Rapeseed (Brassica napus L.) cultivation has been considered in Iran due to its ability to grow in different regions, high oil quality and livestock nutrition. Since Iran is located in the arid and semi-arid region of the world, the negative impacts of drought stress on rapeseed growth and production is very significant. In order to reduce the damages caused by oxidative stress, plants contain enzymatic and non-enzymatic antioxidants, including vitamin E (tocopherol). The purpose of this study was to investigate some physiological and biochemical characteristics in some rapeseed genotypes and At.TC rapeseed plants under drought stress and normal conditions. Introduction In general, having different physiological and biochemical responses in transgenic lines compared to control plants may be due to the presence of the At.TC gene, which strengthens the antioxidant defense network against stress. Conclusion The results of analysis of variance for all characteristics showed that there is a significant difference at the 1% level between genotypes, irrigation levels and Genotype- Irrigation level interaction based on Tukey test. By decreasing the field capacity and applying drought stress, it was observed that physiological traits including the content of chlorophyll b and total chlorophyll a and b were decreased. By contrast, the amount of carotenoid and proline content had an upward trend (Figure). In addition, Chlorophyll a had an ascending trend in some plants and an ascending-descending trend in some others. Moreover, biochemical characteristics such as the content of total protein, and guaiacol peroxidase and ascorbate peroxidase enzymes had an increasing trend under stress condition. Results Nima, Hyola4815, RGS003, Dalgan and Zafar genotypes besides transgenic rapeseed plants including Hyola4815 (Line5), Hyola4815 (Line6) and RGS003 (Line3) were studied at four levels of 30%, 50%, 70%, and 90% field capacity. This study is carried out through a factorial experiment based on the Completely Randomized Design with three repetitions at the University of Tehran Greenhouse. Chlorophyll content was measured based on Arnon method. The adsorption rate of the extract was read at 646, 663 and 470 nm. Then the concentrations of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids were calculated. Proline concentration was measured using the method of Betes et al.. The absorption rate at 520 nm was read by a plate reader. Bradford solution were used to evaluate total protein content and the absorbance was read by a plate reader at the wave length of 595 nm. Ascorbate peroxidase activity was measured adopting Ranieri et al. approach at 290 nm. Guaiacol peroxidase enzyme was measured by Chance and Maehly methods with a spectrophotometer at 470 nm. Data analysis was conducted using SAS 9.4 software. The average value of traits was compared using Tukey test at 5% probability level. Methods qr k h d pq mn f e r mn i b rs m i d o l g a rs m jk g s p k i pq n j c 0 5 10 15 20 90 70 50 30 Proline content (μ mol prolin/gr FW) FC (%) nima hyola RGS dalgan zafar HYOLA5 HYOLA6 RGS3 11 th International Triticale Symposium Studying the effect of drought stress on proline, chlorophyll content, protein, guaiacol peroxidase and ascorbate peroxidase in At.TC rapeseed (Brassica napus L.) Atefeh Majidi 1,* , Alireza Abbasi 2 1, 2: Agronomy and Plant Breeding Dept., University College of Agriculture and Natural Resources, University of Tehran, Iran. Figure - The rate of Proline in plants under drought stress. The studied plants included Nima, Hyola4815, RGS003, Dalgan, Zafar and transgenic lines Hyola4815 (Line5), Hyola4815 (Line6) and RGS003 (Line3). The stress levels used included 90% (control), 70%, 50%, and 30% of field capacity. Each experimental treatment had three replications. 1. Feizabadi, A., Noormohammadi, G., & Fatehi, F. (2021). Changes in growth, physiology, and fatty acid profile of rapeseed cultivars treated with vermicompost under drought stress. Journal of Soil Science and Plant Nutrition, 21(1), 200-208. 2. Zhu, J., Cai, D., Wang, J., Cao, J., Wen, Y., He, J., ... & Zhang, S. (2021). Physiological and anatomical changes in two rapeseed (Brassica napus L.) genotypes under drought stress conditions. Oil Crop Science, 6(2), 97-104. References