نوع مقاله : مقاله پژوهشی
عنوان مقاله English
نویسندگان English
1. Introduction: High temperature is a significant non-living stressor that inflicts considerable damage on the agricultural sector, particularly in vegetable production. The ability of plants to endure extreme temperatures involves complex physiological processes enabling survival under typically lethal conditions. Enhancing the intrinsic defense mechanisms of plants to cope with adverse environments is a crucial focus in the realm of biotechnology. In this context, the use of exogenous protectants, such as brassinosteroids, emerges as a promising strategy for improving plant resilience.
2. Materials and Methods: The present research was conducted in the greenhouse of Isfahan University of Technology's horticulture department on Brussels sprouts plants (var. Long Island), using a factorial design in a completely randomized layout with three replications. The aim was to investigate the effect of brassinosteroid sources on Brussels sprouts under temperature stress. The factors included two temperature regimes (25±2°C and 40±2°C) and three levels of brassinosteroid sources: distilled water (C), brassinosteroid (Br), and nano-brassinosteroid (N-Br) at a concentration of 1 µM. The seeds were planted in culture trays containing a mixture of coco peat and perlite in a 1:1 volume ratio. After the seedlings reached the 4-leaf stage, they were sprayed with 500 ml of distilled water (control), 1 µM Br, and 1 µM N-Br three times per week until the 6-leaf stage. Then, they were kept in greenhouse conditions with a temperature of 25±2°C, relative humidity of 75%, and 8 hours of darkness and 16 hours of light, respectively. Subsequently, the treatment groups were transferred to the incubator at 40±2°C under the same light, temperature, and humidity conditions as the greenhouse, except for a 6-hour heat stress at 40±2°C. At the end of the research, some characteristics of Brussels sprouts were measured.
3. Results and Discussion: The results obtained from the interaction effects of temperature regimes and brassinosteroid sources showed that shoot fresh weight, root fresh weight, and number of leaves decreased at 40°C compared to 25°C. Maximum length of the stem in both temperature regimes was observed in the control and Br treatment. Brassinosteroids, as signaling molecules, regulate both cell division and expansion. In general, the amount of proline, flavonoid, and abscisic acid increased at 40°C compared to 25°C, but no significant difference was observed between Br sources. Intracellular carbon dioxide increased at 40°C compared to 25°C, and the highest internal CO2 of stomata was observed in Br treatment compared to control and N-Br in both temperature regimes. Stomatal conductance and transpiration rate increased in both temperature regimes in the control treatment compared to Br and N-Br. When the plants had more open stomata, they had more chances for internal CO2 of stomata to enter the leaves and thus increased the rate of photosynthesis by 73% compared to the control treatment, which caused improved relative water content, internal CO2 of stomata, and the activity of antioxidant enzymes under heat stress. Brassinosteroids improve osmotic regulation, which enhances turgor pressure and regulation of stomatal conductance in plants under stress conditions. The highest amount of electrolyte leakage at 40°C was observed in the control treatment, and the lowest amount was observed in the treatment with N-Br. The activity of antioxidant enzymes increased at 40°C with Br and N-Br treatment compared to the control. Because Brassinosteroids act as secondary messengers to induce the antioxidant defense system under stress conditions, as a result, plants can effectively eliminate reactive oxygen species (ROS) in stressed plants. Moreover, by stabilizing photosynthetic pigments and preserving chloroplast ultrastructure, BRs help maintain electron transport efficiency and reduce photoinhibition under high temperature. This coordinated modulation of gas exchange, osmolyte accumulation, and redox homeostasis ultimately translates into higher biomass retention, lower membrane damage, and improved recovery capacity after heat episodes.
4. Conclusion: The Br treatment plays an important role in improving the growth of plants and increasing their resistance to high temperatures. At high temperatures, the electrolyte leakage and malondialdehyde, which are important traits of stress, increased, but Br decreased these traits by increasing the activity of antioxidant enzymes. In addition, Br was able to improve the relative water content of leaves and the rate of photosynthesis by increasing root length under temperature stress conditions. The N-Br could not significantly improve the growth and resistance of plants compared to Br.
کلیدواژهها English
