دانشگاه اصفهان علوم زیستی گیاهی 3041-9603 17 1 2025 05 22 Effect of salicylic acid on the antioxidant enzyme system and hydrogen peroxide production in safflower under heat stress اثر محلول ‌پاشی سالیسیلیک اسید بر سیستم آنزیم ‌‌های آنتی‌اکسیدان و تولید پراکسیدهیدروژن گیاه گلرنگ در شرایط تنش گرما 95 118 29958 10.22108/ijpb.2025.144801.1404 FA مریم گودرزیان قهفرخی گروه مهندسی تولید و ژنتیک گیاهی، دانشکدۀ کشاورزی، دانشگاه شهید چمران اهواز، اهواز، ایران افراسیاب راهنما گروه مهندسی تولید و ژنتیک گیاهی، دانشکدۀ کشاورزی، دانشگاه شهید چمران اهواز، اهواز، ایران موسی مسکرباشی گروه مهندسی تولید و ژنتیک گیاهی، دانشکدۀ کشاورزی، دانشگاه شهید چمران اهواز، اهواز، ایران فرشاد صالحی مؤسسۀ تحقیقات و آموزش توسعۀ نیشکر و صنایع جانبی خوزستان، اهواز، ایران دونالد اسمیت گروه علوم گیاهی، دانشکدۀ علوم محیطی و کشاورزی، دانشگاه مک گیل، مونترال، کانادا Journal Article 2025 03 30 To study the effects of foliar application of salicylic acid on antioxidant enzyme activities and hydrogen peroxide production in safflower, a field experiment was conducted in a split-plot factorial randomized complete block design with three replications in 2019. Main plots consisted of two sowing dates: 11 December and 21 January, and subplots consisted of a factorial arrangement of different concentrations of salicylic acid (0 and 400 μm), and safflower cultivars (Parnian and Faraman). The results showed that heat stress at late sowing dates significantly increased hydrogen peroxide concentration, with higher values observed in the Parnian than the Faraman cultivar. Total antioxidant capacity in Parnian and Faraman increased following foliar application of salicylic acid, especially at 400 μm (36.7% and 46.5%, respectively). The highest catalase, ascorbate-peroxidase, and superoxide dismutase activity (346.5, 45.9, and 141.5 mg protein.min^-1, respectively) was observed in Faraman at a 400 μm salicylic acid level. In addition, heat stress increased polyphenol oxidase activity in both foliar application treatments, and Faraman showed higher activity than Parnian. The highest lipoxygenase activity was observed under heat stress, without salicylic acid application, in Parnian (65.7 mg protein.min^-1). The highest phenylalanine ammonia-lyase activity was observed in Faraman under heat stress and at a 400 μm salicylic acid level (116.5 mg of protein.min^-1). Exogenous application of salicylic acid could modulate the adverse effects of heat stress by improving biochemical properties and resulted in heat tolerance in both cultivars when compared with the control.<br /><strong> </strong><br /><strong>Introduction </strong><br />Safflower is an oilseed crop mainly cultivated for purposes relating to household and industrial consumption. Global warming and climate change pose serious threats to agriculture and food security. Extreme weather events resulting from climate change have reduced crop production and productivity worldwide. High temperatures are affecting crop productivity, potentially compromising food security. Plants possess various defence mechanisms to cope with environmental challenges, and high temperatures pose a significant threat due to global warming. Delays in sowing date are known to accelerate crop development and shorten the growing season, increasing the distance the plant is from suitable growing conditions and exposing it to high temperatures during reproductive growth. Salicylic acid is critical for controlling plant growth and development, interactions with other plant hormones, and responses to environmental stress. Salicylic acid plays a role in plant defence systems against various biotic and abiotic stresses and may also help plants cope with high temperatures. Exogenous salicylic acid application alters hydrogen peroxide production and increases antioxidant system activity under high temperatures. Hence, the current study aimed to evaluate the effect of foliar salicylic acid application on antioxidant enzyme activities and hydrogen peroxide production in safflower under terminal heat stress.<br /> <br /><strong>Materials and Methods</strong><br />To evaluate the foliar application of salicylic acid on the antioxidant enzyme system and hydrogen peroxide production in safflower, a field experiment was carried out in a split-plot factorial randomized complete block design with three replications at Shahid Chamran University of Ahvaz in 2019, main plots consisted of two sowing dates: 11th December and 21st January (Normal and late sowing dates, respectively), and the plot consisted of a factorial arrangement of different concentrations of salicylic acid (0 and 400 μm), and safflower cultivars (Parnian as a heat-sensitive and Faraman as a heat-tolerant cultivar). The soil texture in the topsoil at the study site was sandy-loam. Electrical conductivity of the topsoil was 4.8 dS.m^-1, and pH was 7.6. On 21 January, as a late sowing date, the flowering and grain-filling periods were exposed to severe heat stress at the end of the growing season. Hormonal treatments were applied at the rosette and beginning of flowering elongation (stage 30-31 and 60-61 of the BBCH scale, respectively). Plants were watered with sufficient water (80% field capacity) until the end of the experiment. Weeds were removed by hand every two weeks during the growing season. Data on hydrogen peroxide concentration, catalase activity, ascorbate peroxidase, superoxide dismutase, glutathione reductase, guaiacol peroxidase, polyphenol oxidase, lipoxygenases, phenylalanine ammonia lyase, and DPPH were recorded.<br /> <br /><strong>Results and Discussion</strong><br />The results showed that terminal heat stress caused by late sowing dates significantly increased hydrogen peroxide concentration. The higher values observed in the Parnian cultivar (0.0200 μm.gfw^-1) than in the Faraman cultivar (0.0095 μm.gfw^-1). Total antioxidant capacity in Parnian and Faraman increased following foliar application of salicylic acid, especially at 400 μm (36.7% and 46.5%, respectively), compared with the control. The highest catalase, ascorbate-peroxidase, and superoxide dismutase activity (346.5, 45.9, and 141.5 mg protein.min^-1, respectively) was observed in Faraman at a 400 μm salicylic acid level. In addition, heat stress increased polyphenol oxidase activity in both foliar application treatments (69.2% and 24.2%, respectively) compared with the control, and Faraman showed higher enzyme activity than Parnian. The highest lipoxygenase activity was observed under heat stress, without salicylic acid application, in Parnian (65.7 mg protein.min^-1). The highest phenylalanine ammonia-lyase activity was observed in Faraman under heat stress and at a 400 μm salicylic acid level (116.5 mg of protein.min^-1).<br /> <br /><strong>Conclusion</strong><br />In this study, safflower cultivars showed changes in antioxidant enzyme activities and hydrogen peroxide production under high-temperature conditions. Hence, we focused on the foliar application of salicylic acid and its effects on the antioxidant activity of safflower cultivars under heat stress to highlight the role of salicylic acid in heat stress response and its potential to increase heat stress tolerance in safflower. We found that safflower cultivars vary widely in hydrogen peroxide production and antioxidant enzyme activities. The results of this experiment showed that heat stress increased hydrogen peroxide accumulation. To overcome these conditions, exogenous application of salicylic acid could modulate the adverse effects of heat stress by improving antioxidant capacity and resulting in high-temperature tolerance in both safflower cultivars in tropical regions such as Khuzestan. جهت بررسی اثر محلول پاشی سالیسیلیک اسید بر فعالیت آنزیم­های آنتی اکسیدانی و تولید پراکسید هیدروژن در گلرنگ در شرایط تنش گرما آزمایش مزرعه­ای در سال زراعی 98-1397 به­صورت اسپلیت فاکتوریل در قالب طرح پایۀ بلوک­های کامل تصادفی در سه تکرار انجام شد. دو تاریخ کاشت 20 آذر و 30 دی در کرت­های اصلی و محلول­پاشی سالسیلیک اسید (صفر و 400 میکرومولار) و دو رقم گلرنگ (پرنیان و فرامان) به­صورت فاکتوریل در کرت­های فرعی قرار گرفتند. تنش گرما سبب افزایش غلظت پراکسیدهیدروژن شد و مقدار آن در رقم پرنیان بالاتر از فرامان بود. همچنین دمای بالا سبب افزایش ظرفیت آنتی­اکسیدانی کل در رقم پرنیان و فرامان به ویژه در شرایط 400 میکرومولار سالیسیلیک اسید (به ترتیب 7‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏/36 و 5‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏/46 درصد) شد. بیشترین فعالیت کاتالاز، آسکوربات­پراکسیداز و سوپراکسیددیسموتاز (به ترتیب 5‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏/346، 9‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏/45 و 5‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏/141 میلی­ گرم پروتئین بر دقیقه) در شرایط کاربرد 400 میکرو­مولار سالسیلیک اسید در رقم فرامان مشاهده شد. تنش گرما موجب افزایش فعالیت پلی‌فنول‌اکسیداز شد و رقم فرامان فعالیت بالاتری داشت. بالاترین فعالیت لیپوکسی­ژناز در شرایط گرما تحت تیمار شاهد در رقم پرنیان (7‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏/65 تغییرات جذب بر میلی­گرم پروتئین بر دقیقه) و بیشترین فعالیت فنیل‌آلانین‌آمونیالیاز مربوط به رقم فرامان در شرایط تنش گرما و محلول‌پاشی 400 میکرو­مولار سالسیلیک اسید (5‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏/116 میلی­گرم پروتئین بر دقیقه) مشاهده شد. در مجموع، یافته‌ها نشان داد اسیدسالیسیلیک توانست اثرات نامطلوب تنش گرما را توسط بهبود صفات بیوشیمیایی تعدیل بخشد و منجر به تحمل گرما در هر دو رقم به ویژه در رقم متحمل به گرمای فرامان در مقایسه با شرایط شاهد شود. https://ijpb.ui.ac.ir/article_29958_383f5e079335d95bb787c7251ad08f26.pdf