Univrsity of Tehran Press Iranian Journal of Field Crop Science 2008-4811 56 4 2025 12 22 Pysiological and photosynthetic responses of rice (Oryza sativa L.) subsp. indica and japonica to cold stress Pysiological and photosynthetic responses of rice (Oryza sativa L.) subsp. indica and japonica to cold stress 147 162 105738 10.22059/ijfcs.2025.405517.655167 FA Eshaghi-Gorji Farid College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran 0009-0000-6706-3346 Reza Maali-Amiri College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran 0000-0003-2496-4800 Mohammadreza Ghaffari Agriculture Biotechnology Research Institute of Iran Journal Article 2025 11 04 Rice (Oryza sativa L.) as a strategic cereal makes an important contribution to ensuring food security in Iran and the world. However, its production is severely affected by abiotic stresses, including cold. This study aimed to investigate the physiological and photosynthetic responses of four cultivars of rice from the indica subspecies, including "Shiroodi" and "Hashemi" , "Kohsar" (cold-tolerant), and a japonica subspecies, including "Gerde", during cold stress of 4 °C in the growth chamber of the Faculty of Agriculture, University of Tehran in 2023 based on a factorial experiment in a completely randomized design with three replications.. Cold stress significantly increased hydrogen peroxide (H2O2) in cultivars, while its level was reduced considerably in the cultivars Gerde and Kohsar compared to Shiroodi and Hashemi, which was related to higher antioxidant capacity of the cultivars Gerde and Kohsar. The content of chlorophyll a, b, and total chlorophyll decreased significantly by 81%, 73% and 78% respectively in response to cold stress, while the decrease was less in the tolerant cultivars (Gerde and Kohsar). In contrast, carotenoids accumulation as part of the defense response significantly increased by 46%. Chlorophyll fluorescence indices showed a significant decrease up to 73%, indicating damage to photosystem II, but in the cultivars Gerde and Kohsar, decreases were less. The results indicate a direct relationship between the reduction of cellular damage, preservation of photosynthetic pigments, and stability of photosystem II in improving cold tolerance in rice, which indicates that modulating oxidative stress and cell damage increases photosynthesis and plant survival. Rice (Oryza sativa L.) as a strategic cereal makes an important contribution to ensuring food security in Iran and the world. However, its production is severely affected by abiotic stresses, including cold. This study aimed to investigate the physiological and photosynthetic responses of four cultivars of rice from the indica subspecies, including "Shiroodi" and "Hashemi" , "Kohsar" (cold-tolerant), and a japonica subspecies, including "Gerde", during cold stress of 4 °C in the growth chamber of the Faculty of Agriculture, University of Tehran in 2023 based on a factorial experiment in a completely randomized design with three replications.. Cold stress significantly increased hydrogen peroxide (H2O2) in cultivars, while its level was reduced considerably in the cultivars Gerde and Kohsar compared to Shiroodi and Hashemi, which was related to higher antioxidant capacity of the cultivars Gerde and Kohsar. The content of chlorophyll a, b, and total chlorophyll decreased significantly by 81%, 73% and 78% respectively in response to cold stress, while the decrease was less in the tolerant cultivars (Gerde and Kohsar). In contrast, carotenoids accumulation as part of the defense response significantly increased by 46%. Chlorophyll fluorescence indices showed a significant decrease up to 73%, indicating damage to photosystem II, but in the cultivars Gerde and Kohsar, decreases were less. The results indicate a direct relationship between the reduction of cellular damage, preservation of photosynthetic pigments, and stability of photosystem II in improving cold tolerance in rice, which indicates that modulating oxidative stress and cell damage increases photosynthesis and plant survival. https://ijfcs.ut.ac.ir/article_105738_8c807d2ae934fc502b1c892bcc822125.pdf