, stability and activity of membrane enzymes. Nowadays, brassinosteroids have been extracted from various plants and their structure and function have been identified.Materials and Methods: This experiment was conducted in a factorial experiment based on a completely randomized design on Capsicum annuum L. Castello cultivar under the average daily temperature of 25 °C and 18 °C at 75% relative humidity in greenhouses. Research conducted by the College of Agriculture, Isfahan University of Technology, with four drought treatments using polyethylene glycol 6000 solutions at four levels of 0, 6, 7, and 8 bar. Brassinosteroids were sprayed in two 1 μM control levels. Pepper seeds planted in transplanting trays containing 1 to 2 volumes perlite and vermiculite substrate. When the actual leaf of seedlings appeared, the root thoroughly rinsed with distilled water and then were transferred to black plastic containers with a diameter of 16 and height 13cm and 1L volume containing Johnson’s nutrient solution including four dry treatments using 6000 polyethylene glycol solution and aerated in control for 15 minutes every 5 minutes. At the end of the experiment, vegetative factors such as fresh and dry weight of different parts of the plant, plant length, and volume, and physiological factors such as proline and abscisic acid content and chlorophyll fluorescence changes were measured.Results: The results of the analysis of variance table showed that brassinosteroid had no significant effect on most vegetative traits except root volume and weight and all physiological traits except chlorophyll fluorescence and the mentioned traits increased with the application of 1 mM brassinosteroid. However, the main effects of drought except for amino acid and the interaction of drought and brassinosteroids were significant on all traits. The results of the main drought effects showed that the root fresh weight at 8 bar and dry weight at 7 bar significantly decreased, whereas fresh and dry weight of the shoots at lower than 6 bar. The onset of decline showed that the root length and volume appeared to decrease with the onset of stress by 6 bar and the plant length also reduced with the first stress level. Drought stress at 6 bar level decreased chlorophyll fluorescence, chlorophyll index and Abscisic acid while at 7 bar decreased protein and increased proline. The results also showed that the amount of sulfuric, essential and unnecessary amino acids were significantly reduced by drought stress and brassinosteroid had no effect. Total amino acid content decreased with drought stress but there was no significant difference with control. With increasing drought stress, the fresh and dry weights of shoots decreased and the intensity of shoots decreased. The intensity of shoot growth decreased with the use of brassinosteroids at moderate stress but the mentioned trait showed the same adverse effects at all levels of stress. Brasinosteroid application decreased stress indices such as proline (7%) and abscisic acid (50%) and this decrease was more pronounced in proline, especially in more severe treatments. Amino acid and protein levels decreased with drought stress, and the use of brassinosteroids could not be effectively affected by this reduction, especially for the compounds and the amount of amino acids.The results of biplot analysis showed that the vegetative and protein traits had better mean in stress condition in the presence and absence of stress and in higher stress severity and application of brassinosteroid affected root fresh weight and abscisic acid content more than the other traits. While in mild stress it seemed to be more effectively on the steroid and most of the vegetative and physiological traits than the control.Conclusion: It seems that the application of brassinosteroids on pepper seedling in drought stress at a concentration of 1 μM is effective in maintaining vegetative properties and reducing negative effects of stress and reducing stress indices.