Investigating the Physiological Responses of Rye (Secale cereale L.) to Aluminum Chloride and Freeze-Thaw Stress with Citric Acid as a Resilience Enhancer

Freeze-thaw cycles and aluminum chloride are significant environmental stressors, particularly in northern regions. The study explores how exogenous citric acid (CA), can mitigate the negative effects of freeze-thaw (FT) and aluminum (Al) stress. Conducted in tray pots with nutrient solution under controlled lab conditions, the experiment examines the impact of CA (150 mu M) on growth, antioxidant systems, osmolyte accumulation, and photosynthetic activity under Al stress (200 mu M). Results show that Al stress inhibits growth, induces reactive oxygen species (ROS), and causes membrane peroxidation, activating antioxidant defenses. CA treatment counteracts Al-induced growth inhibition by reducing ROS and boosting antioxidant activity. Under Al and combined Al + FT stress, levels of malondialdehyde (MDA), soluble protein (SP), superoxide dismutase (SOD), and peroxidase (POD) increased, while net photosynthetic rate (Pn) and transpiration rate (Tr) declined. CA reversed these effects, raising Pn and Tr and lowering MDA levels. This indicates that CA enhances rye seedling tolerance by strengthening osmotic regulation and antioxidant enzymes, aiding resilience under Al and FT stress.